[BOLT] Error out on SHF_COMPRESSED debug sections (#185662)

Some binaries are built using `-gz=zstd`, but when using
`--update-debug-sections` on said binaries BOLT crashes.

This patch fixes this issue by recognising compressed debug sections in
binaries via their flag `SHF_COMPRESSED` and appropriately erroring out.

Legacy GNU-style compression is not handled.

bolt/include/bolt/Rewrite/RewriteInstance.h

@@ -409,6 +409,9 @@ public:
   /// Return true if the section holds debug information.
   static bool isDebugSection(StringRef SectionName);
 
+  /// Return true if a debug section is compressed (by SHF_COMPRESSED flag).
+  static bool isCompressedDebugSection(const object::SectionRef &Section);
+
   /// Adds Debug section to overwrite.
   static void addToDebugSectionsToOverwrite(const char *Section) {
     DebugSectionsToOverwrite.emplace_back(Section);

bolt/lib/Rewrite/RewriteInstance.cpp

@@ -2196,6 +2196,19 @@ Error RewriteInstance::readSpecialSections() {
     check_error(SectionNameOrErr.takeError(), "cannot get section name");
     StringRef SectionName = *SectionNameOrErr;
 
+    // Detect a debug section and check if it's compressed.
+    // Compressed debug sections currently aren't supported.
+    if (isDebugSection(SectionName)) {
+      HasDebugInfo = true;
+      if (opts::UpdateDebugSections && isCompressedDebugSection(Section)) {
+        return createStringError(errc::not_supported,
+                                 Twine("compressed debug section '") +
+                                     SectionName +
+                                     "' detected. --update-debug-sections "
+                                     "requires uncompressed debug info");
+      }
+    }
+
     if (Error E = Section.getContents().takeError())
       return E;
     BC->registerSection(Section);
@@ -2204,8 +2217,6 @@ Error RewriteInstance::readSpecialSections() {
                << Twine::utohexstr(Section.getAddress()) << ":0x"
                << Twine::utohexstr(Section.getAddress() + Section.getSize())
                << "\n");
-    if (isDebugSection(SectionName))
-      HasDebugInfo = true;
   }
 
   // Set IsRelro section attribute based on PT_GNU_RELRO segment.
@@ -6491,3 +6502,7 @@ bool RewriteInstance::isDebugSection(StringRef SectionName) {
 
   return false;
 }
+
+bool RewriteInstance::isCompressedDebugSection(const SectionRef &Section) {
+  return (ELFSectionRef(Section).getFlags() & ELF::SHF_COMPRESSED) != 0;
+}

bolt/test/AArch64/Inputs/compressed-debug-sections.yaml

@@ -0,0 +1,27 @@
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_AARCH64
+  Entry:           0x48000
+ProgramHeaders:
+  - Type:            PT_LOAD
+    Flags:           [ PF_X, PF_R ]
+    FirstSec:        .text
+    LastSec:         .text
+    VAddr:           0x48000
+    Align:           0x4000
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x48000
+    AddressAlign:    0x4
+    Content:         030F0B0700000000030F0B0700000000C0035FD6FFFFFF97000080D2A80B8052010000D4
+  - Name:            .debug_info
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_COMPRESSED ]
+    AddressAlign:    0x1
+    Content:         0200000000000000DD33310000000000010000000000000028B52FFDA000001000CC6207
+...

bolt/test/AArch64/compressed-debug-sections.test

@@ -0,0 +1,6 @@
+// Checks that BOLT correctly errors out on compressed debug sections.
+//
+// RUN: yaml2obj %p/Inputs/compressed-debug-sections.yaml -o %t.exe
+// RUN: not llvm-bolt %t.exe -o %t.bolt --update-debug-sections 2>&1 | FileCheck %s
+//
+// CHECK: compressed debug section '.debug_info' detected. --update-debug-sections requires uncompressed debug info