[rust.git] / src / librustc / back / link.rs

// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.


use back::archive::{Archive, METADATA_FILENAME};
use back::rpath;
use back::manifest;
use driver::driver::CrateTranslation;
use driver::session::Session;
use driver::session;
use lib::llvm::llvm;
use lib::llvm::ModuleRef;
use lib;
use metadata::common::LinkMeta;
use metadata::{encoder, cstore, filesearch, csearch};
use middle::trans::context::CrateContext;
use middle::trans::common::gensym_name;
use middle::ty;
use util::common::time;
use util::ppaux;
use util::sha2::{Digest, Sha256};

use std::c_str::ToCStr;
use std::char;
use std::os::consts::{macos, freebsd, linux, android, win32};
use std::ptr;
use std::run;
use std::str;
use std::io;
use std::io::fs;
use extra::tempfile::TempDir;
use syntax::abi;
use syntax::ast;
use syntax::ast_map::{path, path_mod, path_name, path_pretty_name};
use syntax::attr;
use syntax::attr::AttrMetaMethods;
use syntax::pkgid::PkgId;

#[deriving(Clone, Eq)]
pub enum output_type {
    output_type_none,
    output_type_bitcode,
    output_type_assembly,
    output_type_llvm_assembly,
    output_type_object,
    output_type_exe,
}

pub fn llvm_err(sess: Session, msg: ~str) -> ! {
    unsafe {
        let cstr = llvm::LLVMRustGetLastError();
        if cstr == ptr::null() {
            sess.fatal(msg);
        } else {
            sess.fatal(msg + ": " + str::raw::from_c_str(cstr));
        }
    }
}

pub fn WriteOutputFile(
        sess: Session,
        Target: lib::llvm::TargetMachineRef,
        PM: lib::llvm::PassManagerRef,
        M: ModuleRef,
        Output: &Path,
        FileType: lib::llvm::FileType) {
    unsafe {
        Output.with_c_str(|Output| {
            let result = llvm::LLVMRustWriteOutputFile(
                    Target, PM, M, Output, FileType);
            if !result {
                llvm_err(sess, ~"Could not write output");
            }
        })
    }
}

pub mod write {

    use back::lto;
    use back::link::{WriteOutputFile, output_type};
    use back::link::{output_type_assembly, output_type_bitcode};
    use back::link::{output_type_exe, output_type_llvm_assembly};
    use back::link::{output_type_object};
    use driver::driver::CrateTranslation;
    use driver::session::Session;
    use driver::session;
    use lib::llvm::llvm;
    use lib::llvm::{ModuleRef, TargetMachineRef, PassManagerRef};
    use lib;
    use util::common::time;

    use std::c_str::ToCStr;
    use std::io;
    use std::libc::{c_uint, c_int};
    use std::path::Path;
    use std::run;
    use std::str;

    pub fn run_passes(sess: Session,
                      trans: &CrateTranslation,
                      output_type: output_type,
                      output: &Path) {
        let llmod = trans.module;
        let llcx = trans.context;
        unsafe {
            llvm::LLVMInitializePasses();

            // Only initialize the platforms supported by Rust here, because
            // using --llvm-root will have multiple platforms that rustllvm
            // doesn't actually link to and it's pointless to put target info
            // into the registry that Rust can not generate machine code for.
            llvm::LLVMInitializeX86TargetInfo();
            llvm::LLVMInitializeX86Target();
            llvm::LLVMInitializeX86TargetMC();
            llvm::LLVMInitializeX86AsmPrinter();
            llvm::LLVMInitializeX86AsmParser();

            llvm::LLVMInitializeARMTargetInfo();
            llvm::LLVMInitializeARMTarget();
            llvm::LLVMInitializeARMTargetMC();
            llvm::LLVMInitializeARMAsmPrinter();
            llvm::LLVMInitializeARMAsmParser();

            llvm::LLVMInitializeMipsTargetInfo();
            llvm::LLVMInitializeMipsTarget();
            llvm::LLVMInitializeMipsTargetMC();
            llvm::LLVMInitializeMipsAsmPrinter();
            llvm::LLVMInitializeMipsAsmParser();

            if sess.opts.save_temps {
                output.with_extension("no-opt.bc").with_c_str(|buf| {
                    llvm::LLVMWriteBitcodeToFile(llmod, buf);
                })
            }

            configure_llvm(sess);

            let OptLevel = match sess.opts.optimize {
              session::No => lib::llvm::CodeGenLevelNone,
              session::Less => lib::llvm::CodeGenLevelLess,
              session::Default => lib::llvm::CodeGenLevelDefault,
              session::Aggressive => lib::llvm::CodeGenLevelAggressive,
            };
            let use_softfp = sess.opts.debugging_opts & session::use_softfp != 0;

            let tm = sess.targ_cfg.target_strs.target_triple.with_c_str(|T| {
                sess.opts.target_cpu.with_c_str(|CPU| {
                    sess.opts.target_feature.with_c_str(|Features| {
                        llvm::LLVMRustCreateTargetMachine(
                            T, CPU, Features,
                            lib::llvm::CodeModelDefault,
                            lib::llvm::RelocPIC,
                            OptLevel,
                            true,
                            use_softfp
                        )
                    })
                })
            });

            // Create the two optimizing pass managers. These mirror what clang
            // does, and are by populated by LLVM's default PassManagerBuilder.
            // Each manager has a different set of passes, but they also share
            // some common passes.
            let fpm = llvm::LLVMCreateFunctionPassManagerForModule(llmod);
            let mpm = llvm::LLVMCreatePassManager();

