[libfuzzer] Add "Symbolization" and "Debugging" sections to reproducing.md page.

testing/libfuzzer/reproducing.md

Index: testing/libfuzzer/reproducing.md
diff --git a/testing/libfuzzer/reproducing.md b/testing/libfuzzer/reproducing.md
index 8072cec5363871ab4a8c97d4a596d7280b6bd42c..817b8a50ff00ce5afb11f7e440509ccf7b5620be 100644
--- a/testing/libfuzzer/reproducing.md
+++ b/testing/libfuzzer/reproducing.md
@@ -86,3 +86,31 @@ $ export UBSAN_OPTIONS=halt_on_error=1:print_stacktrace=1
 $ out/libfuzzer/$FUZZER_NAME /path/to/repro
 ```
 
+### Symbolization
+
+Memory tools (ASan, MSan, UBSan) use [llvm-symbolizer] binary from the Clang
+distribution to symbolize the stack traces. To get a symbolized crash report,
+make sure `llvm-symbolizer` is in `PATH` or provide it in separate

[Nico, 2016/08/29 12:04:13]

Mention that llvm-symbolizer is in third_party/llvm-build/Release+Asserts/bin
and/or that it's copied to the build dir at build time (and make the example
point there)

[mmoroz, 2016/08/29 12:40:00]

Done.

+`ASAN_SYMBOLIZER_PATH` environment variable:
+
+```bash
+$ export ASAN_SYMBOLIZER_PATH=/path/to/llvm_build/bin/llvm-symbolizer
+$ out/libfuzzer/$FUZZER_NAME /path/to/repro
+```
+
+The same approach works for `MSAN_SYMBOLIZER_PATH` and `UBSAN_SYMBOLIZER_PATH`.
+
+Additional information regarding symbolization is available in sanitizers
+documentation: [AddressSanitizerCallStack].
+
+
+### Debugging
+
+Please checkout [AddressSanitizerAndDebugger] page for some tips on debugging of

[Nico, 2016/08/29 12:04:13]

s/checkout/look at/ since "checkout" sounds like `svn checkout`. (Also,
"checkout" is the noun, while the verb is "check out" with a space).

Doesn't abort_on_error work in ASAN_OPTIONS as well?

[mmoroz, 2016/08/29 12:40:00]

Thanks for the explanation! My bad.

abort_on_error works for ASan too. My intention was to do not write about that,
since the link contains that information. But probably it's worth to be
mentioned here. Done.

+binaries built with ASan. For binaries built with MSan,
+`MSAN_OPTIONS=abort_on_error=1` makes gdb to stop after the report.
+
+
+[AddressSanitizerAndDebugger]: https://github.com/google/sanitizers/wiki/AddressSanitizerAndDebugger
+[AddressSanitizerCallStack]: https://github.com/google/sanitizers/wiki/AddressSanitizerCallStack
+[llvm-symbolizer]: http://llvm.org/docs/CommandGuide/llvm-symbolizer.html