使用-O3时确定段错误的原因？

问题描述 投票：0回答：1

当使用 

-O3
和 GCC 4.8/4.9/5.1 编译程序时，我无法确定段错误的原因。对于 GCC 4.9.x，我在 Cygwin、Debian 8 (x64) 和 Fedora 21 (x64) 上看到过它。其他人在 GCC 4.8 和 5.1 上经历过。

该程序在 

-O2
下运行良好，在其他版本的 GCC 下运行良好，在其他编译器（如 MSVC、ICC 和 Clang）下运行良好。

下面是 GDB 下的崩溃，但我没有发现任何异常。来自

misc.cpp:26
的源代码如下，但它是一个简单的异或：

((word64*)buf)[i] ^= ((word64*)mask)[i];

相关代码在转换之前检查 64 位字对齐情况。从-O3下的反汇编，我知道它与

vmovdqa
指令有关：
(gdb) disass 0x0000000000539fc3 ... 0x0000000000539fbc <+220>: vxorps 0x0(%r13,%r10,1),%ymm0,%ymm0 => 0x0000000000539fc3 <+227>: vmovdqa %ymm0,0x0(%r13,%r10,1) 0x0000000000539fca <+234>: add $0x20,%r10 

看来 GCC 在
-O3

处使用 SSE 向量，而不是在 

-O2
处使用它们。 （感谢 Alejandro 的建议）。
我会天真地问：

vmovdqa

的对齐要求是否大于64位字？是的，为什么 GCC 在字不是 128 位对齐的情况下选择它？
这里出现段错误的原因是什么？我该如何进一步排除故障？

另请参阅
错误 66852 - 在 64 位对齐数组上发出的 vmovdqa 指令会导致段错误

。这是针对此问题提交的，因此目前尚未得到证实。

$ gdb ./cryptest.exe GNU gdb (Debian 7.7.1+dfsg-5) 7.7.1 ... (gdb) r v ... Testing MessageDigest algorithm SHA-3-224. ..... Program received signal SIGSEGV, Segmentation fault. 0x0000000000539fc3 in CryptoPP::xorbuf (buf=0x98549a "efghijde", mask=mask@entry=0x7fffffffbfeb "efghijdefghijkefghijklfghijklmghijklmnhijklmnoijklmnopjklmnopqklmnopqrlmnopqrsmnopqrstnopqrstu", 'a' <repeats 106 times>..., count=count@entry=0x5e) at misc.cpp:26 26 ((word64*)buf)[i] ^= ((word64*)mask)[i];
(gdb) where #0 0x0000000000539fc3 in CryptoPP::xorbuf (buf=0x98549a "efghijde", mask=mask@entry=0x7fffffffbfeb "efghijdefghijkefghijklfghijklmghijklmnhijklmnoijklmnopjklmnopqklmnopqrlmnopqrsmnopqrstnopqrstu", 'a' <repeats 106 times>..., count=count@entry=0x5e) at misc.cpp:26 #1 0x0000000000561eb0 in CryptoPP::SHA3::Update (this=0x985480, input=0x7fffffffbfeb "efghijdefghijkefghijklfghijklmghijklmnhijklmnoijklmnopjklmnopqklmnopqrlmnopqrsmnopqrstnopqrstu", 'a' <repeats 106 times>..., length=0x5e) at sha3.cpp:264 #2 0x00000000005bac1a in CryptoPP::HashVerificationFilter::NextPutMultiple ( this=0x7fffffffd390, inString=0x7fffffffbfeb "efghijdefghijkefghijklfghijklmghijklmnhijklmnoijklmnopjklmnopqklmnopqrlmnopqrsmnopqrstnopqrstu", 'a' <repeats 106 times>..., length=0x5e) at filters.cpp:786 #3 0x00000000005bd8a2 in NextPutMaybeModifiable (modifiable=<optimized out>, length=0x5e, inString=0x7fffffffbfeb "efghijdefghijkefghijklfghijklmghijklmnhijklmnoijklmnopjklmnopqklmnopqrlmnopqrsmnopqrstnopqrstu", 'a' <repeats 106 times>..., this=0x7fffffffd390) at filters.h:200 #4 CryptoPP::FilterWithBufferedInput::PutMaybeModifiable ( this=0x7fffffffd390, inString=0x7fffffffbfeb "efghijdefghijkefghijklfghijklmghijklmnhijklmnoijklmnopjklmnopqklmnopqrlmnopqrsmnopqrstnopqrstu", 'a' <repeats 106 times>..., length=<optimized out>, messageEnd=0x0, blocking=<optimized out>, ...
-O3