            // If we're verifying or linting, add them to the function pass
            // manager.
            let addpass = |pass: &str| {
                pass.with_c_str(|s| llvm::LLVMRustAddPass(fpm, s))
            };
            if !sess.no_verify() { assert!(addpass("verify")); }
            if sess.lint_llvm()  { assert!(addpass("lint"));   }

            if !sess.no_prepopulate_passes() {
                llvm::LLVMRustAddAnalysisPasses(tm, fpm, llmod);
                llvm::LLVMRustAddAnalysisPasses(tm, mpm, llmod);
                populate_llvm_passes(fpm, mpm, llmod, OptLevel);
            }

            for pass in sess.opts.custom_passes.iter() {
                pass.with_c_str(|s| {
                    if !llvm::LLVMRustAddPass(mpm, s) {
                        sess.warn(format!("Unknown pass {}, ignoring", *pass));
                    }
                })
            }

            // Finally, run the actual optimization passes
            time(sess.time_passes(), "llvm function passes", (), |()|
                 llvm::LLVMRustRunFunctionPassManager(fpm, llmod));
            time(sess.time_passes(), "llvm module passes", (), |()|
                 llvm::LLVMRunPassManager(mpm, llmod));

            // Deallocate managers that we're now done with
            llvm::LLVMDisposePassManager(fpm);
            llvm::LLVMDisposePassManager(mpm);

            // Emit the bytecode if we're either saving our temporaries or
            // emitting an rlib. Whenever an rlib is create, the bytecode is
            // inserted into the archive in order to allow LTO against it.
            if sess.opts.save_temps ||
               sess.outputs.iter().any(|&o| o == session::OutputRlib) {
                output.with_extension("bc").with_c_str(|buf| {
                    llvm::LLVMWriteBitcodeToFile(llmod, buf);
                })
            }

            if sess.lto() {
                time(sess.time_passes(), "all lto passes", (), |()|
                     lto::run(sess, llmod, tm, trans.reachable));

                if sess.opts.save_temps {
                    output.with_extension("lto.bc").with_c_str(|buf| {
                        llvm::LLVMWriteBitcodeToFile(llmod, buf);
                    })
                }
            }

            // A codegen-specific pass manager is used to generate object
            // files for an LLVM module.
            //
            // Apparently each of these pass managers is a one-shot kind of
            // thing, so we create a new one for each type of output. The
            // pass manager passed to the closure should be ensured to not
            // escape the closure itself, and the manager should only be
            // used once.
            fn with_codegen(tm: TargetMachineRef, llmod: ModuleRef,
                            f: |PassManagerRef|) {
                unsafe {
                    let cpm = llvm::LLVMCreatePassManager();
                    llvm::LLVMRustAddAnalysisPasses(tm, cpm, llmod);
                    llvm::LLVMRustAddLibraryInfo(cpm, llmod);
                    f(cpm);
                    llvm::LLVMDisposePassManager(cpm);
                }
            }

            time(sess.time_passes(), "codegen passes", (), |()| {
                match output_type {
                    output_type_none => {}
                    output_type_bitcode => {
                        output.with_c_str(|buf| {
                            llvm::LLVMWriteBitcodeToFile(llmod, buf);
                        })
                    }
                    output_type_llvm_assembly => {
                        output.with_c_str(|output| {
                            with_codegen(tm, llmod, |cpm| {
                                llvm::LLVMRustPrintModule(cpm, llmod, output);
                            })
                        })
                    }
                    output_type_assembly => {
                        with_codegen(tm, llmod, |cpm| {
                            WriteOutputFile(sess, tm, cpm, llmod, output,
                                            lib::llvm::AssemblyFile);
                        });

                        // If we're not using the LLVM assembler, this function
                        // could be invoked specially with output_type_assembly,
                        // so in this case we still want the metadata object
                        // file.
                        if sess.opts.output_type != output_type_assembly {
                            with_codegen(tm, trans.metadata_module, |cpm| {
                                let out = output.with_extension("metadata.o");
                                WriteOutputFile(sess, tm, cpm,
                                                trans.metadata_module, &out,
                                                lib::llvm::ObjectFile);
                            })
                        }
                    }
                    output_type_exe | output_type_object => {
                        with_codegen(tm, llmod, |cpm| {
                            WriteOutputFile(sess, tm, cpm, llmod, output,
                                            lib::llvm::ObjectFile);
                        });
                        with_codegen(tm, trans.metadata_module, |cpm| {
                            let out = output.with_extension("metadata.o");
                            WriteOutputFile(sess, tm, cpm,
                                            trans.metadata_module, &out,
                                            lib::llvm::ObjectFile);
                        })
                    }
                }
            });

            llvm::LLVMRustDisposeTargetMachine(tm);
            llvm::LLVMDisposeModule(trans.metadata_module);
            llvm::LLVMDisposeModule(llmod);
            llvm::LLVMContextDispose(llcx);
            if sess.time_llvm_passes() { llvm::LLVMRustPrintPassTimings(); }
        }
    }

    pub fn run_assembler(sess: Session, assembly: &Path, object: &Path) {
        let cc = super::get_cc_prog(sess);

