Re: [PATCH 2/5] x86: ret_from_fork - get rid of jump back

[Cyrill Gorcunov <gorcunov@gmail.com>]

[Ingo Molnar - Thu, Nov 27, 2008 at 02:41:21PM +0100]
| 
| * Cyrill Gorcunov <gorcunov@gmail.com> wrote:
| 
...
| 
| Could you test something like the patch attached below, which cleans 
| up this code and applies the code reduction and speedup? Warning: 
| completely untested! Please check that things like strace -f and gdb 
| attaching to forked tasks still works fine. (it should by all means)
| 
| Thanks,
| 
| 	Ingo

Ingo, I found 2.6.26 test machine where I've patched the entry_64.S
in a manner you pointed. So here is a test program and strace output.
Seems all works fine. Didn't check "audit" code which I simply don't
know how to be done.
 
		- Cyrill -
---

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
	int pid;

	pid = fork();

	if (pid < 0) {
		fprintf(stderr, "Fork failed!\n");
		exit(-1);
	}

	else if (pid == 0) {
		printf("I am the child, return from fork=%d\n", pid);
	} else {
	  printf("I am the parent, return from fork, child pid=%d\n", pid);
	  printf("Parent exiting!\n");
	  exit(0);
	}
}
---

5897  execve("./main", ["./main"], [/* 18 vars */]) = 0
5897  brk(0)                            = 0x2514000
5897  mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa0e517f000
5897  access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
5897  mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa0e517d000
5897  access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
5897  open("/etc/ld.so.cache", O_RDONLY) = 3
5897  fstat(3, {st_mode=S_IFREG|0644, st_size=48530, ...}) = 0
5897  mmap(NULL, 48530, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fa0e5171000
5897  close(3)                          = 0
5897  access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
5897  open("/lib/libc.so.6", O_RDONLY)  = 3
5897  read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\220\345"..., 832) = 832
5897  fstat(3, {st_mode=S_IFREG|0755, st_size=1502520, ...}) = 0
5897  mmap(NULL, 3609304, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa0e4bf0000
5897  mprotect(0x7fa0e4d59000, 2093056, PROT_NONE) = 0
5897  mmap(0x7fa0e4f58000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x168000) = 0x7fa0e4f58000
5897  mmap(0x7fa0e4f5d000, 17112, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fa0e4f5d000
5897  close(3)                          = 0
5897  mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa0e5170000
5897  mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa0e516f000
5897  arch_prctl(ARCH_SET_FS, 0x7fa0e516f6e0) = 0
5897  mprotect(0x7fa0e4f58000, 16384, PROT_READ) = 0
5897  mprotect(0x7fa0e5180000, 4096, PROT_READ) = 0
5897  munmap(0x7fa0e5171000, 48530)     = 0
5897  clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fa0e516f770) = 5898
5897  fstat(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(5, 1), ...}) = 0
5898  fstat(1,  <unfinished ...>
5897  ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS <unfinished ...>
5898  <... fstat resumed> {st_mode=S_IFCHR|0600, st_rdev=makedev(5, 1), ...}) = 0
5897  <... ioctl resumed> , {B38400 opost isig icanon echo ...}) = 0
5897  mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0 <unfinished ...>
5898  ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS <unfinished ...>
5897  <... mmap resumed> )              = 0x7fa0e517c000
5898  <... ioctl resumed> , {B38400 opost isig icanon echo ...}) = 0
5897  write(1, "I am the parent, return from for"..., 50 <unfinished ...>
5898  mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0 <unfinished ...>
5897  <... write resumed> )             = 50
5898  <... mmap resumed> )              = 0x7fa0e517c000
5897  write(1, "Parent exiting!\n", 16 <unfinished ...>
5898  write(1, "I am the child, return from fork"..., 35 <unfinished ...>
5897  <... write resumed> )             = 16
5898  <... write resumed> )             = 35
5897  exit_group(0)                     = ?
5898  exit_group(0)                     = ?
---