My involvement with LLVM 18

LLVM 18 will soon be relased. This post provides a summary of my contributions in this release cycle to record my learning progress.

• LLVM binary utility maintenance, e.g.
  • adopted llvm-readobj style ObjectFile specific dumpers
  • [llvm-objdump][X86] Add @plt symbols for .plt.got
  • [llvm-readobj] Print <null> for relocation target with an empty name
  • Support --decompress/-z (#82594)
• sanitizer maintenance, e.g.
  • [asan] Enable StackSafetyAnalysis by default
  • asan_static x86-64: Support 64-bit ASAN_SHADOW_OFFSET_CONST (#75748)
  • [asan] Report executable/DSO name for report_globals=2 and odr-violation checking (#71879)
  • changed lsan to work with high-entropy ASLR for x86-64 Linux
  • removed crypt and crypt_r interceptors to work with glibc
  • implemented interceptors for glibc 2.38 __isoc23_strtol and __isoc23_scanf family functions
  • tsan: Respect !nosanitize metadata and remove gcov special case
  • [dfsan] Wrap glibc 2.38 __isoc23_* functions (#79958)
  • -fsanitize=alignment: check memcpy/memmove arguments (#67766)
• gcov maintenance
  • Ignore blocks from another file to fix a crash
• LTO maintenance
  • Improve diagnostics handling when parsing module-level inline assembly (#75726)
• MC maintenance
  • [MC,AArch64] Suppress local symbol to STT_SECTION conversion for GOT relocations
  • MC Make .pseudo_probe created sections deterministic after D91878
  • Change .reloc to register used symbols
  • Change SHF_LINK_ORDER and section group parsing order to match GNU assembler
• AArch32
  • [ARM,ELF] Fix access to dso_preemptable __stack_chk_guard with static relocation model (#70014)
• AArch64
  • Suppress local symbol to STT_SECTION conversion for GOT relocations
  • Restrict MOVZ/MOVK to non-PIC large code model (#70178)
  • clang: Define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 for AArch64 (#74954)
• MIPS
  • Use generic isBlockOnlyReachableByFallthrough (#80799)
• RISC-V
  • Clean up code after improved assembler support for linker relaxation
  • Support R_RISCV_SET_ULEB128/R_RISCV_SUB_ULEB128 for .uleb128 directives
  • Parse SHF_LINK_ORDER argument before section group name (#77407)
  • R_RISCV_CALL/R_RISCV_CALL_PLT assembler and assembly parser cleanup
  • Force relocations if initial MCSubtargetInfo contains FeatureRelax (#77436)
• x86
  • Support inline assembly constraint "Ws"
  • Change displacement overflow when parsing assembly code (#75747)
  • Fix MSVC-style inline assembly call fptr and jmp fptr (#73207)
  • In 32-bit mode, fix FastISel -fno-pic for intrinsics to emit R_386_PC32 instead of R_386_PLT32 (#51078)
  • clang: Support arch=x86-64{,-v2,-v3,-v4} for target_clones attribute
  • clang: __builtin_cpu_supports: support x86-64{,-v2,-v3,-v4}
• libunwind
  • Bump to CXX_STANDARD 17 (#75986)

lld

See lld 18 ELF changes

MC

• Removed many obsoleted workarounds from the integrated assembler
• Fixed placement of function entry comments
• Re-architectured a substantial part of the integrated assembler that is used by RISC-V linker relaxation, fixing some longstanding bugs. See The dark side of RISC-V linker relaxation for detail.

Clang

Driver maintenance

• [Driver] -###: exit with code 1 if hasErrorOccurred
• Report errors for target-specific options on unsupported targets
• Remove RequiresPIE and msan's NeedPIE setting (#77689)
• Add -fandroid-pad-segment/-fno-android-pad-segment (#77244)
• Support -mtls-dialect=desc

Others:

• Function multi-versioning: don't set comdat for internal linkage resolvers

Code review

Reviewed many patches, including ADT/Support, binary utilities, MC, lld (sometimes non-ELF ports even if my primary expertise is in ELF), clangDriver, LTO, sanitizers, LoongArch, RISC-V, x86-64 medium/large code models, etc.

TODO is:pr is:closed sort:updated-desc review-requested:@me lists pull requests that requested a review from me, but it's unclear how to list pull requests that I've made a comment.

Link: My involvement with LLVM 17