        // FIXME (#9639): This needs to handle non-utf8 paths
        let args = [
            ~"-c",
            ~"-o", object.as_str().unwrap().to_owned(),
            assembly.as_str().unwrap().to_owned()];

        debug!("{} '{}'", cc, args.connect("' '"));
        let opt_prog = {
            let _guard = io::ignore_io_error();
            run::process_output(cc, args)
        };
        match opt_prog {
            Some(prog) => {
                if !prog.status.success() {
                    sess.err(format!("linking with `{}` failed: {}", cc, prog.status));
                    sess.note(format!("{} arguments: '{}'", cc, args.connect("' '")));
                    sess.note(str::from_utf8_owned(prog.error + prog.output));
                    sess.abort_if_errors();
                }
            },
            None => {
                sess.err(format!("could not exec the linker `{}`", cc));
                sess.abort_if_errors();
            }
        }
    }

    unsafe fn configure_llvm(sess: Session) {
        // Copy what clan does by turning on loop vectorization at O2 and
        // slp vectorization at O3
        let vectorize_loop = !sess.no_vectorize_loops() &&
                             (sess.opts.optimize == session::Default ||
                              sess.opts.optimize == session::Aggressive);
        let vectorize_slp = !sess.no_vectorize_slp() &&
                            sess.opts.optimize == session::Aggressive;

        let mut llvm_c_strs = ~[];
        let mut llvm_args = ~[];
        let add = |arg: &str| {
            let s = arg.to_c_str();
            llvm_args.push(s.with_ref(|p| p));
            llvm_c_strs.push(s);
        };
        add("rustc"); // fake program name
        add("-arm-enable-ehabi");
        add("-arm-enable-ehabi-descriptors");
        if vectorize_loop { add("-vectorize-loops"); }
        if vectorize_slp  { add("-vectorize-slp");   }
        if sess.time_llvm_passes() { add("-time-passes"); }
        if sess.print_llvm_passes() { add("-debug-pass=Structure"); }

        for arg in sess.opts.llvm_args.iter() {
            add(*arg);
        }

        llvm::LLVMRustSetLLVMOptions(llvm_args.len() as c_int, llvm_args.as_ptr());
    }

    unsafe fn populate_llvm_passes(fpm: lib::llvm::PassManagerRef,
                                   mpm: lib::llvm::PassManagerRef,
                                   llmod: ModuleRef,
                                   opt: lib::llvm::CodeGenOptLevel) {
        // Create the PassManagerBuilder for LLVM. We configure it with
        // reasonable defaults and prepare it to actually populate the pass
        // manager.
        let builder = llvm::LLVMPassManagerBuilderCreate();
        match opt {
            lib::llvm::CodeGenLevelNone => {
                // Don't add lifetime intrinsics add O0
                llvm::LLVMRustAddAlwaysInlinePass(builder, false);
            }
            lib::llvm::CodeGenLevelLess => {
                llvm::LLVMRustAddAlwaysInlinePass(builder, true);
            }
            // numeric values copied from clang
            lib::llvm::CodeGenLevelDefault => {
                llvm::LLVMPassManagerBuilderUseInlinerWithThreshold(builder,
                                                                    225);
            }
            lib::llvm::CodeGenLevelAggressive => {
                llvm::LLVMPassManagerBuilderUseInlinerWithThreshold(builder,
                                                                    275);
            }
        }
        llvm::LLVMPassManagerBuilderSetOptLevel(builder, opt as c_uint);
        llvm::LLVMRustAddBuilderLibraryInfo(builder, llmod);

        // Use the builder to populate the function/module pass managers.
        llvm::LLVMPassManagerBuilderPopulateFunctionPassManager(builder, fpm);
        llvm::LLVMPassManagerBuilderPopulateModulePassManager(builder, mpm);
        llvm::LLVMPassManagerBuilderDispose(builder);
    }
}


/*
 * Name mangling and its relationship to metadata. This is complex. Read
 * carefully.
 *
 * The semantic model of Rust linkage is, broadly, that "there's no global
 * namespace" between crates. Our aim is to preserve the illusion of this
 * model despite the fact that it's not *quite* possible to implement on
 * modern linkers. We initially didn't use system linkers at all, but have
 * been convinced of their utility.
 *
 * There are a few issues to handle:
 *
 *  - Linkers operate on a flat namespace, so we have to flatten names.
 *    We do this using the C++ namespace-mangling technique. Foo::bar
 *    symbols and such.
 *
 *  - Symbols with the same name but different types need to get different
 *    linkage-names. We do this by hashing a string-encoding of the type into
 *    a fixed-size (currently 16-byte hex) cryptographic hash function (CHF:
 *    we use SHA256) to "prevent collisions". This is not airtight but 16 hex
 *    digits on uniform probability means you're going to need 2**32 same-name
 *    symbols in the same process before you're even hitting birthday-paradox
 *    collision probability.
 *
 *  - Symbols in different crates but with same names "within" the crate need
 *    to get different linkage-names.
 *
 *  - The hash shown in the filename needs to be predictable and stable for
 *    build tooling integration. It also needs to be using a hash function
 *    which is easy to use from Python, make, etc.
 *
 * So here is what we do:
 *
 *  - Consider the package id; every crate has one (specified with pkgid
 *    attribute).  If a package id isn't provided explicitly, we infer a
 *    versionless one from the output name. The version will end up being 0.0
 *    in this case. CNAME and CVERS are taken from this package id. For
 *    example, github.com/mozilla/CNAME#CVERS.
 *
 *  - Define CMH as SHA256(pkgid).
 *
 *  - Define CMH8 as the first 8 characters of CMH.
 *
 *  - Compile our crate to lib CNAME-CMH8-CVERS.so
 *
 *  - Define STH(sym) as SHA256(CMH, type_str(sym))
 *
 *  - Suffix a mangled sym with ::STH@CVERS, so that it is unique in the
 *    name, non-name metadata, and type sense, and versioned in the way
 *    system linkers understand.
 */

pub fn build_link_meta(sess: Session,
                       attrs: &[ast::Attribute],
                       output: &Path,
                       symbol_hasher: &mut Sha256)
                       -> LinkMeta {
    // This calculates CMH as defined above
    fn crate_hash(symbol_hasher: &mut Sha256, pkgid: &PkgId) -> @str {
        symbol_hasher.reset();
        symbol_hasher.input_str(pkgid.to_str());
        truncated_hash_result(symbol_hasher).to_managed()
    }

    let pkgid = match attr::find_pkgid(attrs) {
        None => {
            let stem = session::expect(
                sess,
                output.filestem_str(),
                || format!("output file name '{}' doesn't appear to have a stem",
                           output.display()));
            from_str(stem).unwrap()
        }
        Some(s) => s,
    };

    let hash = crate_hash(symbol_hasher, &pkgid);

