[lld] [lld-macho] Fix code section ordering in output binary (PR #134010)
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Tue Apr 1 17:38:33 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-lld
Author: None (alx32)
<details>
<summary>Changes</summary>
In `OutputSegment.cpp`, we need to ensure a specific order for certain sections. The current sorting logic incorrectly prioritizes code sections over explicitly defined section orders. This is problematic because the `__objc_stubs` section is both a code section *and* has a specific ordering requirement. The current logic would incorrectly prioritize its code section status, causing it to be sorted *before* the `__stubs` section. This incorrect ordering breaks the branch extension algorithm, ultimately leading to linker failures due to relocation errors.
We also modify the `lld/test/MachO/arm64-objc-stubs.s` test to ensure correct section ordering.
---
Full diff: https://github.com/llvm/llvm-project/pull/134010.diff
2 Files Affected:
- (modified) lld/MachO/OutputSegment.cpp (+22-10)
- (modified) lld/test/MachO/arm64-objc-stubs.s (+18-10)
``````````diff
diff --git a/lld/MachO/OutputSegment.cpp b/lld/MachO/OutputSegment.cpp
index c320af3fb3177..185444673ae47 100644
--- a/lld/MachO/OutputSegment.cpp
+++ b/lld/MachO/OutputSegment.cpp
@@ -103,20 +103,32 @@ static int sectionOrder(OutputSection *osec) {
// be the section that determines whether we need thunks or not.
if (osec->name == section_names::text)
return -6;
+
+ // Prioritize specific section ordering based on our knowledge. This ensures
+ // that certain sections are placed in a particular order, even if they
+ // are also categorized as code sections. This explicit ordering takes
+ // precedence over the general code section ordering.
+ int knownPriority =
+ StringSwitch<int>(osec->name)
+ .Case(section_names::stubs, -4)
+ .Case(section_names::stubHelper, -3)
+ .Case(section_names::objcStubs, -2)
+ .Case(section_names::initOffsets, -1)
+ .Case(section_names::unwindInfo,
+ std::numeric_limits<int>::max() - 1)
+ .Case(section_names::ehFrame, std::numeric_limits<int>::max())
+ .Default(0);
+
+ if (knownPriority != 0)
+ return knownPriority;
+
// Ensure all code sections are contiguous with `__text` for thunk
// calculations.
- if (sections::isCodeSection(osec->name, segment_names::text, osec->flags) &&
- osec->name != section_names::stubHelper) {
+ if (sections::isCodeSection(osec->name, segment_names::text, osec->flags)) {
return -5;
}
- return StringSwitch<int>(osec->name)
- .Case(section_names::stubs, -4)
- .Case(section_names::stubHelper, -3)
- .Case(section_names::objcStubs, -2)
- .Case(section_names::initOffsets, -1)
- .Case(section_names::unwindInfo, std::numeric_limits<int>::max() - 1)
- .Case(section_names::ehFrame, std::numeric_limits<int>::max())
- .Default(osec->inputOrder);
+
+ return osec->inputOrder;
} else if (segname == segment_names::data ||
segname == segment_names::dataConst) {
