[PATCH] D60965: [llvm-mc] - Properly set the the address align field of the compressed sections.

[George Rimar via Phabricator via llvm-commits]

grimar created this revision.
grimar added reviewers: dblaikie, echristo, ruiu.
Herald added subscribers: MaskRay, arichardson, emaste.
Herald added a reviewer: espindola.

About the compressed sections spec says:
(https://docs.oracle.com/cd/E37838_01/html/E36783/section_compression.html)
sh_addralign fields of the section header for a compressed section
reflect the requirements of the compressed section.

Currently, llvm-mc always puts uncompressed section alignment to sh_addralign.
It is not correct. zlib styled section contains an Elfxx_Chdr header,
so we should either use 4 or 8 values depending on the target
(Uncompressed section alignment is stored in ch_addralign field of the compression header).

GNU assembler version 2.31.1 also has this issue,
but in 2.32.51 it was already fixed. This is how it was found
during debugging of the https://bugs.llvm.org/show_bug.cgi?id=40482
actually.


https://reviews.llvm.org/D60965

Files:
  lib/MC/ELFObjectWriter.cpp
  test/MC/ELF/compression.s


Index: test/MC/ELF/compression.s
===================================================================
--- test/MC/ELF/compression.s
+++ test/MC/ELF/compression.s
@@ -10,9 +10,11 @@
 // RUN: llvm-mc -filetype=obj -compress-debug-sections=zlib -triple x86_64-pc-linux-gnu < %s -o %t
 // RUN: llvm-objdump -s %t | FileCheck --check-prefix=CHECK-ZLIB-STYLE %s
 // RUN: llvm-dwarfdump -debug-str %t | FileCheck --check-prefix=STR %s
-// RUN: llvm-mc -filetype=obj -compress-debug-sections=zlib -triple i386-pc-linux-gnu < %s \
-// RUN:     | llvm-readobj -symbols - | FileCheck --check-prefix=386-SYMBOLS-ZLIB %s
-// RUN: llvm-readobj -sections %t | FileCheck --check-prefix=ZLIB-STYLE-FLAGS %s
+// RUN: llvm-readobj -sections %t | FileCheck --check-prefixes=ZLIB-STYLE-FLAGS,ZLIB-STYLE-FLAGS64 %s
+
+// RUN: llvm-mc -filetype=obj -compress-debug-sections=zlib -triple i386-pc-linux-gnu < %s -o %t
+// RUN: llvm-readobj -symbols -sections %t \
+// RUN:   | FileCheck --check-prefixes=386-SYMBOLS-ZLIB,ZLIB-STYLE-FLAGS,ZLIB-STYLE-FLAGS32 %s
 
 // Don't compress small sections, such as this simple debug_abbrev example
 // CHECK-GNU-STYLE: Contents of section .debug_abbrev:
@@ -60,6 +62,16 @@
 // ZLIB-STYLE-FLAGS-NEXT:   Type: SHT_PROGBITS
 // ZLIB-STYLE-FLAGS-NEXT:   Flags [
 // ZLIB-STYLE-FLAGS-NEXT:     SHF_COMPRESSED
+// ZLIB-STYLE-FLAGS-NEXT:     SHF_MERGE
+// ZLIB-STYLE-FLAGS-NEXT:     SHF_STRINGS
+// ZLIB-STYLE-FLAGS-NEXT:   ]
+// ZLIB-STYLE-FLAGS-NEXT:   Address:
+// ZLIB-STYLE-FLAGS-NEXT:   Offset:
+// ZLIB-STYLE-FLAGS-NEXT:   Size:
+// ZLIB-STYLE-FLAGS-NEXT:   Link:
+// ZLIB-STYLE-FLAGS-NEXT:   Info:
+// ZLIB-STYLE-FLAGS32-NEXT: AddressAlignment: 4
+// ZLIB-STYLE-FLAGS64-NEXT: AddressAlignment: 8
 
 // 386-SYMBOLS-ZLIB: Name: .Linfo_string0
 // 386-SYMBOLS-ZLIB-NOT: }
Index: lib/MC/ELFObjectWriter.cpp
===================================================================
--- lib/MC/ELFObjectWriter.cpp
+++ lib/MC/ELFObjectWriter.cpp
@@ -886,12 +886,16 @@
     return;
   }
 
-  if (ZlibStyle)
+  if (ZlibStyle) {
     // Set the compressed flag. That is zlib style.
     Section.setFlags(Section.getFlags() | ELF::SHF_COMPRESSED);
-  else
+    // Alignment field should reflect the requirements of
+    // the compressed section header.
+    Section.setAlignment(is64Bit() ? 8 : 4);
+  } else {
     // Add "z" prefix to section name. This is zlib-gnu style.
     MC.renameELFSection(&Section, (".z" + SectionName.drop_front(1)).str());
+  }
   W.OS << CompressedContents;
 }
 


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