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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