// For each thread spawned, dyld will initialize its TLVs by copying the
diff --git a/lld/test/MachO/arm64-objc-stubs.s b/lld/test/MachO/arm64-objc-stubs.s
index 1b8ebff924300..da25b1292faa6 100644
--- a/lld/test/MachO/arm64-objc-stubs.s
+++ b/lld/test/MachO/arm64-objc-stubs.s
@@ -1,22 +1,23 @@
# REQUIRES: aarch64
# RUN: llvm-mc -filetype=obj -triple=arm64-apple-darwin %s -o %t.o
-# RUN: %lld -arch arm64 -lSystem -o %t.out %t.o
+# RUN: %lld -arch arm64 -lSystem -o %t.out %t.o -U _external_func
# RUN: llvm-otool -vs __TEXT __objc_stubs %t.out | FileCheck %s
-# RUN: %lld -arch arm64 -lSystem -o %t.out %t.o -dead_strip
+# RUN: %lld -arch arm64 -lSystem -o %t.out %t.o -dead_strip -U _external_func
# RUN: llvm-otool -vs __TEXT __objc_stubs %t.out | FileCheck %s
-# RUN: %lld -arch arm64 -lSystem -o %t.out %t.o -objc_stubs_fast
+# RUN: %lld -arch arm64 -lSystem -o %t.out %t.o -objc_stubs_fast -U _external_func
# RUN: llvm-otool -vs __TEXT __objc_stubs %t.out | FileCheck %s
# RUN: llvm-otool -l %t.out | FileCheck %s --check-prefix=FASTALIGN
-# RUN: %lld -arch arm64 -lSystem -o %t.out %t.o -objc_stubs_small
+# RUN: %lld -arch arm64 -lSystem -o %t.out %t.o -objc_stubs_small -U _external_func
# RUN: llvm-otool -vs __TEXT __objc_stubs %t.out | FileCheck %s --check-prefix=SMALL
# RUN: llvm-otool -l %t.out | FileCheck %s --check-prefix=SMALLALIGN
+# RUN: llvm-objdump --section-headers %t.out | FileCheck %s --check-prefix=SECTIONS
# CHECK: Contents of (__TEXT,__objc_stubs) section
# CHECK-NEXT: _objc_msgSend$foo:
# CHECK-NEXT: adrp x1, 8 ; 0x100008000
-# CHECK-NEXT: ldr x1, [x1, #0x10]
+# CHECK-NEXT: ldr x1, [x1, #0x18]
# CHECK-NEXT: adrp x16, 4 ; 0x100004000
# CHECK-NEXT: ldr x16, [x16]
# CHECK-NEXT: br x16
@@ -26,7 +27,7 @@
# CHECK-NEXT: _objc_msgSend$length:
# CHECK-NEXT: adrp x1, 8 ; 0x100008000
-# CHECK-NEXT: ldr x1, [x1, #0x18]
+# CHECK-NEXT: ldr x1, [x1, #0x20]
# CHECK-NEXT: adrp x16, 4 ; 0x100004000
# CHECK-NEXT: ldr x16, [x16]
# CHECK-NEXT: br x16
@@ -44,13 +45,13 @@
# FASTALIGN-NEXT: align 2^5 (32)
# SMALL: _objc_msgSend$foo:
-# SMALL-NEXT: adrp x1, 4 ; 0x100004000
-# SMALL-NEXT: ldr x1, [x1, #0x10]
+# SMALL-NEXT: adrp x1, 8 ; 0x100008000
+# SMALL-NEXT: ldr x1, [x1, #0x18]
# SMALL-NEXT: b
# SMALL-NEXT: _objc_msgSend$length:
-# SMALL-NEXT: adrp x1, 4 ; 0x100004000
-# SMALL-NEXT: ldr x1, [x1, #0x18]
+# SMALL-NEXT: adrp x1, 8 ; 0x100008000
+# SMALL-NEXT: ldr x1, [x1, #0x20]
# SMALL-NEXT: b
# SMALLALIGN: sectname __objc_stubs
@@ -60,6 +61,12 @@
# SMALLALIGN-NEXT: offset
# SMALLALIGN-NEXT: align 2^2 (4)
+## Check correct section ordering
+# SECTIONS: Sections:
+# SECTIONS: __text
+# SECTIONS: __stubs
+# SECTIONS: __objc_stubs
+
.section __TEXT,__objc_methname,cstring_literals
lselref1:
.asciz "foo"
@@ -81,4 +88,5 @@ _main:
bl _objc_msgSend$length
bl _objc_msgSend$foo
bl _objc_msgSend$foo
+ bl _external_func
ret
``````````
</details>
https://github.com/llvm/llvm-project/pull/134010
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