tracy/extra/systrace/tracy_systrace.c

66 lines
2.0 KiB
C

#include <fcntl.h>
#include <poll.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <dlfcn.h>
enum { BufSize = 64*1024 };
typedef int (*open_t)( const char*, int, ... );
typedef void (*exit_t)( int );
typedef int (*poll_t)( struct pollfd*, nfds_t, int timeout );
typedef int (*nanosleep_t)( const struct timespec*, struct timespec* );
typedef ssize_t (*read_t)( int, void*, size_t );
typedef ssize_t (*write_t)( int, const void*, size_t );
void _start()
{
void* libc = dlopen( "libc.so", RTLD_LAZY );
open_t sym_open = dlsym( libc, "open" );
exit_t sym_exit = dlsym( libc, "exit" );
poll_t sym_poll = dlsym( libc, "poll" );
nanosleep_t sym_nanosleep = dlsym( libc, "nanosleep" );
read_t sym_read = dlsym( libc, "read" );
write_t sym_write = dlsym( libc, "write" );
char buf[BufSize];
int kernelFd = sym_open( "/sys/kernel/debug/tracing/trace_pipe", O_RDONLY );
if( kernelFd < 0 ) sym_exit( 0 );
struct pollfd pfd_in;
pfd_in.fd = kernelFd;
pfd_in.events = POLLIN | POLLERR;
struct pollfd pfd_out;
pfd_out.fd = STDOUT_FILENO;
pfd_out.events = POLLERR;
struct timespec sleepTime;
sleepTime.tv_sec = 0;
sleepTime.tv_nsec = 1000 * 1000 * 10;
// While the pipe is open (no POLLERR on the output fd)
while( sym_poll( &pfd_out, 1, 0) <= 0 )
{
// If there is neither data (POLLIN) nor an error (POLLERR) on
// the read fd, sleep. This implements a blocking read without relying
// on the Linux kernel's implementation of blocking reads which causes
// a large number of context switches.
if( sym_poll( &pfd_in, 1, 0 ) <= 0 ) {
sym_nanosleep( &sleepTime, NULL );
continue; // go back to the while condition polling the output fd
}
const ssize_t rd = sym_read( kernelFd, buf, BufSize );
if( rd <= 0 ) break;
sym_write( STDOUT_FILENO, buf, rd );
}
sym_exit( 0 );
}