On Thu, Apr 20, 2017 at 11:11 AM, evgeny777 <evgeny.levi...@gmail.com> wrote: > Thanks for clarifying it, Dmitry. > > Here is piece of report I get: > > ==18244==ERROR: AddressSanitizer: heap-buffer-overflow on address > 0x60200000001a at pc 0x0000005a9cad bp 0x7ffc10528760 sp 0x7ffc10528740 > WRITE of size 1 at 0x60200000001a thread T0 > #0 0x5a9cac (/home/evgeny/work/linker_scripts/asan/asan+0x5a9cac) > #1 0x7f310488082f (/lib/x86_64-linux-gnu/libc.so.6+0x2082f) > #2 0x419498 (/home/evgeny/work/linker_scripts/asan/asan+0x419498) > > .... > > Below is the piece of disassembly of main : > > ..... > 0x5a9ca8 <+136>: callq 0x56d9d0 ; > ::__asan_report_store1(__sanitizer::uptr) at asan_rtl.cc:136 > 0x5a9cad <+141>: xorl %eax, %eax > ..... > > As you may noticed 0x5a9cac == (0x5a9cad - 1)
I think tsan prints unmodified PC and we should do the same in asan. This also reliefs us from figuring out correct instruction length on ARM/thumb/etc as nobody sees the modified PC. > On Thursday, April 20, 2017 at 12:01:25 PM UTC+3, Dmitry Vyukov wrote: >> >> On Thu, Apr 20, 2017 at 10:44 AM, evgeny777 <evgeny....@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. -- 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.