    LinkMeta {
        pkgid: pkgid,
        crate_hash: hash,
    }
}

pub fn truncated_hash_result(symbol_hasher: &mut Sha256) -> ~str {
    symbol_hasher.result_str()
}


// This calculates STH for a symbol, as defined above
pub fn symbol_hash(tcx: ty::ctxt,
                   symbol_hasher: &mut Sha256,
                   t: ty::t,
                   link_meta: &LinkMeta) -> @str {
    // NB: do *not* use abbrevs here as we want the symbol names
    // to be independent of one another in the crate.

    symbol_hasher.reset();
    symbol_hasher.input_str(link_meta.pkgid.name);
    symbol_hasher.input_str("-");
    symbol_hasher.input_str(link_meta.crate_hash);
    symbol_hasher.input_str("-");
    symbol_hasher.input_str(encoder::encoded_ty(tcx, t));
    let mut hash = truncated_hash_result(symbol_hasher);
    // Prefix with 'h' so that it never blends into adjacent digits
    hash.unshift_char('h');
    // tjc: allocation is unfortunate; need to change std::hash
    hash.to_managed()
}

pub fn get_symbol_hash(ccx: &mut CrateContext, t: ty::t) -> @str {
    match ccx.type_hashcodes.find(&t) {
      Some(&h) => h,
      None => {
        let hash = symbol_hash(ccx.tcx, &mut ccx.symbol_hasher, t, &ccx.link_meta);
        ccx.type_hashcodes.insert(t, hash);
        hash
      }
    }
}


// Name sanitation. LLVM will happily accept identifiers with weird names, but
// gas doesn't!
// gas accepts the following characters in symbols: a-z, A-Z, 0-9, ., _, $
pub fn sanitize(s: &str) -> ~str {
    let mut result = ~"";
    for c in s.chars() {
        match c {
            // Escape these with $ sequences
            '@' => result.push_str("$SP$"),
            '~' => result.push_str("$UP$"),
            '*' => result.push_str("$RP$"),
            '&' => result.push_str("$BP$"),
            '<' => result.push_str("$LT$"),
            '>' => result.push_str("$GT$"),
            '(' => result.push_str("$LP$"),
            ')' => result.push_str("$RP$"),
            ',' => result.push_str("$C$"),

            // '.' doesn't occur in types and functions, so reuse it
            // for ':' and '-'
            '-' | ':' => result.push_char('.'),

            // These are legal symbols
            'a' .. 'z'
            | 'A' .. 'Z'
            | '0' .. '9'
            | '_' | '.' | '$' => result.push_char(c),

            _ => {
                let mut tstr = ~"";
                char::escape_unicode(c, |c| tstr.push_char(c));
                result.push_char('$');
                result.push_str(tstr.slice_from(1));
            }
        }
    }

    // Underscore-qualify anything that didn't start as an ident.
    if result.len() > 0u &&
        result[0] != '_' as u8 &&
        ! char::is_XID_start(result[0] as char) {
        return ~"_" + result;
    }

    return result;
}

pub fn mangle(sess: Session, ss: path,
              hash: Option<&str>, vers: Option<&str>) -> ~str {
    // Follow C++ namespace-mangling style, see
    // http://en.wikipedia.org/wiki/Name_mangling for more info.
    //
    // It turns out that on OSX you can actually have arbitrary symbols in
    // function names (at least when given to LLVM), but this is not possible
    // when using unix's linker. Perhaps one day when we just a linker from LLVM
    // we won't need to do this name mangling. The problem with name mangling is
    // that it seriously limits the available characters. For example we can't
    // have things like @T or ~[T] in symbol names when one would theoretically
    // want them for things like impls of traits on that type.
    //
    // To be able to work on all platforms and get *some* reasonable output, we
    // use C++ name-mangling.

    let mut n = ~"_ZN"; // _Z == Begin name-sequence, N == nested

    let push = |s: &str| {
        let sani = sanitize(s);
        n.push_str(format!("{}{}", sani.len(), sani));
    };

    // First, connect each component with <len, name> pairs.
    for s in ss.iter() {
        match *s {
            path_name(s) | path_mod(s) | path_pretty_name(s, _) => {
                push(sess.str_of(s))
            }
        }
    }

    // next, if any identifiers are "pretty" and need extra information tacked
    // on, then use the hash to generate two unique characters. For now
    // hopefully 2 characters is enough to avoid collisions.
    static EXTRA_CHARS: &'static str =
        "abcdefghijklmnopqrstuvwxyz\
         ABCDEFGHIJKLMNOPQRSTUVWXYZ\
         0123456789";
    let mut hash = match hash { Some(s) => s.to_owned(), None => ~"" };
    for s in ss.iter() {
        match *s {
            path_pretty_name(_, extra) => {
                let hi = (extra >> 32) as u32 as uint;
                let lo = extra as u32 as uint;
                hash.push_char(EXTRA_CHARS[hi % EXTRA_CHARS.len()] as char);
                hash.push_char(EXTRA_CHARS[lo % EXTRA_CHARS.len()] as char);
            }
            _ => {}
        }
    }
    if hash.len() > 0 {
        push(hash);
    }
    match vers {
        Some(s) => push(s),
        None => {}
    }

