[BZ,#18508] S390: Fix "backtrace() returns infinitely deep stack frames with makecontext()".
| Message ID | mnj3c8$npj$1@ger.gmane.org |
|---|---|
| State | Dropped |
| Headers |
Received: (qmail 53468 invoked by alias); 8 Jul 2015 12:00:26 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: <libc-alpha.sourceware.org> List-Unsubscribe: <mailto:libc-alpha-unsubscribe-##L=##H@sourceware.org> List-Subscribe: <mailto:libc-alpha-subscribe@sourceware.org> List-Archive: <http://sourceware.org/ml/libc-alpha/> List-Post: <mailto:libc-alpha@sourceware.org> List-Help: <mailto:libc-alpha-help@sourceware.org>, <http://sourceware.org/ml/#faqs> Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 53458 invoked by uid 89); 8 Jul 2015 12:00:25 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.8 required=5.0 tests=AWL, BAYES_00, RCVD_IN_DNSWL_LOW, RP_MATCHES_RCVD, SPF_HELO_PASS, SPF_PASS autolearn=ham version=3.3.2 X-HELO: plane.gmane.org To: libc-alpha@sourceware.org From: Stefan Liebler <stli@linux.vnet.ibm.com> Subject: Re: [PATCH][BZ #18508] S390: Fix "backtrace() returns infinitely deep stack frames with makecontext()". Date: Wed, 08 Jul 2015 14:00:08 +0200 Lines: 117 Message-ID: <mnj3c8$npj$1@ger.gmane.org> References: <ml71gu$et2$1@ger.gmane.org> <557AA306.4090208@redhat.com> <mleq97$5v2$1@ger.gmane.org> <87eglhvsst.fsf@igel.home> <mlm3f3$bbu$1@ger.gmane.org> <559651D0.1030704@redhat.com> <CAMe9rOqs_DPaN=h_dnskMEyvSkG6PrVhr2vXJp7+_sejKenXBg@mail.gmail.com> <CAMe9rOr+tMWUN8ruaLoA9wT_bEcgJx4dfzjXSEVqSwRh-LK7ng@mail.gmail.com> <559C224F.2090600@redhat.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="------------060405050409000107090807" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 In-Reply-To: <559C224F.2090600@redhat.com> |
Commit Message
Stefan Liebler
July 8, 2015, noon UTC
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. Bye Stefan
Comments
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)