[PATCH] D61689: Change -gz and -Wa,--compress-debug-sections to use gABI compression (SHF_COMPRESSED)

[Fangrui Song via Phabricator via cfe-commits]

MaskRay created this revision.
MaskRay added reviewers: compnerd, rsmith, echristo.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

Since July 15, 2015 (binutils-gdb commit
19a7fe52ae3d0971e67a134bcb1648899e21ae1c, included in 2.26), gas
--compress-debug-sections=zlib (gcc -gz) means zlib-gabi:
SHF_COMPRESSED.  Before that it meant zlib-gnu (.zdebug).

clang's -gz was introduced in rC306115 <https://reviews.llvm.org/rC306115> (Jun 2017) to indicate zlib-gnu. It
is 2019 now and it is not unreasonable to assume users of the new
feature to have new linkers (ld.bfd/gold >= 2.26, lld >= rLLD273661 <https://reviews.llvm.org/rLLD273661>).

Change clang's default accordingly to improve standard conformance.
zlib-gnu becomes out of fashion and gets poorer toolchain support.
Its mangled names confuse tools and are more likely to cause problems,
e.g.

lld up to 8.0.0 (and probably some older ld.bfd/gold) don't handle -r
linking of .rela.zdebug_* correctly: .rela.zdebug_* output sections are
created without compression. Consumers which assume these sections are
zlib-gnu may have parsing errors.


Repository:
  rC Clang

https://reviews.llvm.org/D61689

Files:
  lib/Frontend/CompilerInvocation.cpp
  tools/driver/cc1as_main.cpp


Index: tools/driver/cc1as_main.cpp
===================================================================
--- tools/driver/cc1as_main.cpp
+++ tools/driver/cc1as_main.cpp
@@ -221,8 +221,7 @@
   if (const Arg *A = Args.getLastArg(OPT_compress_debug_sections,
                                      OPT_compress_debug_sections_EQ)) {
     if (A->getOption().getID() == OPT_compress_debug_sections) {
-      // TODO: be more clever about the compression type auto-detection
-      Opts.CompressDebugSections = llvm::DebugCompressionType::GNU;
+      Opts.CompressDebugSections = llvm::DebugCompressionType::Z;
     } else {
       Opts.CompressDebugSections =
           llvm::StringSwitch<llvm::DebugCompressionType>(A->getValue())
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -1052,8 +1052,7 @@
   if (const Arg *A = Args.getLastArg(OPT_compress_debug_sections,
                                      OPT_compress_debug_sections_EQ)) {
     if (A->getOption().getID() == OPT_compress_debug_sections) {
-      // TODO: be more clever about the compression type auto-detection
-      Opts.setCompressDebugSections(llvm::DebugCompressionType::GNU);
+      Opts.setCompressDebugSections(llvm::DebugCompressionType::Z);
     } else {
       auto DCT = llvm::StringSwitch<llvm::DebugCompressionType>(A->getValue())
                      .Case("none", llvm::DebugCompressionType::None)


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