Hi, all I think this issue causes the gdb crash on XP. You can see the thread: http://sourceware.org/ml/gdb/2011-10/msg00056.html
My many friends and I can reproduce this crash issue, but no problem on Win7. On Thu, Oct 20, 2011 at 5:05 AM, Bob Breuer <breu...@mc.net> wrote: > Kai Tietz wrote: >> 2011/10/18 Bob Breuer <breu...@mc.net>: >>> Kai Tietz wrote: >>>> 2011/10/17 Bob Breuer <breu...@mc.net>: >>>>> Richard Henderson wrote: >>>>>> On 10/17/2011 07:09 AM, Bob Breuer wrote: >>>>>>> Google finds a mention of longjmp failing with -fomit-frame-pointer: >>>>>>> http://lua-users.org/lists/lua-l/2005-02/msg00158.html >>>>>>> >>>>>>> Looks like gcc 4.6 turns on -fomit-frame-pointer by default. >>>>>> Hmm. This is the first I've heard of a longjmp implementation >>>>>> failing without a frame pointer. Presumably this is with the >>>>>> mingw i.e. msvc libc? >>>>> Yeah, mingw from www.mingw.org which I believe uses msvcrt.dll, package >>>>> gcc-core-4.6.1-2-mingw32-bin. >>>>> >>>>>> This is something that could be worked around in gcc, I suppose. >>>>>> We recognize longjmp for some things, we could force the use of >>>>>> a frame pointer for msvc targets too. >>>>>> >>>>>> For now it might be best to simply force -fno-omit-frame-pointer >>>>>> for mingw host in the configure script. >>>>> Here's a testcase that crashes on the longjmp: >>>>> >>>>> #include <stdio.h> >>>>> #include <setjmp.h> >>>>> >>>>> jmp_buf env; >>>>> >>>>> int test(void) >>>>> { >>>>> int i; >>>>> >>>>> asm("xor %%ebp,%%ebp" ::: "ebp"); >>>>> >>>>> i = setjmp(env); >>>>> printf("i = %d\n", i); >>>>> >>>>> if (i == 0) >>>>> longjmp(env, 2); >>>>> >>>>> return i; >>>>> } >>>>> >>>>> int main(void) >>>>> { >>>>> return test(); >>>>> } >>>>> >>>>> Remove the asm statement to make it not crash. Obviously with >>>>> omit-frame-pointer, gcc can shove anything into ebp. >>>>> >>>>> Bob >>>> This crash isn'r related to ebp existing, or not. The issue is the >>>> hidden argument of setjmp, which is missing. If you can try the >>>> following at top of file after include section. >>>> >>>> #define setjmp(BUF) _setjmpex((BUF), NULL) >>>> int __cdecl __attribute__ ((__nothrow__,__returns_twice__)) >>>> _setjmp3(jmp_buf _Buf, void *_Ctx); >>>> ... >>> Did you mean _setjmp3 instead of _setjmpex? With _setjmp3, it works >>> without the asm, but still crashes if I zero out ebp before the setjmp. >>> Aren't the function arguments on the stack anyway? >> >> Yes, I mean _setjmp3 (pasto from headers and missed the second line >> prototyping _setjmp3). >> I repeat myself here. setjmp() has an hidden arguement, which is >> passed on x86 on stack. By not passing this required argument, setjmp >> will take a random-value from stack. In your case 'i'. btw if you >> would pre-initialize 'i' with zero, I would assume you won't see a >> crash, but anyway this is just by chance. >> For this I suggest to use here _setjmp3 instead, as here >> second-argument is documented as being present. >> >> Btw I tested your code with i686-pc-mingw32 version 4.6.x and 4.7.x >> gcc version. With my suggested pattern, I don't see a crash for your >> provide test-code with, or without zero-ing ebp. > > > We probably have a difference in build or run environment. I've > double-checked with another machine and can get the same crash in > longjmp when running the test executable on both WinXP and Win2k, but > not on Win7. So it looks like Microsoft may have changed this "feature" > somewhere between WinXP and Win7. > > The msvcrt implementation of longjmp (or at least the one I'm looking > at) does a ebp based access using the saved value of ebp. Here's the > relevant disassembly of longjmp: > > 0x7801e6f3 in longjmpex () from C:\WINNT\system32\msvcrt.dll > (gdb) disas > Dump of assembler code for function longjmpex: > 0x7801e6ef <+0>: mov 0x4(%esp),%ebx > => 0x7801e6f3 <+4>: mov (%ebx),%ebp > ... > 0x7801e73d <+78>: call 0x7800bd5e <abnormal_termination+56> > ... > 0x7800bd5e <+56>: push %ebx > 0x7800bd5f <+57>: push %ecx > 0x7800bd60 <+58>: mov $0x7803dc64,%ebx > => 0x7800bd65 <+63>: mov 0x8(%ebp),%ecx > > It crashes on the access of 0x8(%ebp). Those are the only 2 places > where this version of longjmp touches ebp. Is it possible to force a > stackframe by just adding a suitable attribute to either the setjmp > function prototype, or the function which calls setjmp? > > Bob > -- Best Regards, xunxun
