On Thu, Apr 20, 2017 at 11:50 AM, Yuri Gribov <tetra2...@gmail.com> wrote: > On Thu, Apr 20, 2017 at 10:20 AM, 'Dmitry Vyukov' via > address-sanitizer <address-sanitizer@googlegroups.com> wrote: >> 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. > > Hm, the unmodified PC will make symbolized stacktraces less readable. > What's the problem with "-1"? Addr2line and other bintools work fine > with it.
I literally mean "print unmodified PC" (as a hex value). I am not proposing to change how symbolization works. >>> 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. > > -- > 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.
