Instrument C / C++ in MemorySanitizer example

Modify the example to instrument C / C++ in addition to Rust, since it
will be generally required (e.g., when using libbacktrace for symbolication).

Additionally use rustc specific flag to track the origins of unitialized
memory rather than LLVM one.

diff --git a/src/doc/unstable-book/src/compiler-flags/sanitizer.md b/src/doc/unstable-book/src/compiler-flags/sanitizer.md
index cbb90bd3bb3316512f357e24add4366dbb88c2ec..c799374354b3ed0ebdec57774010fb413be2defd 100644 (file)
--- a/src/doc/unstable-book/src/compiler-flags/sanitizer.md
+++ b/src/doc/unstable-book/src/compiler-flags/sanitizer.md
@@ -96,7 +96,7 @@ Shadow byte legend (one shadow byte represents 8 application bytes):
 ## MemorySanitizer
 
 Use of uninitialized memory. Note that we are using `-Zbuild-std` to instrument
-standard library, and passing `-msan-track-origins=2` to the LLVM to track
+the standard library, and passing `-Zsanitizer-track-origins` to track the
 origins of uninitialized memory:
 
 ```shell
@@ -111,7 +111,15 @@ fn main() {
     }
 }
 
-$ env RUSTFLAGS="-Zsanitizer=memory -Cllvm-args=-msan-track-origins=2" cargo -Zbuild-std run --target x86_64-unknown-linux-gnu
+$ export \
+  CC=clang \
+  CXX=clang++ \
+  CFLAGS='-fsanitize=memory -fsanitize-memory-track-origins' \
+  CXXFLAGS='-fsanitize=memory -fsanitize-memory-track-origins' \
+  RUSTFLAGS='-Zsanitizer=memory -Zsanitizer-memory-track-origins' \
+  RUSTDOCFLAGS='-Zsanitizer=memory -Zsanitizer-memory-track-origins'
+$ cargo clean
+$ cargo -Zbuild-std run --target x86_64-unknown-linux-gnu
 ==9416==WARNING: MemorySanitizer: use-of-uninitialized-value
     #0 0x560c04f7488a in core::fmt::num::imp::fmt_u64::haa293b0b098501ca $RUST/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/src/rust/src/libcore/fmt/num.rs:202:16
 ...