[lld-macho] Fix LOH parsing segfault

`advanceSubsection()` didn't account for the possibility that a section
could have no subsections.

Reviewed By: #lld-macho, thakis, BertalanD

Differential Revision: https://reviews.llvm.org/D130288

diff --git a/lld/MachO/InputFiles.cpp b/lld/MachO/InputFiles.cpp
index a2c27f1..d39fa5f 100644 (file)
--- a/lld/MachO/InputFiles.cpp
+++ b/lld/MachO/InputFiles.cpp
@@ -560,7 +560,7 @@ void ObjFile::parseOptimizationHints(ArrayRef<uint8_t> data) {
     if (section == sections.end())
       return;
     ++subsection;
-    if (subsection == (*section)->subsections.end()) {
+    while (subsection == (*section)->subsections.end()) {
       ++section;
       if (section == sections.end())
         return;
@@ -582,6 +582,7 @@ void ObjFile::parseOptimizationHints(ArrayRef<uint8_t> data) {
         if (section == sections.end())
           break;
         updateAddr();
+        assert(hintStart->offset0 >= subsectionBase);
       }
     }
 

diff --git a/lld/test/MachO/loh-parsing.s b/lld/test/MachO/loh-parsing.s
new file mode 100644 (file)
index 0000000..aad1af3
--- /dev/null
+++ b/lld/test/MachO/loh-parsing.s
@@ -0,0 +1,24 @@
+# REQUIRES: aarch64
+
+# RUN: llvm-mc -filetype=obj -triple=arm64-apple-darwin %s -o %t.o
+# RUN: %lld -arch arm64 -dylib %t.o -o /dev/null
+
+## Check that we parse the LOH & match it to its referent sections correctly,
+## even when there are other subsections that don't get parsed as regular
+## sections. (We would previously segfault.)
+## __debug_info is one such section that gets special-case handling.
+
+.text
+_foo:
+
+.section __DWARF,__debug_info,regular,debug
+
+## __StaticInit occurs after __debug_info in the input object file, so the
+## LOH-matching code will have to "walk" past __debug_info while searching for
+## __StaticInit. Thus this verifies that we can skip past __debug_info
+## correctly.
+.section __TEXT,__StaticInit
+L1:  adrp  x1, _foo@PAGE
+L2:  ldr   x1, [x1, _foo@PAGEOFF]
+
+.loh AdrpLdr L1, L2