On Thu, Apr 20, 2017 at 10:53 AM, 'Dmitry Vyukov' via address-sanitizer <address-sanitizer@googlegroups.com> wrote: > 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.
My understanding is that symbolization code symbolizes "pc-1" as well. If we keep symbolization code unchanged and only change printed hex value, this will probly cause offline symbolizer to behave differently from internal symbolizer. Actually the situation is even more interesting: on ARM we do pc & (~1) (not pc-1) to cancel out Thumb bit. >>>> 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. -- 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.
