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Reland D61689 Change -gz and -Wa,--compress-debug-sections to use gABI compression (SHF_COMPRESSED) with integrated assembler 

This fixes an inconsistency: clang -c -gz -fno-integrated-as means SHF_COMPRESSED
while clang -c -gz -fintegrated-as means zlib-gnu.

---

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 GCC/binutils used zlib-gnu (.zdebug).

clang's -gz was introduced in rC306115 (Jun 2017) to indicate zlib-gnu. It
is 2020 now and it is not unreasonable to assume users of the new
feature to have new linkers (ld.bfd/gold >= 2.26, lld >= 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.

Reviewed By: compnerd

Differential Revision: https://reviews.llvm.org/D61689
This commit is contained in:
Fangrui Song 2020-08-03 15:11:28 -07:00 committed by Fangrui Song
parent 089adc339e
commit 7cf4603fae
3 changed files with 6 additions and 5 deletions
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5
clang/docs/ReleaseNotes.rst
View File

@ -100,7 +100,10 @@ future versions of Clang.
Modified Compiler Flags
-----------------------
- ...
- On ELF, ``-gz`` now defaults to ``-gz=zlib`` with the integrated assembler.
It produces ``SHF_COMPRESSED`` style compression of debug information. GNU
binutils 2.26 or newer, or lld is required to link produced object files. Use
``-gz=zlib-gnu`` to get the old behavior.
New Pragmas in Clang
--------------------

3
clang/lib/Frontend/CompilerInvocation.cpp
View File

@ -1155,8 +1155,7 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
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)

3
clang/tools/driver/cc1as_main.cpp
View File

@ -224,8 +224,7 @@ bool AssemblerInvocation::CreateFromArgs(AssemblerInvocation &Opts,
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())