反汇编并注册值。
(gdb) disass 0x0000000000539fc3 Dump of assembler code for function CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long): 0x0000000000539ee0 <+0>: lea 0x8(%rsp),%r10 0x0000000000539ee5 <+5>: and $0xffffffffffffffe0,%rsp 0x0000000000539ee9 <+9>: mov %rdx,%rax 0x0000000000539eec <+12>: pushq -0x8(%r10) 0x0000000000539ef0 <+16>: push %rbp 0x0000000000539ef1 <+17>: shr $0x3,%rax 0x0000000000539ef5 <+21>: mov %rsp,%rbp 0x0000000000539ef8 <+24>: push %r15 0x0000000000539efa <+26>: push %r14 0x0000000000539efc <+28>: push %r13 0x0000000000539efe <+30>: push %r12 0x0000000000539f00 <+32>: push %r10 0x0000000000539f02 <+34>: push %rbx 0x0000000000539f03 <+35>: je 0x53a00a <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+298> 0x0000000000539f09 <+41>: lea 0x20(%rdi),%rcx 0x0000000000539f0d <+45>: cmp %rcx,%rsi 0x0000000000539f10 <+48>: lea 0x20(%rsi),%rcx 0x0000000000539f14 <+52>: setae %r8b 0x0000000000539f18 <+56>: cmp %rcx,%rdi 0x0000000000539f1b <+59>: setae %cl 0x0000000000539f1e <+62>: or %cl,%r8b 0x0000000000539f21 <+65>: je 0x53a300 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+1056> 0x0000000000539f27 <+71>: cmp $0x8,%rax 0x0000000000539f2b <+75>: jbe 0x53a300 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+1056> 0x0000000000539f31 <+81>: mov %rdi,%rcx 0x0000000000539f34 <+84>: and $0x1f,%ecx 0x0000000000539f37 <+87>: shr $0x3,%rcx 0x0000000000539f3b <+91>: neg %rcx 0x0000000000539f3e <+94>: and $0x3,%ecx 0x0000000000539f41 <+97>: cmp %rax,%rcx 0x0000000000539f44 <+100>: cmova %rax,%rcx 0x0000000000539f48 <+104>: xor %r8d,%r8d 0x0000000000539f4b <+107>: test %rcx,%rcx 0x0000000000539f4e <+110>: je 0x539f80 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+160> 0x0000000000539f50 <+112>: mov (%rsi),%r8 0x0000000000539f53 <+115>: xor %r8,(%rdi) 0x0000000000539f56 <+118>: cmp $0x1,%rcx 0x0000000000539f5a <+122>: je 0x53a371 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+1169> 0x0000000000539f60 <+128>: mov 0x8(%rsi),%r8 0x0000000000539f64 <+132>: xor %r8,0x8(%rdi) 0x0000000000539f68 <+136>: cmp $0x3,%rcx 0x0000000000539f6c <+140>: jne 0x53a366 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+1158> 0x0000000000539f72 <+146>: mov 0x10(%rsi),%r8 0x0000000000539f76 <+150>: xor %r8,0x10(%rdi) 0x0000000000539f7a <+154>: mov $0x3,%r8d 0x0000000000539f80 <+160>: mov %rax,%r11 0x0000000000539f83 <+163>: xor %r10d,%r10d 0x0000000000539f86 <+166>: sub %rcx,%r11 0x0000000000539f89 <+169>: shl $0x3,%rcx 0x0000000000539f8d <+173>: xor %ebx,%ebx 0x0000000000539f8f <+175>: lea -0x4(%r11),%r9 0x0000000000539f93 <+179>: lea (%rdi,%rcx,1),%r13 0x0000000000539f97 <+183>: shr $0x2,%r9 0x0000000000539f9b <+187>: add %rsi,%rcx 0x0000000000539f9e <+190>: add $0x1,%r9 0x0000000000539fa2 <+194>: lea 0x0(,%r9,4),%r12 0x0000000000539faa <+202>: add $0x1,%rbx 0x0000000000539fae <+206>: vmovdqu (%rcx,%r10,1),%xmm0 0x0000000000539fb4 <+212>: vinsertf128 $0x1,0x10(%rcx,%r10,1),%ymm0,%ymm0 0x0000000000539fbc <+220>: vxorps 0x0(%r13,%r10,1),%ymm0,%ymm0 => 0x0000000000539fc3 <+227>: vmovdqa %ymm0,0x0(%r13,%r10,1) 0x0000000000539fca <+234>: add $0x20,%r10 0x0000000000539fce <+238>: cmp %r9,%rbx 0x0000000000539fd1 <+241>: jb 0x539faa <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+202> 0x0000000000539fd3 <+243>: lea (%r8,%r12,1),%rcx 0x0000000000539fd7 <+247>: cmp %r12,%r11 0x0000000000539fda <+250>: je 0x53a006 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+294> 0x0000000000539fdc <+252>: mov (%rsi,%rcx,8),%r8 0x0000000000539fe0 <+256>: xor %r8,(%rdi,%rcx,8) 0x0000000000539fe4 <+260>: lea 0x1(%rcx),%r8 0x0000000000539fe8 <+264>: cmp %r8,%rax 0x0000000000539feb <+267>: jbe 0x53a006 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+294> 0x0000000000539fed <+269>: add $0x2,%rcx 0x0000000000539ff1 <+273>: mov (%rsi,%r8,8),%r9 0x0000000000539ff5 <+277>: xor %r9,(%rdi,%r8,8) 0x0000000000539ff9 <+281>: cmp %rcx,%rax 0x0000000000539ffc <+284>: jbe 0x53a006 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+294> 0x0000000000539ffe <+286>: mov (%rsi,%rcx,8),%r8 0x000000000053a002 <+290>: xor %r8,(%rdi,%rcx,8) 0x000000000053a006 <+294>: shl $0x3,%rax 