    n.push_char('E'); // End name-sequence.
    n
}

pub fn exported_name(sess: Session,
                     path: path,
                     hash: &str,
                     vers: &str) -> ~str {
    // The version will get mangled to have a leading '_', but it makes more
    // sense to lead with a 'v' b/c this is a version...
    let vers = if vers.len() > 0 && !char::is_XID_start(vers.char_at(0)) {
        "v" + vers
    } else {
        vers.to_owned()
    };

    mangle(sess, path, Some(hash), Some(vers.as_slice()))
}

pub fn mangle_exported_name(ccx: &mut CrateContext,
                            path: path,
                            t: ty::t) -> ~str {
    let hash = get_symbol_hash(ccx, t);
    return exported_name(ccx.sess, path,
                         hash,
                         ccx.link_meta.pkgid.version_or_default());
}

pub fn mangle_internal_name_by_type_only(ccx: &mut CrateContext,
                                         t: ty::t,
                                         name: &str) -> ~str {
    let s = ppaux::ty_to_short_str(ccx.tcx, t);
    let hash = get_symbol_hash(ccx, t);
    return mangle(ccx.sess,
                  ~[path_name(ccx.sess.ident_of(name)),
                    path_name(ccx.sess.ident_of(s))],
                  Some(hash.as_slice()),
                  None);
}

pub fn mangle_internal_name_by_type_and_seq(ccx: &mut CrateContext,
                                            t: ty::t,
                                            name: &str) -> ~str {
    let s = ppaux::ty_to_str(ccx.tcx, t);
    let hash = get_symbol_hash(ccx, t);
    let (_, name) = gensym_name(name);
    return mangle(ccx.sess,
                  ~[path_name(ccx.sess.ident_of(s)), name],
                  Some(hash.as_slice()),
                  None);
}

pub fn mangle_internal_name_by_path_and_seq(ccx: &mut CrateContext,
                                            mut path: path,
                                            flav: &str) -> ~str {
    let (_, name) = gensym_name(flav);
    path.push(name);
    mangle(ccx.sess, path, None, None)
}

pub fn mangle_internal_name_by_path(ccx: &mut CrateContext, path: path) -> ~str {
    mangle(ccx.sess, path, None, None)
}

pub fn output_lib_filename(lm: &LinkMeta) -> ~str {
    format!("{}-{}-{}",
            lm.pkgid.name,
            lm.crate_hash.slice_chars(0, 8),
            lm.pkgid.version_or_default())
}

pub fn get_cc_prog(sess: Session) -> ~str {
    match sess.opts.linker {
        Some(ref linker) => return linker.to_owned(),
        None => {}
    }

    // In the future, FreeBSD will use clang as default compiler.
    // It would be flexible to use cc (system's default C compiler)
    // instead of hard-coded gcc.
    // For win32, there is no cc command, so we add a condition to make it use
    // g++.  We use g++ rather than gcc because it automatically adds linker
    // options required for generation of dll modules that correctly register
    // stack unwind tables.
    match sess.targ_cfg.os {
        abi::OsAndroid => match sess.opts.android_cross_path {
            Some(ref path) => format!("{}/bin/arm-linux-androideabi-gcc", *path),
            None => {
                sess.fatal("need Android NDK path for linking \
                            (--android-cross-path)")
            }
        },
        abi::OsWin32 => ~"g++",
        _ => ~"cc",
    }
}

/// Perform the linkage portion of the compilation phase. This will generate all
/// of the requested outputs for this compilation session.
pub fn link_binary(sess: Session,
                   trans: &CrateTranslation,
                   obj_filename: &Path,
                   out_filename: &Path,
                   lm: &LinkMeta) -> ~[Path] {
    let mut out_filenames = ~[];
    for &output in sess.outputs.iter() {
        let out_file = link_binary_output(sess, trans, output, obj_filename,
                                          out_filename, lm);
        out_filenames.push(out_file);
    }

    // Remove the temporary object file and metadata if we aren't saving temps
    if !sess.opts.save_temps {
        fs::unlink(obj_filename);
        fs::unlink(&obj_filename.with_extension("metadata.o"));
    }

    out_filenames
}

fn is_writeable(p: &Path) -> bool {
    use std::io;

    match io::result(|| p.stat()) {
        Err(..) => true,
        Ok(m) => m.perm & io::UserWrite == io::UserWrite
    }
}

pub fn filename_for_input(sess: &Session, output: session::OutputStyle, lm: &LinkMeta,
                      out_filename: &Path) -> Path {
    let libname = output_lib_filename(lm);
    match output {
        session::OutputRlib => {
            out_filename.with_filename(format!("lib{}.rlib", libname))
        }
        session::OutputDylib => {
            let (prefix, suffix) = match sess.targ_cfg.os {
                abi::OsWin32 => (win32::DLL_PREFIX, win32::DLL_SUFFIX),
                abi::OsMacos => (macos::DLL_PREFIX, macos::DLL_SUFFIX),
                abi::OsLinux => (linux::DLL_PREFIX, linux::DLL_SUFFIX),
                abi::OsAndroid => (android::DLL_PREFIX, android::DLL_SUFFIX),
                abi::OsFreebsd => (freebsd::DLL_PREFIX, freebsd::DLL_SUFFIX),
            };
            out_filename.with_filename(format!("{}{}{}", prefix, libname, suffix))
        }
        session::OutputStaticlib => {
            out_filename.with_filename(format!("lib{}.a", libname))
        }
        session::OutputExecutable => out_filename.clone(),
    }

}

fn link_binary_output(sess: Session,
                      trans: &CrateTranslation,
                      output: session::OutputStyle,
                      obj_filename: &Path,
                      out_filename: &Path,
                      lm: &LinkMeta) -> Path {
    let out_filename = filename_for_input(&sess, output, lm, out_filename);

