Changes in comdat-selection.s

45b8a741 - [LLD][COFF] When using LLD-as-a-library, always prevent re-entrance on failures

Thu, 12 Nov 2020 13:14:20 +0000

[LLD][COFF] When using LLD-as-a-library, always prevent re-entrance on failuresThis is a follow-up for D70378 (Cover usage of LLD as a library).While debugging an intermittent failure on a bot, I recalled this scenario whichcauses the issue:1.When executing lld/test/ELF/invalid/symtab-sh-info.s L45, we reach lld::elf::Obj-File::ObjFile() which goes straight into its base ELFFileBase(), then ELFFileBase::init().2.At that point fatal() is thrown in lld/ELF/InputFiles.cpp L381, leaving a half-initialized ObjFile instance.3.We then end up in lld::exitLld() and since we are running with LLD_IN_TEST, we hapily restore the control flow to CrashRecoveryContext::RunSafely() then back in lld::safeLldMain().4.Before this patch, we called errorHandler().reset() just after, and this attempted to reset the associated SpecificAlloc>. That tried to free the half-initialized ObjFile instance, and more precisely its ObjFile::dwarf member.Sometimes that worked, sometimes it failed and was catched by theCrashRecoveryContext. This scenario was the reason we callederrorHandler().reset() through a CrashRecoveryContext.But in some rare cases, the above repro somehow corrupted the heap, creating astack overflow. When the CrashRecoveryContext's filter (that is,__except (ExceptionFilter(GetExceptionInformation()))) tried to handle theexception, it crashed again since the stack was exhausted -- and that took thewhole application down. That is the issue seen on the bot. Locally it happensabout 1 times out of 15.Now this situation can happen anywhere in LLD. Since catching stack overflows isnot a reliable scenario ATM when using CrashRecoveryContext, we're nowpreventing further re-entrance when such failures occur, by signalinglld::SafeReturn::canRunAgain=false. When running with LLD_IN_TEST=2 (or above),only one iteration will be executed, instead of two.Differential Revision: https://reviews.llvm.org/D88348 List of files: /llvm-project-15.0.7/lld/test/COFF/comdat-selection.s

04db8cb9 - lld/coff: Simplify error message for comdat selection mismatches

Thu, 14 Feb 2019 03:16:44 +0000

lld/coff: Simplify error message for comdat selection mismatchesTurns out nobody understands what "conflicting comdat type" is supposed tomean, so just emit a regular "duplicate symbol" error and move the comdatselection information into /verbose output.This also fixes a problem where the error output would depend on the order of.obj files passed. Before this patch:- If passed `one_only.obj discard.obj`, lld-link would only err "conflicting comdat type"- If passed `discard.obj one_only.obj`, lld-link would err "conflicting comdat type" and then "duplicate symbol"Now lld-link only errs "duplicate symbol" in both cases.I considered adding a "Detail" parameter to reportDuplicate() that's printed inparens at the end of the "duplicate symbol" diag if present, and then put thecomdat selection mismatch details there, but since users don't know what it'ssupposed to mean decided against it. I also considered special-casing theDetail message for one_only/discard mismatches, which in practice means"function defined as inline in TU 1 but as out-of-line in TU 2", but I wasn'tsure how useful it is so I omitted that too.Differential Revision: https://reviews.llvm.org/D58180llvm-svn: 354006 List of files: /llvm-project-15.0.7/lld/test/COFF/comdat-selection.s

9aa55d3c - lld-link: Allow mixing 'discard' and 'largest' comdat selections

Thu, 31 Jan 2019 16:14:33 +0000

lld-link: Allow mixing 'discard' and 'largest' comdat selectionscl.exe and clang-cl.exe put vftables in a 'discard' comdat when building withRTTI disabled (/GR-) but in a 'largest' comdat when building with RTTI enabled.To be able to link /GR- code with /GR code, lld-link needs to accept comdatsthat have this type of comdat selection conflict.For example, static libraries in the Visual Studio standard library are builtwith /GR, and without this it's impossible to build client code with /GR- andstill link to the standard library.link.exe also accepts merging 'discard' with 'largest', and it accepts merging'largest' with any other selection type. lld-link is still a bit stricter sinceit only allows merging 'largest' with 'discard' for symmetry.Differential Revision: https://reviews.llvm.org/D57515llvm-svn: 352765 List of files: /llvm-project-15.0.7/lld/test/COFF/comdat-selection.s

48dc110e - lld/coff: Implement some support for the comdat selection field

Wed, 30 Jan 2019 02:17:27 +0000

lld/coff: Implement some support for the comdat selection fieldLLD used to handle comdats as if the selection field was always set toIMAGE_COMDAT_SELECT_ANY. This means for obj files produced by `cl /Gy`, LLDwould never report a duplicate symbol error.This change:- adds validation for the Selection field (should make no difference in practice for compiler-generated obj inputs)- rejects comdats that have different Selection fields in different obj files (likewise). This is a bit more strict but also more self-consistent thank link.exe (see comment in code)- implements handling for all the selection kindsIn practice, compilers only generate comdats withIMAGE_COMDAT_SELECT_NODUPLICATES (LLD now produces duplicate symbol errors forthese), IMAGE_COMDAT_SELECT_ANY (no behavior change), andIMAGE_COMDAT_SELECT_LARGEST (for RTTI data; here LLD should no longer createbroken executables when linking some TUs with RTTI enabled and some with itdisabled – but see below).The implementation of `IMAGE_COMDAT_SELECT_LARGEST` is incomplete: If oneSELECT_LARGEST comdat replaces an earlier one, the comdat symbol is replacedcorrectly, but the old section stays loaded and if /opt:ref is disabled (via/opt:noref or /debug) it's still written to the output. That's not ideal, butbetter than the current treatment of just picking any one of those comdats. Ihope to fix this better later.Fixes most of PR40094.Differential Revision: https://reviews.llvm.org/D57324llvm-svn: 352590 List of files: /llvm-project-15.0.7/lld/test/COFF/comdat-selection.s