[lld][mach-o] Avoid segfaulting when handling an empty section list.
Summary:
The following patch avoids segfaulting if the section list is empty when writing a mach-o MH_OBJECT. I ran into this case from a more complicated example trying to dead_strip while using '-r' in lld.
I'm not sure if having empty sections is a legal mach-o, but it does seem that other llvm-binutils tools can ingest such a boring object with out issue. Would it be better to emit an error, emit a warning, or do nothing? It seems that adding a warning diagnostic might be helpful to users, as I did not expect to have a section-less object when the linker was done.
Reviewers: kledzik, ruiu
Subscribers: llvm-commits, jrm
Tags: #lld, #llvm
Differential Revision: https://reviews.llvm.org/D67735
git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@372995 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp b/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp
index da27c7c..ab7ea7e 100644
--- a/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp
+++ b/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp
@@ -626,17 +626,19 @@
+ _file.sections.size() * sizeof(typename T::section);
uint8_t *next = lc + seg->cmdsize;
memset(seg->segname, 0, 16);
+ seg->flags = 0;
seg->vmaddr = 0;
- seg->vmsize = _file.sections.back().address
- + _file.sections.back().content.size();
seg->fileoff = _endOfLoadCommands;
- seg->filesize = _sectInfo[&_file.sections.back()].fileOffset +
- _file.sections.back().content.size() -
- _sectInfo[&_file.sections.front()].fileOffset;
seg->maxprot = VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE;
seg->initprot = VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE;
seg->nsects = _file.sections.size();
- seg->flags = 0;
+ if (seg->nsects) {
+ seg->vmsize = _file.sections.back().address
+ + _file.sections.back().content.size();
+ seg->filesize = _sectInfo[&_file.sections.back()].fileOffset +
+ _file.sections.back().content.size() -
+ _sectInfo[&_file.sections.front()].fileOffset;
+ }
if (_swap)
swapStruct(*seg);
typename T::section *sout = reinterpret_cast<typename T::section*>
diff --git a/test/mach-o/empty-sections.yaml b/test/mach-o/empty-sections.yaml
new file mode 100644
index 0000000..ca6b150
--- /dev/null
+++ b/test/mach-o/empty-sections.yaml
@@ -0,0 +1,9 @@
+# RUN: ld64.lld -arch x86_64 -r %s -o %t
+#
+# Test that writing empty mach-o sections does not segfault the linker.
+#
+
+--- !mach-o
+arch: x86_64
+file-type: MH_OBJECT
+...
