On Mon, 2023-06-19 at 15:55 +0200, Florent Revest wrote:
On Mon, Jun 19, 2023 at 1:20 PM Florent Revest revest@chromium.org wrote:
On Thu, Jun 15, 2023 at 7:05 PM Eduard Zingerman eddyz87@gmail.com wrote:
On Thu, 2023-06-15 at 17:44 +0200, Florent Revest wrote:
An easy reproducer is:
$ touch pwet.c
$ clang -g -fsanitize=kernel-address -c -o pwet.o pwet.c $ llvm-dwarfdump pwet.o | grep module_ctor
$ clang -fno-integrated-as -g -fsanitize=kernel-address -c -o pwet.o pwet.c $ llvm-dwarfdump pwet.o | grep module_ctor DW_AT_name ("asan.module_ctor")
Interestingly, I am unable to reproduce it using either clang version 14.0.0-1ubuntu1 or clang main (bd66f4b1da30).
Somehow, I didn't think of trying other clang versions! Thanks, that's a good point Eduard. :)
I also can't reproduce it on a 14x build.
However, I seem to be able to reproduce it on main:
git clone https://github.com/llvm/llvm-project.git mkdir llvm-project/build cd llvm-project/build git checkout bd66f4b1da30 cmake -DLLVM_ENABLE_PROJECTS=clang -DCMAKE_BUILD_TYPE=Release -G "Unix Makefiles" ../llvm make -j $(nproc)
bin/clang -fno-integrated-as -g -fsanitize=kernel-address -c -o ~/pwet.o ~/pwet.c bin/llvm-dwarfdump ~/pwet.o | grep module_ctor # Shows module_ctor
I started a bisection, hopefully that will point to something interesting
The bisection pointed to a LLVM patch from Nick in October 2022: e3bb359aacdd ("[clang][Toolchains][Gnu] pass -g through to assembler")
Based on the context I have, that commit sounds fair enough. I don't think LLVM does anything wrong here, it seems like BPF should be the one dealing with dots in function debug info.
That explains why I could not reproduce the issue: I tried with gas 2.38. Using gas 2.40 I see the same behavior as you.
If one tries to generate assembly file with '-fsanitize':
$ clang -fno-integrated-as -g -fsanitize=kernel-address -S -o pwet.s pwet.c $ cat pwet.s .text .file "pwet.c" .p2align 4, 0x90 # -- Begin function asan.module_ctor .type asan.module_ctor,@function asan.module_ctor: # @asan.module_ctor .Lfunc_begin0: ...
And then compile it using Gnu assembler:
$ as --64 -o pwet.o pwet.s -g -gdwarf-5
The behavior differs between 2.38 and 2.40, the older version does not produce debug entry for 'asan.module_ctor', while newer does.