并且：

(gdb) info r ymm0 r13 r10 ymm0 {v8_float = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, v4_double = {0x8000000000000000, 0x8000000000000000, 0x8000000000000000, 0x8000000000000000}, v32_int8 = {0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x68, 0x69}, v16_int16 = {0x6766, 0x6968, 0x6b6a, 0x6665, 0x6867, 0x6a69, 0x6c6b, 0x6766, 0x6968, 0x6b6a, 0x6d6c, 0x6867, 0x6a69, 0x6c6b, 0x6e6d, 0x6968}, v8_int32 = {0x69686766, 0x66656b6a, 0x6a696867, 0x67666c6b, 0x6b6a6968, 0x68676d6c, 0x6c6b6a69, 0x69686e6d}, v4_int64 = { 0x66656b6a69686766, 0x67666c6b6a696867, 0x68676d6c6b6a6968, 0x69686e6d6c6b6a69}, v2_int128 = {0x67666c6b6a69686766656b6a69686766, 0x69686e6d6c6b6a6968676d6c6b6a6968}} r13 0x9854a2 0x9854a2 r10 0x0 0x0
当使用
-O2

和相关行上的断点进行编译时，这是反汇编。 

((word64*)buf)[i] ^= ((word64*)mask)[i];
移至第31行：
Breakpoint 1, CryptoPP::xorbuf (buf=0x985488 "", mask=mask@entry=0x7fffffffc01d "The quick brown fox", 'a' <repeats 181 times>..., count=count@entry=0x13) at misc.cpp:31 31 ((word64*)buf)[i] ^= ((word64*)mask)[i]; (gdb) disass Dump of assembler code for function CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long): 0x0000000000532150 <+0>: mov %rdx,%rcx 0x0000000000532153 <+3>: shr $0x3,%rcx 0x0000000000532157 <+7>: je 0x532170 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+32> 0x0000000000532159 <+9>: xor %eax,%eax => 0x000000000053215b <+11>: mov (%rsi,%rax,8),%r8 0x000000000053215f <+15>: xor %r8,(%rdi,%rax,8) 0x0000000000532163 <+19>: add $0x1,%rax 0x0000000000532167 <+23>: cmp %rcx,%rax 0x000000000053216a <+26>: jne 0x53215b <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+11> 0x000000000053216c <+28>: shl $0x3,%rcx 0x0000000000532170 <+32>: sub %rcx,%rdx 0x0000000000532173 <+35>: je 0x5321d0 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+128> 0x0000000000532175 <+37>: mov %rdx,%r8 0x0000000000532178 <+40>: add %rcx,%rdi 0x000000000053217b <+43>: add %rcx,%rsi 0x000000000053217e <+46>: shr $0x2,%r8 0x0000000000532182 <+50>: je 0x5321a8 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+88> 0x0000000000532184 <+52>: xor %eax,%eax 0x0000000000532186 <+54>: nopw %cs:0x0(%rax,%rax,1) 0x0000000000532190 <+64>: mov (%rsi,%rax,4),%ecx 0x0000000000532193 <+67>: xor %ecx,(%rdi,%rax,4) 0x0000000000532196 <+70>: add $0x1,%rax 0x000000000053219a <+74>: cmp %r8,%rax 0x000000000053219d <+77>: