| Message ID | mnj3c8$npj$1@ger.gmane.org |
|---|---|
| State | New |
| Headers | show |
On 07/08/2015 08:00 AM, Stefan Liebler wrote: > On 07/07/2015 09:02 PM, Carlos O'Donell wrote: >> On 07/07/2015 01:47 PM, H.J. Lu wrote: >>> I opened: >>> https://sourceware.org/bugzilla/show_bug.cgi?id=18635 >> >> Stefan, >> >> Please fix this promptly as glibc 2.22 will be released >> shortly and the test results should be clean. If we can't >> fix it promptly, then we should revert the test changes. >> >> Cheers, >> Carlos. >> > Hi, > > the testcase seems to be okay, but there is a bug in i686 backtrace handling if the context was set via makecontext. > If we revert the test changes, the test case will pass, but the bug is only hidden. If that's the case then please file a bug on sourceware for this particular failure, mark the test as XFAIL for i686 and use a comment to reference the bug when you mark it XFAIL. Cheers, Carlos.
On Wed, Jul 8, 2015 at 5:00 AM, Stefan Liebler <stli@linux.vnet.ibm.com> wrote: > On 07/07/2015 09:02 PM, Carlos O'Donell wrote: >> >> On 07/07/2015 01:47 PM, H.J. Lu wrote: >>> >>> I opened: >>> https://sourceware.org/bugzilla/show_bug.cgi?id=18635 >> >> >> Stefan, >> >> Please fix this promptly as glibc 2.22 will be released >> shortly and the test results should be clean. If we can't >> fix it promptly, then we should revert the test changes. >> >> Cheers, >> Carlos. >> > Hi, > > the testcase seems to be okay, but there is a bug in i686 backtrace handling > if the context was set via makecontext. > If we revert the test changes, the test case will pass, but the bug is only > hidden. > > If you call backtrace() function in such a context, you'll get a > segmentation fault, too. backtrace () also uses _Unwind_Backtrace. > > The "exitcode"-block within __makecontext in > sysdeps/unix/sysv/linux/i386/makecontext.S is surrounded by cfi_endproc and > cfi_startproc. > The start addresses of these cfi's seems okay, but the end addresses are > strange - see readelf/objdump output below. > > readelf --debug-dump=frames libc.so: > 000043dc 00000014 000043e0 FDE cie=00000000 pc=0003f610..0e44f810 > Augmentation data: 41 0e 04 10 00 00 00 f8 > > 000043f4 00000010 000043f8 FDE cie=00000000 pc=0003f67e..0003f67e > Augmentation data: 00 00 00 0c 44 00 00 d8 43 ec ff a6 00 00 00 0 > > objdump -d libc.so: > /* ENTRY(__makecontext) */ > 0003f610 <makecontext>: > 3f610: 8b 44 24 04 mov 0x4(%esp),%eax > ... > /* cfi_endproc in makecontext.S. */ > /* L(exitcode): */ > 3f65b: 8d 24 9c lea (%esp,%ebx,4),%esp > 3f65e: e8 00 00 00 00 call 3f663 <makecontext+0x53> > 3f663: 5b pop %ebx > 3f664: 81 c3 91 39 16 00 add $0x163991,%ebx > 3f66a: 83 3c 24 00 cmpl $0x0,(%esp) > 3f66e: 74 08 je 3f678 <makecontext+0x68> > 3f670: e8 2b ff ff ff call 3f5a0 <setcontext> > 3f675: 89 04 24 mov %eax,(%esp) > 3f678: e8 13 01 ff ff call 2f790 <exit> > 3f67d: f4 hlt > /* cfi_startproc in makecontext.S. */ > /* END(__makecontext) */ > 3f67e: 90 nop > 3f67f: 90 nop > > > For a quick test, I extracted the exitcode-block to a new function with > ENTRY/END-macros and undefined cfi_start/end_proc, like it is done in > s390-makecontext_ret - see attached patch. Afterwards _Unwind_backtrace does > not segfault anymore. > > Please test/comment. It works. Thanks.
