[clang] 7cf4603 - Reland D61689 Change -gz and -Wa,--compress-debug-sections to use gABI compression (SHF_COMPRESSED) with integrated assembler

[Fangrui Song via cfe-commits]

Author: Fangrui Song
Date: 2020-08-03T15:12:01-07:00
New Revision: 7cf4603faee366a6e5860b6fdbedadd91872e231

URL: https://github.com/llvm/llvm-project/commit/7cf4603faee366a6e5860b6fdbedadd91872e231
DIFF: https://github.com/llvm/llvm-project/commit/7cf4603faee366a6e5860b6fdbedadd91872e231.diff

LOG: 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

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/lib/Frontend/CompilerInvocation.cpp
    clang/tools/driver/cc1as_main.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 9274081c4d62..03eca8a26843 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -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
 --------------------

diff  --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 0b5f33541060..8e8bf9d9028e 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -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)

diff  --git a/clang/tools/driver/cc1as_main.cpp b/clang/tools/driver/cc1as_main.cpp
index 77b99b201364..87047be3c2bc 100644
--- a/clang/tools/driver/cc1as_main.cpp
+++ b/clang/tools/driver/cc1as_main.cpp
@@ -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())