On Thu, Apr 20, 2017 at 10:44 AM, evgeny777 <evgeny.levi...@gmail.com> wrote: > I noticed that GetPreviousInstructionPc() function returns 'pc - 1' for both > arm32 and arm64. > This causes odd addresses to appear in stack traces, which is nonsense, as > both arm32/64 instructions > have 4 byte size and alignment. > > The x86 and x86_64 cases are even more confusing, because instruction length > is not constant. What exactly this 'pc - 1' is expected to return? > > But even if one is able to get previous instruction address correctly he may > still get confusing results. In case some instruction triggers > hardware exception, its address will go to ASAN stack trace (via > SlowUnwindStackWithContext). Returning address of previous instruction > in such case can be extremely confusing. > > Is there any point in using this function?
Hi, Yes, there is a very bold point in using this function. Typically top frame PC is obtained with __builtin_return_address, which means that it points to the next instruction after the call. And we need to obtain debug info associated with the call instruction. To achieve that we subtract 1 from PC. All symbolization code that we've seen is fine with PC pointing into a middle of an instruction. Now, if we print pc-1 in reports (do we?), then it's a bug. We need to print unaltered PC in reports. Re hardware exceptions. This needs to be fixed. A trivial change would be to add 1 to PCs pointing to faulting instruction. Then GetPreviousInstructionPc will offset this and we get correct debug info. However, then we will print incorrect PC in report. So a proper fix would be to augment all stack traces with a flag saying if top PC needs to be adjusted during symbolization or not. -- You received this message because you are subscribed to the Google Groups "address-sanitizer" group. To unsubscribe from this group and stop receiving emails from it, send an email to address-sanitizer+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
