I hacked the UBSan runtime locally to use the fast unwinder. I thought this
"worked", but it seems to only print one frame. This explains why:
67 void BufferedStackTrace::FastUnwindStack(uptr pc, uptr bp, uptr stack_top,
68 uptr stack_bottom, u32 max_depth)
{
69 const uptr kPageSize = GetPageSizeCached();
70 CHECK_GE(max_depth, 2);
71 trace_buffer[0] = pc;
72 size = 1;
73 if (stack_top < 4096) return; // Sanity check for stack top.
There is a comment by Alexey Samsonov giving a warning about this:
34 // We can only use slow unwind, as we don't have any information about
stack
35 // top/bottom.
36 // FIXME: It's better to respect "fast_unwind_on_fatal" runtime flag and
37 // fetch stack top/bottom information if we have it (e.g. if we're
running
38 // under ASan).
39 if (StackTrace::WillUseFastUnwind(false))
40 return;
So, in the absence of stack top/bottom info, we'd need to add support for the
slow unwinder.
vedant
> On Apr 14, 2017, at 10:19 AM, Kuba Mracek <mra...@apple.com> wrote:
>
> What exactly is wrong with the fast unwinder? It's used in ASan and TSan and
> besides not knowing about inlined frames, it works great. But we're almost
> always dealing with code that has frame pointers (and the sanitizer runtimes
> themselves are built with frame pointers).
>
> Kuba
>
>> On 13 Apr 2017, at 19:18, Vedant Kumar via cfe-commits
>> <cfe-commits@lists.llvm.org> wrote:
>>
>> Does anyone know what it would take to get the slow unwinder to work on
>> Darwin?
>>
>> thanks,
>> vedant
>>
>>> On Apr 13, 2017, at 6:59 PM, Vedant Kumar via cfe-commits
>>> <cfe-commits@lists.llvm.org> wrote:
>>>
>>> Author: vedantk
>>> Date: Thu Apr 13 20:59:44 2017
>>> New Revision: 300295
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=300295&view=rev
>>> Log:
>>> [docs] UBSan: Mention that print_stacktrace=1 is unsupported on Darwin
>>>
>>> Printing out stack traces along with UBSan diagnostics is unsupported on
>>> Darwin. That's because it isn't possible to use the fast unwinder or the
>>> slow unwinder.
>>>
>>> Apparently, it's inappropriate to use the fast unwinder for UBSan
>>> issues. I'm not exactly sure why (see the comment in ubsan_diag.cc).
>>> Forcing use of the fast unwinder produces decent results, AFAICT.
>>>
>>> Darwin also does not appear to have a slow unwinder suitable for use
>>> with the sanitizers. Apparently that's because of PR20800 [1][2]. But
>>> that bug has been fixed. I'm not sure if there is anything preventing
>>> use of the slow unwinder now.
>>>
>>> Currently, passing UBSAN_OPTIONS=print_stacktrace=1 does nothing on
>>> Darwin. This isn't good, but it might be a while before we can fix the
>>> situation, so we should at least document it.
>>>
>>> [1] https://github.com/google/sanitizers/issues/137
>>> "We can't use the slow unwinder on OSX now, because Clang produces
>>> incorrect unwind info for the ASan runtime functions on OSX
>>> (http://llvm.org/PR20800)."
>>>
>>> [2] https://bugs.llvm.org/show_bug.cgi?id=20800
>>> Bug 20800 - Invalid compact unwind info generated for a function without
>>> frame pointers on OSX
>>>
>>> Modified:
>>> cfe/trunk/docs/UndefinedBehaviorSanitizer.rst
>>>
>>> Modified: cfe/trunk/docs/UndefinedBehaviorSanitizer.rst
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/UndefinedBehaviorSanitizer.rst?rev=300295&r1=300294&r2=300295&view=diff
>>> ==============================================================================
>>> --- cfe/trunk/docs/UndefinedBehaviorSanitizer.rst (original)
>>> +++ cfe/trunk/docs/UndefinedBehaviorSanitizer.rst Thu Apr 13 20:59:44 2017
>>> @@ -157,6 +157,8 @@ will need to:
>>> ``UBSAN_OPTIONS=print_stacktrace=1``.
>>> #. Make sure ``llvm-symbolizer`` binary is in ``PATH``.
>>>
>>> +Stacktrace printing for UBSan issues is currently not supported on Darwin.
>>> +
>>> Issue Suppression
>>> =================
>>>
>>>
>>>
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>>> cfe-commits mailing list
>>> cfe-commits@lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
>>
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