jne 0x532190 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+64> 0x000000000053219f <+79>: shl $0x2,%r8 0x00000000005321a3 <+83>: sub %r8,%rdx 0x00000000005321a6 <+86>: je 0x5321d8 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+136> 0x00000000005321a8 <+88>: lea (%rdi,%r8,1),%rcx 0x00000000005321ac <+92>: xor %eax,%eax 0x00000000005321ae <+94>: lea (%rsi,%r8,1),%rdi 0x00000000005321b2 <+98>: nopw 0x0(%rax,%rax,1) 0x00000000005321b8 <+104>: movzbl (%rdi,%rax,1),%esi 0x00000000005321bc <+108>: xor %sil,(%rcx,%rax,1) 0x00000000005321c0 <+112>: add $0x1,%rax 0x00000000005321c4 <+116>: cmp %rdx,%rax 0x00000000005321c7 <+119>: jb 0x5321b8 <CryptoPP::xorbuf(unsigned char*, unsigned char const*, unsigned long)+104> 0x00000000005321c9 <+121>: retq 0x00000000005321ca <+122>: nopw 0x0(%rax,%rax,1) 0x00000000005321d0 <+128>: retq 0x00000000005321d1 <+129>: nopl 0x0(%rax) 0x00000000005321d8 <+136>: retq End of assembler dump.
从
misc.cpp

开始，第26行是

((word64*)buf)[i] ^= ((word64*)mask)[i];
。
void xorbuf(byte *buf, const byte *mask, size_t count) { size_t i; if (IsAligned<word32>(buf) && IsAligned<word32>(mask)) { if (!CRYPTOPP_BOOL_SLOW_WORD64 && IsAligned<word64>(buf) && IsAligned<word64>(mask)) { for (i=0; i<count/8; i++) ((word64*)buf)[i] ^= ((word64*)mask)[i]; count -= 8*i; if (!count) return; buf += 8*i; mask += 8*i; } for (i=0; i<count/4; i++) ((word32*)buf)[i] ^= ((word32*)mask)[i]; count -= 4*i; if (!count) return; buf += 4*i; mask += 4*i; } for (i=0; i<count; i++) buf[i] ^= mask[i]; } 




    
    c++
    
    gdb
    
    sse
    
    gcc4.9
    
    
1个回答

    

      
      
      

        

          

            

              
7
投票

              

            

          

        

        
g++ -Wall -Wextra -O3 -g
 进行编译；您想要启用警告，因为其中一些警告可能仅在使用 
 -O3
 启用的 GCC 通道中生成；您希望启用调试信息 (
-g
) 来使用 
gdb
，但请注意，通过强大的优化，调试信息并不总是可靠的。
您可能会遇到一些“指针别名”问题。也许使用（或删除） 
restrict
 关键字。
一定要避免
未定义的行为
。您可以对 
-fsanitize=
 编译器（最好是版本 5）使用 -fsanitize=address 选项（特别是 
-fsanitize=undefined
 和 
g++
....） 还可以使用 
valgrind
。
顺便说一句，您可以使用像 -fdump-tree-all 这样的转储选项（警告，它们会生成数百个文件！）来了解更多 
g++
 的内部行为；您甚至可以使用 
MELT
 自定义您的 GCC 编译器（过时且原始 URL 已抢注）。
此外，如果查看生成的汇编程序，请使用 g++ -Wall -S -O3 -fverbose-asm 进行编译，因为 
-fverbose-asm
 要求 GCC 发出一些汇编程序注释“解释”（不多，但有一点点）编译后的代码。
    





      

      
    

  

  

    
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