    // Make sure the output and obj_filename are both writeable.
    // Mac, FreeBSD, and Windows system linkers check this already --
    // however, the Linux linker will happily overwrite a read-only file.
    // We should be consistent.
    let obj_is_writeable = is_writeable(obj_filename);
    let out_is_writeable = is_writeable(&out_filename);
    if !out_is_writeable {
        sess.fatal(format!("Output file {} is not writeable -- check its permissions.",
                           out_filename.display()));
    }
    else if !obj_is_writeable {
        sess.fatal(format!("Object file {} is not writeable -- check its permissions.",
                           obj_filename.display()));
    }

    match output {
        session::OutputRlib => {
            link_rlib(sess, Some(trans), obj_filename, &out_filename);
        }
        session::OutputStaticlib => {
            link_staticlib(sess, obj_filename, &out_filename);
        }
        session::OutputExecutable => {
            link_natively(sess, false, obj_filename, &out_filename);
            // Windows linker will add an ".exe" extension if there was none
            let out_filename = match out_filename.extension() {
                Some(_) => out_filename.clone(),
                None => out_filename.with_extension(win32::EXE_EXTENSION)
            };
            manifest::postprocess_executable(sess, &out_filename);
        }
        session::OutputDylib => {
            link_natively(sess, true, obj_filename, &out_filename);
        }
    }

    out_filename
}

// Create an 'rlib'
//
// An rlib in its current incarnation is essentially a renamed .a file. The
// rlib primarily contains the object file of the crate, but it also contains
// all of the object files from native libraries. This is done by unzipping
// native libraries and inserting all of the contents into this archive.
fn link_rlib(sess: Session,
             trans: Option<&CrateTranslation>, // None == no metadata/bytecode
             obj_filename: &Path,
             out_filename: &Path) -> Archive {
    let mut a = Archive::create(sess, out_filename, obj_filename);

    for &(ref l, kind) in cstore::get_used_libraries(sess.cstore).iter() {
        match kind {
            cstore::NativeStatic => {
                a.add_native_library(l.as_slice());
            }
            cstore::NativeFramework | cstore::NativeUnknown => {}
        }
    }

    // Note that it is important that we add all of our non-object "magical
    // files" *after* all of the object files in the archive. The reason for
    // this is as follows:
    //
    // * When performing LTO, this archive will be modified to remove
    //   obj_filename from above. The reason for this is described below.
    //
    // * When the system linker looks at an archive, it will attempt to
    //   determine the architecture of the archive in order to see whether its
    //   linkable.
    //
    //   The algorithm for this detections is: iterate over the files in the
    //   archive. Skip magical SYMDEF names. Interpret the first file as an
    //   object file. Read architecture from the object file.
    //
    // * As one can probably see, if "metadata" and "foo.bc" were placed
    //   before all of the objects, then the architecture of this archive would
    //   not be correctly inferred once 'foo.o' is removed.
    //
    // Basically, all this means is that this code should not move above the
    // code above.
    match trans {
        Some(trans) => {
            // Instead of putting the metadata in an object file section, rlibs
            // contain the metadata in a separate file.
            let metadata = obj_filename.with_filename(METADATA_FILENAME);
            fs::File::create(&metadata).write(trans.metadata);
            a.add_file(&metadata, false);
            fs::unlink(&metadata);

            // For LTO purposes, the bytecode of this library is also inserted
            // into the archive.
            let bc = obj_filename.with_extension("bc");
            a.add_file(&bc, false);
            if !sess.opts.save_temps {
                fs::unlink(&bc);
            }

            // Now that we've added files, some platforms need us to now update
            // the symbol table in the archive (because some platforms die when
            // adding files to the archive without symbols).
            a.update_symbols();
        }

        None => {}
    }
    return a;
}

// Create a static archive
//
// This is essentially the same thing as an rlib, but it also involves adding
// all of the upstream crates' objects into the the archive. This will slurp in
// all of the native libraries of upstream dependencies as well.
//
// Additionally, there's no way for us to link dynamic libraries, so we warn
// about all dynamic library dependencies that they're not linked in.
//
// There's no need to include metadata in a static archive, so ensure to not
// link in the metadata object file (and also don't prepare the archive with a
// metadata file).
fn link_staticlib(sess: Session, obj_filename: &Path, out_filename: &Path) {
    let mut a = link_rlib(sess, None, obj_filename, out_filename);
    a.add_native_library("morestack");

    let crates = cstore::get_used_crates(sess.cstore, cstore::RequireStatic);
    for &(cnum, ref path) in crates.iter() {
        let name = cstore::get_crate_data(sess.cstore, cnum).name;
        let p = match *path {
            Some(ref p) => p.clone(), None => {
                sess.err(format!("could not find rlib for: `{}`", name));
                continue
            }
        };
        a.add_rlib(&p, name, sess.lto());
        let native_libs = csearch::get_native_libraries(sess.cstore, cnum);
        for &(kind, ref lib) in native_libs.iter() {
            let name = match kind {
                cstore::NativeStatic => "static library",
                cstore::NativeUnknown => "library",
                cstore::NativeFramework => "framework",
            };
            sess.warn(format!("unlinked native {}: {}", name, *lib));
        }
    }
}

