[PATCH] D30291: Handle section header flags redefinitions similar to GAS

[Christof Douma via Phabricator via llvm-commits]

christof created this revision.

A .section directive defining an already existing section has now the following behavior:

- target specific flags (that is OS or PROC specific) are added to the existing section
- Any other flag is ignored and a warning is emitted

This makes the integrated assembler behave like GNU as  version 2.27.


Repository:
  rL LLVM

https://reviews.llvm.org/D30291

Files:
  lib/MC/MCParser/ELFAsmParser.cpp
  test/MC/ELF/section-override-flags.s


Index: test/MC/ELF/section-override-flags.s
===================================================================
--- /dev/null
+++ test/MC/ELF/section-override-flags.s
@@ -0,0 +1,36 @@
+// RUN: llvm-mc -filetype=obj -triple arm-pc-linux-gnu %s -o %t 2>&1 | FileCheck -check-prefix=DIAG %s
+// RUN: llvm-readobj -s %t | FileCheck %s
+
+// REQUIRES: arm-registered-target
+
+// Test we handle overriding OS and PROC specific flags on the builtin .text section
+.section .text,"0x200006",%progbits
+.section .text,"0x40000006",%progbits
+
+// CHECK:      Section {
+// CHECK:        Name: .text
+// CHECK-NEXT:   Type: SHT_PROGBITS (0x1)
+// CHECK-NEXT:   Flags [ (0x40200006)
+// CHECK-NEXT:     SHF_ALLOC (0x2)
+// CHECK-NEXT:     SHF_EXECINSTR (0x4)
+// CHECK-NEXT:   ]
+
+//Attempt to override flags that are not target specific should be ignored
+.section foo,"ax",%progbits
+.section foo,"0x7",%progbits
+.section foo,"0x10000007",%progbits
+
+// DIAG: warning: ignoring override of non-target sepecific section flags
+// DIAG: warning: ignoring override of non-target sepecific section flags
+
+// CHECK:      Section {
+// CHECK:        Name: foo
+// CHECK-NEXT:   Type: SHT_PROGBITS (0x1)
+// CHECK-NEXT:   Flags [ (0x10000006)
+// CHECK-NEXT:     SHF_ALLOC (0x2)
+// CHECK-NEXT:     SHF_EXECINSTR (0x4)
+// CHECK-NEXT:   ]
+
+
+// We want to see this warning the exact number times specified
+// DIAG-NOT: warning: ignoring override of non-target sepecific section flags
Index: lib/MC/MCParser/ELFAsmParser.cpp
===================================================================
--- lib/MC/MCParser/ELFAsmParser.cpp
+++ lib/MC/MCParser/ELFAsmParser.cpp
@@ -594,8 +594,20 @@
       }
   }
 
-  MCSection *ELFSection = getContext().getELFSection(
+  MCSectionELF *ELFSection = getContext().getELFSection(
       SectionName, Type, Flags, Size, GroupName, UniqueID, Associated);
+  // Sections are not identified by flags. Check if there is a mismatch in the
+  // flags requested and the flags in the section returned. If the mismatch is
+  // in OS or CPU specific flags, just add them. For any other mismatch warn
+  // the user that we are ignoring the new flags.
+  const unsigned overrideMask = (ELF::SHF_MASKOS | ELF::SHF_MASKPROC);
+  unsigned curFlags = ELFSection->getFlags();
+  curFlags |= Flags & overrideMask;
+  Flags |= curFlags & overrideMask;
+  ELFSection->setFlags(curFlags);
+  if (curFlags != Flags)
+    Warning(loc, "ignoring override of non-target sepecific section flags");
+
   getStreamer().SwitchSection(ELFSection, Subsection);
 
   if (getContext().getGenDwarfForAssembly()) {


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