[llvm-dev] llvm-cov: Combined report for multiple executables

[Vedant Kumar via llvm-dev]

Hi Sadrul,

> On Mar 8, 2018, at 7:40 PM, Sadrul Chowdhury via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi! I am trying to get a combined coverage report from multiple
> executables. Looking at earlier discussions [1, 2], it looks like this
> is supposed to work. I am having some difficulty getting this to work
> as I would expect it to work, however. Following is a simple case to
> explain:
> 
> ////////// shared.h
> #include <string>
> 
> void Print1(const std::string& msg);
> void Print2(const std::string& msg);
> ////////// end
> 
> ////////// shared.cc
> #include <iostream>
> #include <string>
> 
> void Print1(const std::string& msg) {
>  std::cout << "1" << msg;
> }
> 
> void Print2(const std::string& msg) {
>  std::cout << "2" << msg;
> }
> ////////// end
> 
> ////////// first.cc
> #include "shared.h"
> 
> int main() {
>  Print1("First\n");
>  return 0;
> }
> ////////// end
> 
> ////////// second.cc
> #include "shared.h"
> 
> int main() {
>  Print2("Second\n");
>  return 0;
> }
> ////////// end
> 
> I use the following commands to build 'first' and 'second' binaries:
>  clang++ -O0 -c -fprofile-instr-generate -fcoverage-mapping shared.cc
> -o ./out/shared.o
>  clang++ -O0 -fprofile-instr-generate -fcoverage-mapping
> ./out/shared.o first.cc -o ./out/first
>  clang++ -O0 -fprofile-instr-generate -fcoverage-mapping
> ./out/shared.o second.cc -o ./out/second
> 
> I then use the following to run the binaries:
>  LLVM_PROFILE_FILE='./out/first.profraw' ./out/first
>  LLVM_PROFILE_FILE='./out/second.profraw' ./out/second
> 
> I then use the following commands to show the report:
>  llvm-profdata merge -sparse ./out/first.profraw ./out/second.profraw
> -o ./out/all.profdata
>  llvm-cov show ./out/second -object ./out/first -instr-profile
> ./out/all.profdata
> 
> But the output only contains:
> 
> second.cc:
>    1|       |#include "shared.h"
>    2|       |
>    3|      2|int main() {
>    4|      2|  Print2("Second\n");
>    5|      2|  return 0;
>    6|      2|}
> 
> shared.cc:
>    1|       |#include <iostream>
>    2|       |#include <string>
>    3|       |
>    4|      1|void Print1(const std::string& msg) {
>    5|      1|  std::cout << "1" << msg;
>    6|      1|}
>    7|       |
>    8|      1|void Print2(const std::string& msg) {
>    9|      1|  std::cout << "2" << msg;
>   10|      1|}
> 
> The output does not include anything for first.cc If I run the last
> command with ./out/second and ./out/first swapped, then the output
> only contains first.cc and shared.cc, but does not have second.cc
> 
> Is my expectation that the report should include both first.cc and
> second.cc correct? If it is, then I am probably holding something
> wrong? Any suggestions on what I should try?

The coverage tool currently has limitations which require it to assume that the one definition rule holds over all of the tool inputs. That means that if you have multiple definitions of the same symbol (in this case "main"), the coverage tool will only report one of them.

You might try reorganizing the code so that there's only one function called main.

best,
vedant


> 
> [1] https://groups.google.com/forum/#!msg/llvm-dev/11mEQr1t2ys/9SOI39v-AAAJ;context-place=forum/llvm-dev
> [2] https://reviews.llvm.org/D25086#change-SchnPUmKhFiN
> 
> Thank you!
> Sadrul
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