[LLVMdev] Coverage mapping issue: Malformed profile data

[Justin Bogner]

Dmitry Volyntsev <xeioexception at gmail.com> writes:
> It seems I came across on issue with coverage mapping
> (http://www.llvm.org/docs/CoverageMappingFormat.html)
>
> check on:
> llvm revision: r228136
> clang  Last Changed Rev: 228121
> build: Debug+Asserts
> OS: ubuntu 14.04
>
>
> Here is simple snippets
>
> test1.c: NOT OK
> ==================
> #include <stdio.h>
>
> static int foo() { return 42; }
> int main() {
>  return 0;
> }
> ==================
> cp src/test1.c src/test.c; rm -fr default.profraw test.profdata ;
> clang -c -o obj/test.o src/test.c -I -g -O0 -fprofile-instr-generate
> -fcoverage-mapping; clang -o bin/test obj/test.o -I -g -O0
> -fprofile-instr-generate -fcoverage-mapping; ./bin/test ;
> llvm-profdata merge -o test.profdata default.profraw; llvm-cov show
> ./bin/test -instr-profile=test.profdata
>
> error: Failed to load coverage: Malformed profile data
>
>
>
> test2.c: OK
> ==================
> #include <stdio.h>
>
> static int foo() { return 42; }
> int main() {
>  return foo();
> }
> ==================
> cp src/test2.c src/test.c; rm -fr default.profraw test.profdata ;
> clang -c -o obj/test.o src/test.c -I -g -O0 -fprofile-instr-generate
> -fcoverage-mapping; clang -o bin/test obj/test.o -I -g -O0
> -fprofile-instr-generate -fcoverage-mapping; ./bin/test ;
> llvm-profdata merge -o test.profdata default.profraw; llvm-cov show
> ./bin/test -instr-profile=test.profdata
>
> /home/xeioex/workspace/clang/experiments/llvm-cov/test/src/test.c:
>        |    1|#include <stdio.h>
>        |    2|
>       1|    3|static int foo() { return 42; }
>       1|    4|int main() {
>       1|    5|  return foo();
>       1|    6|}
>
> test3.c: OK
> ==================
> #include <stdio.h>
>
> int foo() { return 42; }
> int main() {
>  return 0;
> }
> ==================
> cp src/test3.c src/test.c; rm -fr default.profraw test.profdata ;
> clang -c -o obj/test.o src/test.c -I -g -O0 -fprofile-instr-generate
> -fcoverage-mapping; clang -o bin/test obj/test.o -I -g -O0
> -fprofile-instr-generate -fcoverage-mapping; ./bin/test ;
> llvm-profdata merge -o test.profdata default.profraw; llvm-cov show
> ./bin/test -instr-profile=test.profdata
>
> /home/xeioex/workspace/clang/experiments/llvm-cov/test/src/test.c:
>        |    1|#include <stdio.h>
>        |    2|
>       0|    3|int foo() { return 42; }
>       1|    4|int main() {
>       1|    5|  return 0;
>       1|    6|}
>
>
> As far I can understand issue somehow related to unused static functions.

It looks like this hits when a function isn't emitted by the frontend
but we emit an "empty" coverage map for it.

> Also, as I can track down the problem raised because of
> lib/ProfileData/CoverageMappingReader.cpp (SectionData::get) expects
> that function's names located inside __llvm_prf_names section but it
> not true in case of test1.c, instead some function names located
> inside .rodata section.

The problem is that these don't go through the InstrProfiling machinery,
so the names aren't lowered properly. I'd noticed a related issue not
long ago, but fixed a bug by inspection that happened to hide it
(r226764).

Feel free to file a bug (http://llvm.org/bugs/) and I'll to get this
fixed in the next day or two.