Unverified Commit f7b752d2 authored by Daniel Bertalan's avatar Daniel Bertalan
Browse files

[lld-macho] Set the SG_READ_ONLY flag on __DATA_CONST 

This flag instructs dyld to make the segment read-only after fixups have
been performed.

I'm not sure why this flag is needed, as on macOS 13 beta at least,
__DATA_CONST is read-only even without this flag; but ld64 sets it as
well.

Differential Revision: https://reviews.llvm.org/D133010
parent eaede4b5

lld/MachO/OutputSegment.cpp

+7 −0
Original line number Diff line number Diff line
@@ -44,6 +44,12 @@ static uint32_t maxProt(StringRef name) { 
  return initProt(name);

}



static uint32_t flags(StringRef name) {

  // If we ever implement shared cache output support, SG_READ_ONLY should not

  // be used for dylibs that can be placed in it.

  return name == segment_names::dataConst ? SG_READ_ONLY : 0;

}



size_t OutputSegment::numNonHiddenSections() const {

  size_t count = 0;

  for (const OutputSection *osec : sections)
@@ -185,6 +191,7 @@ OutputSegment *macho::getOrCreateOutputSegment(StringRef name) { 
  segRef->name = name;

  segRef->maxProt = maxProt(name);

  segRef->initProt = initProt(name);

  segRef->flags = flags(name);



  outputSegments.push_back(segRef);

  return segRef;

lld/MachO/OutputSegment.h

+1 −0
Original line number Diff line number Diff line
@@ -55,6 +55,7 @@ public: 
  StringRef name;

  uint32_t maxProt = 0;

  uint32_t initProt = 0;

  uint32_t flags = 0;

  uint8_t index;



  llvm::TinyPtrVector<Defined *> segmentStartSymbols;

lld/MachO/Writer.cpp

+1 −0
Original line number Diff line number Diff line
@@ -246,6 +246,7 @@ public: 
    c->vmsize = seg->vmSize;

    c->filesize = seg->fileSize;

    c->nsects = seg->numNonHiddenSections();

    c->flags = seg->flags;



    for (const OutputSection *osec : seg->getSections()) {

      if (osec->isHidden())

lld/test/MachO/builtin-rename.s

+17 −0
Original line number Diff line number Diff line
@@ -53,6 +53,23 @@ 
# YDATA-DAG: __DATA_CONST,__objc_protolist __DATA__objc_protolist

# YDATA-DAG: __DATA_CONST,__nl_symbol_ptr __IMPORT__pointers



## Check that the SG_READ_ONLY flag is set on __DATA_CONST.

# RUN: llvm-otool -v -l %t/ydata | \

# RUN:     FileCheck %s --check-prefix=FLAGS



# FLAGS-LABEL: Load command 2

# FLAGS-NEXT:      cmd LC_SEGMENT_64

# FLAGS-NEXT:  cmdsize

# FLAGS-NEXT:  segname __DATA_CONST

# FLAGS-NEXT:   vmaddr

# FLAGS-NEXT:   vmsize

# FLAGS-NEXT:  fileoff

# FLAGS-NEXT: filesize

# FLAGS-NEXT:  maxprot rw-

# FLAGS-NEXT: initprot rw-

# FLAGS-NEXT:   nsects 13

# FLAGS-NEXT:    flags SG_READ_ONLY



## LLD doesn't support defining symbols in synthetic sections, so we test them

## via this slightly more awkward route.

# RUN: llvm-readobj --section-headers %t/ydata | \

llvm/include/llvm/BinaryFormat/MachO.h

+1 −0
Original line number Diff line number Diff line
@@ -107,6 +107,7 @@ enum : uint32_t { 
  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