VC6/VS2003编译器优化造成的bug

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VC6/VS2003编译器优化造成的bug

2018年02月08日 ⁄ 综合 ⁄ 共 3528字 ⁄ 字号小中大 ⁄ 评论关闭

昨天在CSDN上面看到这样一贴，居然爆料VC6/VS2003有一个严重的bug，于是自己也仔细研究一番：

1、原贴地址：

VC6/VS2003编译器有严重bug !

http://topic.csdn.net/u/20091126/10/81713034-7301-4183-93c0-654d75645582.html

2、出错代码：

// VC6/VC2003 使用/O2编译(默认的release模式), 输出结果有"impossible!!!" #include <stdio.h> int main() { static const int T[1] = {0}; int n = 0; for(int i = 536000000; i < 536000004; ++i) { if(i < 0) { printf("impossible!!!/n"); break; } if(i >= 0 && i < 1) n += T[i]; } printf("end/n"); getchar(); return n; }

3、原因分析

当我在使用IDE环境选择Release生成后，确实发现有上述问题

于是我修改他的代码，狼兄弟建议我先看看此时i的十进制数值与十六进制数值：

#include <stdio.h> int main() { static const int T[1] = {0}; int n = 0; for(int i = 536000000; i < 536000004; ++i) { if(i < 0) { printf("impossible is %d/t%x/n",i,i); break; } if(i >= 0 && i < 1) n += T[i]; } printf("end/n"); return n; }

在命令行编译参数中添加/Fa即可得到汇编代码（当前目录中Hello.asm）：

生成的汇编代码（Release）

TITLE Hello.cpp .386P include listing.inc if @Version gt 510 .model FLAT else _TEXT SEGMENT PARA USE32 PUBLIC 'CODE' _TEXT ENDS _DATA SEGMENT DWORD USE32 PUBLIC 'DATA' _DATA ENDS CONST SEGMENT DWORD USE32 PUBLIC 'CONST' CONST ENDS _BSS SEGMENT DWORD USE32 PUBLIC 'BSS' _BSS ENDS _TLS SEGMENT DWORD USE32 PUBLIC 'TLS' _TLS ENDS ; COMDAT ??_C@_0BF@LPL@impossible?5is?5?$CFd?7?$CFx?6?$AA@ _DATA SEGMENT DWORD USE32 PUBLIC 'DATA' _DATA ENDS ; COMDAT ??_C@_04NBKL@end?6?$AA@ _DATA SEGMENT DWORD USE32 PUBLIC 'DATA' _DATA ENDS ; COMDAT _main _TEXT SEGMENT PARA USE32 PUBLIC 'CODE' _TEXT ENDS FLAT GROUP _DATA, CONST, _BSS ASSUME CS: FLAT, DS: FLAT, SS: FLAT endif CONST SEGMENT _?T@?1??main@@9@4QBHB DD 00H CONST ENDS PUBLIC _main PUBLIC ??_C@_0BF@LPL@impossible?5is?5?$CFd?7?$CFx?6?$AA@ ; `string' PUBLIC ??_C@_04NBKL@end?6?$AA@ ; `string' EXTRN _printf:NEAR ; COMDAT ??_C@_0BF@LPL@impossible?5is?5?$CFd?7?$CFx?6?$AA@ ; File Hello.cpp _DATA SEGMENT ??_C@_0BF@LPL@impossible?5is?5?$CFd?7?$CFx?6?$AA@ DB 'impossible is %d', 09H DB '%x', 0aH, 00H ; `string' _DATA ENDS ; COMDAT ??_C@_04NBKL@end?6?$AA@ _DATA SEGMENT ??_C@_04NBKL@end?6?$AA@ DB 'end', 0aH, 00H ; `string' _DATA ENDS ; COMDAT _main _TEXT SEGMENT _main PROC NEAR ; COMDAT ; File Hello.cpp ; Line 4 push esi ; Line 6 xor esi, esi ; Line 8 mov ecx, 536000000 ; 1ff2b600H mov eax, OFFSET FLAT:_?T@?1??main@@9@4QBHB+2144000000 $L581: ; Line 10 cmp eax, OFFSET FLAT:_?T@?1??main@@9@4QBHB jl SHORT $L595 ; Line 15 cmp eax, OFFSET FLAT:_?T@?1??main@@9@4QBHB+4 jge SHORT $L582 ; Line 16 add esi, DWORD PTR [eax] $L582: add eax, 4 inc ecx cmp eax, OFFSET FLAT:_?T@?1??main@@9@4QBHB+2144000016 jl SHORT $L581 ; Line 19 push OFFSET FLAT:??_C@_04NBKL@end?6?$AA@ ; `string' call _printf add esp, 4 ; Line 20 mov eax, esi pop esi ; Line 21 ret 0 $L595: ; Line 12 push ecx push ecx push OFFSET FLAT:??_C@_0BF@LPL@impossible?5is?5?$CFd?7?$CFx?6?$AA@ ; `string' call _printf add esp, 12 ; 0000000cH ; Line 19 push OFFSET FLAT:??_C@_04NBKL@end?6?$AA@ ; `string' call _printf add esp, 4 ; Line 20 mov eax, esi pop esi ; Line 21 ret 0 _main ENDP _TEXT ENDS END

查看Release生成后在汇编代码：

00401000 push esi 00401001 xor esi,esi 00401003 mov eax,800B5514h 00401008 cmp eax,offset string L"/0" (407D14h) 0040100D jl main+24h (401024h) 0040100F cmp eax,407D18h 00401014 jge main+18h (401018h) 00401016 add esi,dword ptr [eax] 00401018 add eax,4 0040101B cmp eax,800B5524h 00401020 jl main+8 (401008h) 00401022 jmp main+31h (401031h) 00401024 push offset string "impossible!!!/n" (407104h) 00401029 call printf (4011FEh) 0040102E add esp,4 00401031 push offset string "end/n" (4070FCh) 00401036 call printf (4011FEh) 0040103B mov eax,dword ptr [__iob+4 (409044h)] 00401040 add esp,4 00401043 dec eax 00401044 mov dword ptr [__iob+4 (409044h)],eax 00401049 js main+55h (401055h) 0040104B inc dword ptr [__iob (409040h)] 00401051 mov eax,esi 00401053 pop esi 00401054 ret 00401055 push offset __iob (409040h) 0040105A call _filbuf (401066h) 0040105F add esp,4 00401062 mov eax,esi 00401064 pop esi 00401065 ret

可以惊奇的发现i <0会被优化成0x800B5514 <0x00407D14，于是乎让我想起前面编译器优化参数的三个选项，打开IDE的编译选项：

Release