// Create a dynamic library or executable
//
// This will invoke the system linker/cc to create the resulting file. This
// links to all upstream files as well.
fn link_natively(sess: Session, dylib: bool, obj_filename: &Path,
                 out_filename: &Path) {
    let tmpdir = TempDir::new("rustc").expect("needs a temp dir");
    // The invocations of cc share some flags across platforms
    let cc_prog = get_cc_prog(sess);
    let mut cc_args = sess.targ_cfg.target_strs.cc_args.clone();
    cc_args.push_all_move(link_args(sess, dylib, tmpdir.path(),
                                    obj_filename, out_filename));
    if (sess.opts.debugging_opts & session::print_link_args) != 0 {
        println!("{} link args: '{}'", cc_prog, cc_args.connect("' '"));
    }

    // May have not found libraries in the right formats.
    sess.abort_if_errors();

    // Invoke the system linker
    debug!("{} {}", cc_prog, cc_args.connect(" "));
    let opt_prog = {
        let _guard = io::ignore_io_error();
        time(sess.time_passes(), "running linker", (), |()|
             run::process_output(cc_prog, cc_args))
    };

    match opt_prog {
        Some(prog) => {
            if !prog.status.success() {
                sess.err(format!("linking with `{}` failed: {}", cc_prog, prog.status));
                sess.note(format!("{} arguments: '{}'", cc_prog, cc_args.connect("' '")));
                sess.note(str::from_utf8_owned(prog.error + prog.output));
                sess.abort_if_errors();
            }
        },
        None => {
            sess.err(format!("could not exec the linker `{}`", cc_prog));
            sess.abort_if_errors();
        }
    }


    // On OSX, debuggers need this utility to get run to do some munging of
    // the symbols
    if sess.targ_cfg.os == abi::OsMacos && sess.opts.debuginfo {
        // FIXME (#9639): This needs to handle non-utf8 paths
        run::process_status("dsymutil",
                            [out_filename.as_str().unwrap().to_owned()]);
    }
}

fn link_args(sess: Session,
             dylib: bool,
             tmpdir: &Path,
             obj_filename: &Path,
             out_filename: &Path) -> ~[~str] {

    // The default library location, we need this to find the runtime.
    // The location of crates will be determined as needed.
    // FIXME (#9639): This needs to handle non-utf8 paths
    let lib_path = sess.filesearch.get_target_lib_path();
    let stage: ~str = ~"-L" + lib_path.as_str().unwrap();

    let mut args = ~[stage];

    // FIXME (#9639): This needs to handle non-utf8 paths
    args.push_all([
        ~"-o", out_filename.as_str().unwrap().to_owned(),
        obj_filename.as_str().unwrap().to_owned()]);

    // When linking a dynamic library, we put the metadata into a section of the
    // executable. This metadata is in a separate object file from the main
    // object file, so we link that in here.
    if dylib {
        let metadata = obj_filename.with_extension("metadata.o");
        args.push(metadata.as_str().unwrap().to_owned());
    }

    if sess.targ_cfg.os == abi::OsLinux {
        // GNU-style linkers will use this to omit linking to libraries which
        // don't actually fulfill any relocations, but only for libraries which
        // follow this flag. Thus, use it before specifing libraries to link to.
        args.push(~"-Wl,--as-needed");

        // GNU-style linkers support optimization with -O. --gc-sections
        // removes metadata and potentially other useful things, so don't
        // include it. GNU ld doesn't need a numeric argument, but other linkers
        // do.
        if sess.opts.optimize == session::Default ||
           sess.opts.optimize == session::Aggressive {
            args.push(~"-Wl,-O1");
        }
    }

    add_local_native_libraries(&mut args, sess);
    add_upstream_rust_crates(&mut args, sess, dylib, tmpdir);
    add_upstream_native_libraries(&mut args, sess);

    // # Telling the linker what we're doing

    if dylib {
        // On mac we need to tell the linker to let this library be rpathed
        if sess.targ_cfg.os == abi::OsMacos {
            args.push(~"-dynamiclib");
            args.push(~"-Wl,-dylib");
            // FIXME (#9639): This needs to handle non-utf8 paths
            args.push(~"-Wl,-install_name,@rpath/" +
                      out_filename.filename_str().unwrap());
        } else {
            args.push(~"-shared")
        }
    }

    if sess.targ_cfg.os == abi::OsFreebsd {
        args.push_all([~"-L/usr/local/lib",
                       ~"-L/usr/local/lib/gcc46",
                       ~"-L/usr/local/lib/gcc44"]);
    }

    // Stack growth requires statically linking a __morestack function
    args.push(~"-lmorestack");

    // FIXME (#2397): At some point we want to rpath our guesses as to
    // where extern libraries might live, based on the
    // addl_lib_search_paths
    args.push_all(rpath::get_rpath_flags(sess, out_filename));

    // Finally add all the linker arguments provided on the command line along
    // with any #[link_args] attributes found inside the crate
    args.push_all(sess.opts.linker_args);
    for arg in cstore::get_used_link_args(sess.cstore).iter() {
        args.push(arg.clone());
    }
    return args;
}

// # Native library linking
//
// User-supplied library search paths (-L on the cammand line) These are
// the same paths used to find Rust crates, so some of them may have been
// added already by the previous crate linking code. This only allows them
// to be found at compile time so it is still entirely up to outside
// forces to make sure that library can be found at runtime.
//
// Also note that the native libraries linked here are only the ones located
// in the current crate. Upstream crates with native library dependencies
// may have their native library pulled in above.
fn add_local_native_libraries(args: &mut ~[~str], sess: Session) {
    for path in sess.opts.addl_lib_search_paths.iter() {
        // FIXME (#9639): This needs to handle non-utf8 paths
        args.push("-L" + path.as_str().unwrap().to_owned());
    }

    let rustpath = filesearch::rust_path();
    for path in rustpath.iter() {
        // FIXME (#9639): This needs to handle non-utf8 paths
        args.push("-L" + path.as_str().unwrap().to_owned());
    }

    for &(ref l, kind) in cstore::get_used_libraries(sess.cstore).iter() {
        match kind {
            cstore::NativeUnknown | cstore::NativeStatic => {
                args.push("-l" + *l);
            }
            cstore::NativeFramework => {
                args.push(~"-framework");
                args.push(l.to_owned());
            }
        }
    }
}

