关于APUE书中讲的setjmp和longjmp

BLZer

示例程序来自apue2的7.13,程序如下

#include "apue.h" #include <setjmp.h> static void f1(int, int, int, int); static void f2(void); static jmp_buf jmpbuffer; static int     globval; int main(void) { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int             autoval; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;register int    regival; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;volatile int    volaval; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;static int      statval; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;globval = 1; autoval = 2; regival = 3; volaval = 4; statval = 5; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (setjmp(jmpbuffer) != 0) { &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("after longjmp:\n"); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("globval = %d, autoval = %d, regival = %d," &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;" volaval = %d, statval = %d\n", &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;globval, autoval, regival, volaval, statval); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;exit(0); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/* &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;* Change variables after setjmp, but before longjmp. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;*/ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;globval = 95; autoval = 96; regival = 97; volaval = 98; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;statval = 99; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;f1(autoval, regival, volaval, statval); /* never returns */ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;exit(0); } static void f1(int i, int j, int k, int l) { &nbsp;&nbsp;&nbsp;&nbsp;printf("in f1():\n"); &nbsp;&nbsp;&nbsp;&nbsp;printf("globval = %d, autoval = %d, regival = %d," &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;" volaval = %d, statval = %d\n", globval, i, j, k, l); &nbsp;&nbsp;&nbsp;&nbsp;f2(); } static void f2(void) { &nbsp;&nbsp;&nbsp;&nbsp;longjmp(jmpbuffer, 1); }

用gcc 编译后,运行结果是:

  $ ./a.out
    in f1():
    globval = 95, autoval = 96, regival = 97, volaval = 98, statval = 99
    after longjmp:
    globval = 95, autoval = 96, regival = 97, volaval = 98, statval = 99

BLZer

用gcc -S 生成汇编程序如下:

    .file    "testjmp.c"     .local    statval.3342     .comm    statval.3342,4,4     .section    .rodata .LC0:     .string    "after longjmp:"     .align 4 .LC1:     .string    "globval = %d, autoval = %d, regival = %d, volaval = %d, statval = %d\n"     .text .globl main     .type    main, @function main:     leal    4(%esp), %ecx     andl    $-16, %esp     pushl    -4(%ecx)     pushl    %ebp     movl    %esp, %ebp     pushl    %ecx     subl    $52, %esp     movl    $1, globval     movl    $2, -8(%ebp)     movl    $3, -24(%ebp)     movl    $4, -12(%ebp)     movl    $5, statval.3342     movl    $jmpbuffer, (%esp)     call    _setjmp     testl    %eax, %eax     je    .L2     movl    $.LC0, (%esp)     call    puts     movl    statval.3342, %eax     movl    -12(%ebp), %edx     movl    globval, %ecx     movl    %eax, 20(%esp)     movl    %edx, 16(%esp)     movl    -24(%ebp), %eax     movl    %eax, 12(%esp)     movl    -8(%ebp), %eax     movl    %eax, 8(%esp)     movl    %ecx, 4(%esp)     movl    $.LC1, (%esp)     call    printf     movl    $0, (%esp)     call    exit .L2:     movl    $95, globval     movl    $96, -8(%ebp)     movl    $97, -24(%ebp)     movl    $98, -12(%ebp)     movl    $99, statval.3342     movl    statval.3342, %eax     movl    -12(%ebp), %edx     movl    %eax, 12(%esp)     movl    %edx, 8(%esp)     movl    -24(%ebp), %eax     movl    %eax, 4(%esp)     movl    -8(%ebp), %eax     movl    %eax, (%esp)     call    f1     movl    $0, (%esp)     call    exit     .size    main, .-main     .section    .rodata .LC2:     .string    "in f1():"     .text     .type    f1, @function f1:     pushl    %ebp     movl    %esp, %ebp     subl    $24, %esp     movl    $.LC2, (%esp)     call    puts     movl    globval, %edx     movl    20(%ebp), %eax     movl    %eax, 20(%esp)     movl    16(%ebp), %eax     movl    %eax, 16(%esp)     movl    12(%ebp), %eax     movl    %eax, 12(%esp)     movl    8(%ebp), %eax     movl    %eax, 8(%esp)     movl    %edx, 4(%esp)     movl    $.LC1, (%esp)     call    printf     call    f2     leave     ret     .size    f1, .-f1     .type    f2, @function f2:     pushl    %ebp     movl    %esp, %ebp     subl    $8, %esp     movl    $1, 4(%esp)     movl    $jmpbuffer, (%esp)     call    longjmp     .size    f2, .-f2     .local    jmpbuffer     .comm    jmpbuffer,156,32     .local    globval     .comm    globval,4,4     .ident    "GCC: (GNU) 4.1.2 20070626 (Red Hat 4.1.2-14)"     .section    .note.GNU-stack,"",@progbits

从这个程序里可以看到,globval 和statval并非是分配在栈上,
照理说longjmp后输出的应该是改变后的值啊?
高手帮忙看下,
谢谢了~~

eelb123

你想说什么。。
不优化是这样啊

BLZer

既然globval和statval没分配在栈上，那么当longjmp回来后，

这两个变量应该不会变成压栈前的值吧？