How does gcov get the gcda file at runtime? - gcc

Question

I want dumping gcov data at runtime.
I build a libgcov_preload.so using file with the following code：
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
extern void __gcov_flush();
void sighandler(int signo)
{
printf("prepare invkoe __gcov_flush");
__gcov_flush(); /* flush out gcov stats data */
printf("invkoe __gcov_flush complete");
// raise(signo); /* raise the signal again to crash process */
}
__attribute__((constructor))
void
ctor()
{
struct sigaction sa;
/* setup signal hander */
sa.sa_handler = sighandler;
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_RESTART;
if (sigaction(SIGUSR1, &sa, NULL) == -1) {
perror("Could not set signal handler");
}
}
the build command is: gcc -shared -fpic gcov_preload.c -o libgcov_preload.so
and I have a test program as blow:
#include <unistd.h>
#include <stdio.h>
int main()
{
printf("test program started \n");
while(1)
{
sleep(1);
}
return 0;
}
the build command is: gcc -fprofile-arcs -ftest-coverage main_test.c -o main_test
and start main_test with: LD_PRELOAD=./libgcov_preload.so ./main_test
using killall -USR1 main_test send signal to generate gcda file.
but I get error
./main_test: symbol lookup error: ./libgcov_preload.so: undefined symbol: __gcov_flush
I don't know what's wrong.
the gcc version information:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/8/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,objc,obj-c++,ada,go,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl --enable-libmpx --enable-offload-targets=nvptx-none --without-cuda-driver --enable-gnu-indirect-function --with-tune=generic --with-arch_32=x86-64 --build=x86_64-redhat-linux
Thread model: posix
gcc version 8.5.0 20210514 (Red Hat 8.5.0-4) (GCC)