[PATCH] D118494: [lldb] Observe SG_READ_ONLY flag in MachO binaries

[Dave Lee via Phabricator via llvm-commits]

kastiglione created this revision.
kastiglione added reviewers: aprantl, augusto2112.
kastiglione requested review of this revision.
Herald added projects: LLDB, LLVM.
Herald added subscribers: llvm-commits, lldb-commits.

Change `Section::GetPermissions()` to indicate non-writability when the Mach-O
segment has the `SG_READ_ONLY` flag.

MachO has a segment flag named `SG_READ_ONLY` which indicates that the segment
is semantically read-only, even if its permissions are marked writable.
Segments such as `__DATA_CONST` contain data that is semantically "const", but
needs to be writable for dyld to perform fixups (bindings or rebases).

The header documentation for `SG_READ_ONLY` states:

> This segment is made read-only after fixups.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D118494

Files:
  lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
  llvm/include/llvm/BinaryFormat/MachO.h


Index: llvm/include/llvm/BinaryFormat/MachO.h
===================================================================
--- llvm/include/llvm/BinaryFormat/MachO.h
+++ llvm/include/llvm/BinaryFormat/MachO.h
@@ -106,6 +106,7 @@
   SG_FVMLIB = 0x2u,
   SG_NORELOC = 0x4u,
   SG_PROTECTED_VERSION_1 = 0x8u,
+  SG_READ_ONLY = 0x10u,
 
   // Constant masks for the "flags" field in llvm::MachO::section and
   // llvm::MachO::section_64
Index: lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
===================================================================
--- lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
+++ lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
@@ -1433,7 +1433,7 @@
   uint32_t result = 0;
   if (seg_cmd.initprot & VM_PROT_READ)
     result |= ePermissionsReadable;
-  if (seg_cmd.initprot & VM_PROT_WRITE)
+  if ((seg_cmd.initprot & VM_PROT_WRITE) && !(seg_cmd.flags & SG_READ_ONLY))
     result |= ePermissionsWritable;
   if (seg_cmd.initprot & VM_PROT_EXECUTE)
     result |= ePermissionsExecutable;


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