Hi,
I am trying to instrument a very simple code with clang. The code is as following:
#include <iostream>
int sub(int x) { return x - 2;}
int main() {
std::cout<<sub(2)<<std::end;
return 0;
}
I try to compile the code with clang++-12 -O0 ./test.cpp -Xclang -fprofile-instrument=llvm -Xclang -fprofile-instrument-path=./test.profraw. The compilation works and generates an object file with the following symbols:
SYMBOL TABLE:
00000000004002a8 l d .interp 0000000000000000 .interp
00000000004002c4 l d .note.gnu.build-id 0000000000000000 .note.gnu.build-id
00000000004002e8 l d .note.ABI-tag 0000000000000000 .note.ABI-tag
0000000000400308 l d .gnu.hash 0000000000000000 .gnu.hash
0000000000400338 l d .dynsym 0000000000000000 .dynsym
0000000000400428 l d .dynstr 0000000000000000 .dynstr
0000000000400530 l d .gnu.version 0000000000000000 .gnu.version
0000000000400548 l d .gnu.version_r 0000000000000000 .gnu.version_r
0000000000400588 l d .rela.dyn 0000000000000000 .rela.dyn
00000000004005d0 l d .rela.plt 0000000000000000 .rela.plt
0000000000401000 l d .init 0000000000000000 .init
0000000000401020 l d .plt 0000000000000000 .plt
0000000000401090 l d .text 0000000000000000 .text
00000000004012f8 l d .fini 0000000000000000 .fini
0000000000402000 l d .rodata 0000000000000000 .rodata
0000000000402034 l d __llvm_prf_names 0000000000000000 __llvm_prf_names
0000000000402094 l d .eh_frame_hdr 0000000000000000 .eh_frame_hdr
00000000004020e8 l d .eh_frame 0000000000000000 .eh_frame
0000000000403dd8 l d .init_array 0000000000000000 .init_array
0000000000403de8 l d .fini_array 0000000000000000 .fini_array
0000000000403df0 l d .dynamic 0000000000000000 .dynamic
0000000000403ff0 l d .got 0000000000000000 .got
0000000000404000 l d .got.plt 0000000000000000 .got.plt
0000000000404048 l d .data 0000000000000000 .data
0000000000404058 l d __llvm_prf_cnts 0000000000000000 __llvm_prf_cnts
0000000000404078 l d __llvm_prf_data 0000000000000000 __llvm_prf_data
0000000000404140 l d .bss 0000000000000000 .bss
0000000000000000 l d .comment 0000000000000000 .comment
0000000000000000 l df *ABS* 0000000000000000 test.cpp
00000000004010e0 l F .text 000000000000001f _GLOBAL__sub_I_test.cpp
0000000000404251 l O .bss 0000000000000001 _ZStL8__ioinit
0000000000401090 l F .text 000000000000004c __cxx_global_var_init
0000000000000000 l df *ABS* 0000000000000000 crtstuff.c
0000000000401140 l F .text 0000000000000000 deregister_tm_clones
0000000000401170 l F .text 0000000000000000 register_tm_clones
00000000004011b0 l F .text 0000000000000000 __do_global_dtors_aux
0000000000404250 l O .bss 0000000000000001 completed.0
0000000000403de8 l O .fini_array 0000000000000000 __do_global_dtors_aux_fini_array_entry
00000000004011e0 l F .text 0000000000000000 frame_dummy
0000000000403dd8 l O .init_array 0000000000000000 __frame_dummy_init_array_entry
0000000000000000 l df *ABS* 0000000000000000 crtstuff.c
000000000040222c l O .eh_frame 0000000000000000 __FRAME_END__
0000000000000000 l df *ABS* 0000000000000000
0000000000402094 l .eh_frame_hdr 0000000000000000 __GNU_EH_FRAME_HDR
0000000000403df0 l O .dynamic 0000000000000000 _DYNAMIC
0000000000403de8 l .init_array 0000000000000000 __init_array_end
0000000000403dd8 l .init_array 0000000000000000 __init_array_start
0000000000404000 l O .got.plt 0000000000000000 _GLOBAL_OFFSET_TABLE_
0000000000404138 g __llvm_prf_data 0000000000000000 _edata
0000000000404048 w .data 0000000000000000 data_start
0000000000402000 g O .rodata 0000000000000004 _IO_stdin_used
0000000000401220 g F .text 000000000000005c main
0000000000401030 F *UND* 0000000000000000 _ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_@@GLIBCXX_3.4
0000000000404050 g O .data 0000000000000000 .hidden __dso_handle
00000000004012f8 g F .fini 0000000000000000 .hidden _fini
0000000000401130 g F .text 0000000000000005 .hidden _dl_relocate_static_pie
0000000000000000 F *UND* 0000000000000000 __cxa_atexit@@GLIBC_2.2.5
0000000000402008 g O .rodata 0000000000000008 __llvm_profile_raw_version
0000000000402010 g O .rodata 0000000000000024 __llvm_profile_filename
0000000000401100 g F .text 000000000000002f _start
0000000000000000 F *UND* 0000000000000000 _ZNSolsEPFRSoS_E@@GLIBCXX_3.4
0000000000401000 g F .init 0000000000000000 .hidden _init
0000000000404058 g O __llvm_prf_cnts 0000000000000000 .hidden __TMC_END__
0000000000404140 g O .bss 0000000000000110 _ZSt4cout@@GLIBCXX_3.4
0000000000404048 g .data 0000000000000000 __data_start
0000000000404258 g .bss 0000000000000000 _end
0000000000404138 g .bss 0000000000000000 __bss_start
0000000000000000 F *UND* 0000000000000000 _ZNSt8ios_base4InitC1Ev@@GLIBCXX_3.4
0000000000401280 g F .text 0000000000000065 __libc_csu_init
00000000004011f0 g F .text 0000000000000023 _Z3subi
0000000000000000 F *UND* 0000000000000000 _ZNSolsEi@@GLIBCXX_3.4
00000000004012f0 g F .text 0000000000000005 __libc_csu_fini
0000000000000000 F *UND* 0000000000000000 __libc_start_main@@GLIBC_2.2.5
0000000000000000 w *UND* 0000000000000000 __gmon_start__
0000000000401080 F *UND* 0000000000000000 _ZNSt8ios_base4InitD1Ev@@GLIBCXX_3.4
From the symbols, it looks like it does work since it inserts __llvm_prf_data and the related functions for instrumentation. However, I can’t find the test.profraw file generated. Even if I pre-create the file, no content is written to the file.
I wonder if I miss anything in order to retrieve the instrumentation results. I appreciate any comment on this issue. Thank you so much!
Edit: I found that I can get the instrumentation results with clang++-12 -O0 /home/devkon/clang-exp/test.cpp -fprofile-generate=./test.profraw. I know that without -Xclang, we are using clang as a driver and it invokes a binary executable. However, what I would like to do is to use the clang frontend compiler for instrumentation. Is there anything I am missing? Or for the current situation the clang frontend compiler (compiler instance) simply doesn’t support the instrumentation?