// # Rust Crate linking
//
// Rust crates are not considered at all when creating an rlib output. All
// dependencies will be linked when producing the final output (instead of
// the intermediate rlib version)
fn add_upstream_rust_crates(args: &mut ~[~str], sess: Session,
                            dylib: bool, tmpdir: &Path) {
    // Converts a library file-stem into a cc -l argument
    fn unlib(config: @session::config, stem: &str) -> ~str {
        if stem.starts_with("lib") &&
            config.os != abi::OsWin32 {
            stem.slice(3, stem.len()).to_owned()
        } else {
            stem.to_owned()
        }
    }

    let cstore = sess.cstore;
    if !dylib && !sess.prefer_dynamic() {
        // With an executable, things get a little interesting. As a limitation
        // of the current implementation, we require that everything must be
        // static, or everything must be dynamic. The reasons for this are a
        // little subtle, but as with the above two cases, the goal is to
        // prevent duplicate copies of the same library showing up. For example,
        // a static immediate dependency might show up as an upstream dynamic
        // dependency and we currently have no way of knowing that. We know that
        // all dynamic libaries require dynamic dependencies (see above), so
        // it's satisfactory to include either all static libraries or all
        // dynamic libraries.
        let crates = cstore::get_used_crates(cstore, cstore::RequireStatic);
        if crates.iter().all(|&(_, ref p)| p.is_some()) {
            for (cnum, path) in crates.move_iter() {
                let cratepath = path.unwrap();

                // When performing LTO on an executable output, all of the
                // bytecode from the upstream libraries has already been
                // included in our object file output. We need to modify all of
                // the upstream archives to remove their corresponding object
                // file to make sure we don't pull the same code in twice.
                //
                // We must continue to link to the upstream archives to be sure
                // to pull in native static dependencies. As the final caveat,
                // on linux it is apparently illegal to link to a blank archive,
                // so if an archive no longer has any object files in it after
                // we remove `lib.o`, then don't link against it at all.
                //
                // If we're not doing LTO, then our job is simply to just link
                // against the archive.
                if sess.lto() {
                    let name = cstore::get_crate_data(sess.cstore, cnum).name;
                    time(sess.time_passes(), format!("altering {}.rlib", name),
                         (), |()| {
                        let dst = tmpdir.join(cratepath.filename().unwrap());
                        fs::copy(&cratepath, &dst);
                        let dst_str = dst.as_str().unwrap().to_owned();
                        let mut archive = Archive::open(sess, dst);
                        archive.remove_file(format!("{}.o", name));
                        let files = archive.files();
                        if files.iter().any(|s| s.ends_with(".o")) {
                            args.push(dst_str);
                        }
                    });
                } else {
                    args.push(cratepath.as_str().unwrap().to_owned());
                }
            }
            return;
        }
    }

    // If we're performing LTO, then it should have been previously required
    // that all upstream rust depenencies were available in an rlib format.
    assert!(!sess.lto());

    // This is a fallback of three different  cases of linking:
    //
    // * When creating a dynamic library, all inputs are required to be dynamic
    //   as well
    // * If an executable is created with a preference on dynamic linking, then
    //   this case is the fallback
    // * If an executable is being created, and one of the inputs is missing as
    //   a static library, then this is the fallback case.
    let crates = cstore::get_used_crates(cstore, cstore::RequireDynamic);
    for &(cnum, ref path) in crates.iter() {
        let cratepath = match *path {
            Some(ref p) => p.clone(),
            None => {
                sess.err(format!("could not find dynamic library for: `{}`",
                                 cstore::get_crate_data(sess.cstore, cnum).name));
                return
            }
        };
        // Just need to tell the linker about where the library lives and what
        // its name is
        let dir = cratepath.dirname_str().unwrap();
        if !dir.is_empty() { args.push("-L" + dir); }
        let libarg = unlib(sess.targ_cfg, cratepath.filestem_str().unwrap());
        args.push("-l" + libarg);
    }
}

// Link in all of our upstream crates' native dependencies. Remember that
// all of these upstream native depenencies are all non-static
// dependencies. We've got two cases then:
//
// 1. The upstream crate is an rlib. In this case we *must* link in the
//    native dependency because the rlib is just an archive.
//
// 2. The upstream crate is a dylib. In order to use the dylib, we have to
//    have the dependency present on the system somewhere. Thus, we don't
//    gain a whole lot from not linking in the dynamic dependency to this
//    crate as well.
//
// The use case for this is a little subtle. In theory the native
// dependencies of a crate a purely an implementation detail of the crate
// itself, but the problem arises with generic and inlined functions. If a
// generic function calls a native function, then the generic function must
// be instantiated in the target crate, meaning that the native symbol must
// also be resolved in the target crate.
fn add_upstream_native_libraries(args: &mut ~[~str], sess: Session) {
    let cstore = sess.cstore;
    cstore::iter_crate_data(cstore, |cnum, _| {
        let libs = csearch::get_native_libraries(cstore, cnum);
        for &(kind, ref lib) in libs.iter() {
            match kind {
                cstore::NativeUnknown => args.push("-l" + *lib),
                cstore::NativeFramework => {
                    args.push(~"-framework");
                    args.push(lib.to_owned());
                }
                cstore::NativeStatic => {
                    sess.bug("statics shouldn't be propagated");
                }
            }
        }
    });
}