close()x86_64系统调用奇怪的返回值

Question

内核升级后,我的xinetd守护进程突然停止工作(从2.6.24到2.6.33).我跑了一个strace,发现了这个:

[...]
close(3)                                = 0
munmap(0x7f1a93b43000, 4096)            = 0
getrlimit(RLIMIT_NOFILE, {rlim_cur=8*1024, rlim_max=16*1024}) = 0
setrlimit(RLIMIT_NOFILE, {rlim_cur=1024, rlim_max=1024}) = 0
close(3)                                = 4294967287
exit_group(1)                           = ?

所以基本上,看起来close系统调用返回的东西不同于0或-1

我做了几次测试,看起来它只发生在64位可执行文件中:

$ file closetest32
closetest32: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically linked, not stripped
$ strace closetest32
execve("./closetest32", ["closetest32"], [/* 286 vars */]) = 0
[ Process PID=4731 runs in 32 bit mode. ]
open("/proc/mounts", O_RDONLY)          = 3
close(3)                                = 0
close(3)                                = -1 EBADF (Bad file descriptor)
_exit(0)                                = ?


$ file closetest64
closetest64: ELF 64-bit LSB executable, AMD x86-64, version 1 (SYSV), statically linked, not stripped
$ strace closetest64
execve("./closetest64", ["closetest64"], [/* 286 vars */]) = 0
open("/proc/mounts", O_RDONLY)          = 3
close(3)                                = 0
close(3)                                = 4294967287
_exit(0)                                = ?

我正在运行以下内核:

Linux foobar01 2.6.33.9-rt31.64.el5rt #1 SMP PREEMPT RT Wed May 4 10:34:12 EDT 2011 x86_64 x86_64 x86_64 GNU/Linux

最糟糕的是我无法在具有相同内核的另一台机器上重现该错误.

有任何想法吗 ？

编辑:根据要求:这是用于closetest32和closetest64的代码

closetest32.asm:

.section .data

filename:
    .ascii "/proc/mounts"

.section .text
.globl _start
_start:
    xorl %edi, %edi
    movl $5, %eax # open() i386 system call
    leal filename, %ebx # %ebx ---> filename
    movl $0, %esi # O_RDONLY flag into esi
    int $0x80

    xorl %edi, %edi
    movl $6, %eax # close() i386 system call
    movl $3, %ebx # fd 3
    int $0x80

    xorl %edi, %edi
    movl $6, %eax # close() i386 system call
    movl $3, %ebx # fd 3
    int $0x80

    ## terminate program via _exit () system call
    movl $1, %eax # %eax =  _exit() i386 system call
    xorl %ebx, %ebx # %ebx = 0 normal program return code
    int $0x80

编译为:

as test32.asm -o test32.o --32
ld -m elf_i386 test32.o -o closetest32

closetest64.asm:

.section .data

filename:
    .ascii "/proc/mounts"

.section .text
.globl _start
_start:
    xorq %rdi, %rdi
    movq $2, %rax # open() system call
    leaq filename, %rdi # %rdi ---> filename
    movq $0, %rsi # O_RDONLY flag into rsi
    syscall

    xorq %rdi, %rdi
    movq $3, %rax # close() system call
    movq $3, %rdi # fd 3
    syscall

    xorq %rdi, %rdi
    movq $3, %rax # close() system call
    movq $3, %rdi # fd 3
    syscall

    ## terminate program via _exit () system call
    movq $60, %rax # %rax = _exit() system call
    xorq %rdi, %rdi # %rdi = 0 normal program return code
    syscall

汇编:

as test64.asm -o test64.o
ld test64.o -o closetest64

Answer 1

正如预期的那样，回滚到以前的内核版本解决了该问题。我并不是真正的内核专家，但据我了解，@R.. 给出的答案是有道理的：

这是 64 位机器，因此 1<<32-9 不应出现。问题是内核在内部使用 unsigned 而不是 int 作为其中一些函数的返回值，然后返回 -EBADF，它会减少模 2^32 而不是模 2^64

问题是，在进行比较以查看它是否是一个小负数时，处理系统调用错误返回的 libc 系统调用包装器中的通用代码必须将返回值视为 long （因为它可能是指针或某些系统调用的 long）指示错误的值。但内核返回的 (long)(unsigned)-9 与 (long)-9 有很大不同。或 (unsigned long)-9 （其中任何一个都可以）。