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    SubjectRe: [PATCH 2/5] x86: ret_from_fork - get rid of jump back
    [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) = ?
    ---


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