On 07/08/2015 10:43 AM, Carlos O'Donell wrote: > On 07/08/2015 08:00 AM, Stefan Liebler wrote: >> On 07/07/2015 09:02 PM, Carlos O'Donell wrote: >>> On 07/07/2015 01:47 PM, H.J. Lu wrote: >>>> I opened: >>>> https://sourceware.org/bugzilla/show_bug.cgi?id=18635 >>> >>> Stefan, >>> >>> Please fix this promptly as glibc 2.22 will be released >>> shortly and the test results should be clean. If we can't >>> fix it promptly, then we should revert the test changes. >>> >>> Cheers, >>> Carlos. >>> >> Hi, >> >> the testcase seems to be okay, but there is a bug in i686 backtrace handling if the context was set via makecontext. >> If we revert the test changes, the test case will pass, but the bug is only hidden. > > If that's the case then please file a bug on sourceware for > this particular failure, mark the test as XFAIL for i686 and > use a comment to reference the bug when you mark it XFAIL. Bug 18635 was already filed by H.J, so use that. c.
On 07/08/2015 10:44 AM, H.J. Lu wrote: >> For a quick test, I extracted the exitcode-block to a new function with >> ENTRY/END-macros and undefined cfi_start/end_proc, like it is done in >> s390-makecontext_ret - see attached patch. Afterwards _Unwind_backtrace does >> not segfault anymore. >> >> Please test/comment. > > It works. But we don't really know why... c.
On Wed, Jul 8, 2015 at 7:47 AM, Carlos O'Donell <carlos@redhat.com> wrote: > On 07/08/2015 10:44 AM, H.J. Lu wrote: >>> For a quick test, I extracted the exitcode-block to a new function with >>> ENTRY/END-macros and undefined cfi_start/end_proc, like it is done in >>> s390-makecontext_ret - see attached patch. Afterwards _Unwind_backtrace does >>> not segfault anymore. >>> >>> Please test/comment. >> >> It works. > > But we don't really know why... > The hand-written frame info in i386/makecontext.S is wrong as shown in https://sourceware.org/bugzilla/show_bug.cgi?id=18635 Program received signal SIGSEGV, Segmentation fault. uw_frame_state_for (context=context@entry=0x8050120 <st1+15968>, fs=fs@entry=0x80501a0 <st1+16096>) at /export/gnu/import/git/sources/gcc/libgcc/unwind-dw2.c:1249 1249 return MD_FALLBACK_FRAME_STATE_FOR (context, fs); (gdb) bt #0 uw_frame_state_for (context=context@entry=0x8050120 <st1+15968>, fs=fs@entry=0x80501a0 <st1+16096>) at /export/gnu/import/git/sources/gcc/libgcc/unwind-dw2.c:1249 #1 0xf7e102a8 in _Unwind_Backtrace (trace=0x8049420 <backtrace_helper>, trace_argument=0x8050298 <st1+16344>) at /export/gnu/import/git/sources/gcc/libgcc/unwind.inc:290 #2 0x080494a6 in cf (i=-78) at tst-makecontext.c:72 #3 0xf7e55d1b in makecontext () at ../sysdeps/unix/sysv/linux/i386/makecontext.S:87 #4 0xffffffb2 in ?? () <<<<<<<< Bogus return address #5 0x00000000 in ?? () (gdb)
diff --git a/sysdeps/unix/sysv/linux/i386/makecontext.S b/sysdeps/unix/sysv/linux/i386/makecontext.S index 8364fb9..f88abf9 100644 --- a/sysdeps/unix/sysv/linux/i386/makecontext.S +++ b/sysdeps/unix/sysv/linux/i386/makecontext.S @@ -85,6 +85,7 @@ ENTRY(__makecontext) #endif /* 'makecontext' returns no value. */ ret +END(__makecontext) /* This is the helper code which gets called if a function which is registered with 'makecontext' returns. In this case we @@ -92,7 +93,11 @@ ENTRY(__makecontext) the context 'makecontext' manipulated at the time of the 'makecontext' call. If the pointer is NULL the process must terminate. */ - cfi_endproc +#undef cfi_startproc +#define cfi_startproc +#undef cfi_endproc +#define cfi_endproc +ENTRY(__makecontext_ret) L(exitcode): /* This removes the parameters passed to the function given to 'makecontext' from the stack. EBX contains the number of @@ -116,7 +121,6 @@ L(exitcode): /* The 'exit' call should never return. In case it does cause the process to terminate. */ hlt - cfi_startproc -END(__makecontext) +END(__makecontext_ret) weak_alias (__makecontext, makecontext)