[lld-macho] Handle alignment correctly when merging InputSections

[int3]

Summary

Previously, we weren't updating isecAddr when aligning InputSections,
resulting in truncated sections under the right conditions.

[int3]

rename i -> isec for consistency

[compnerd]

lld/test/MachO/section-merge.s

16

Where is ADDR captured? I can't seem to spot it.

[int3]

lld/test/MachO/section-merge.s

16

it's captured on line 13

[compnerd]

Ah, somehow I inverted the application and read it as a check rather than capture, thanks!

[smeenai]

The fix and test for it look good, but the previous test was also checking that section contents were being merged correctly, which is being dropped. Could you add that back?

[int3]

check that section contents are being merged correctly

[int3]

@smeenai Oh yeah good point. I've added some nonzero data to the data section, so it can double up as a check for the correctness of the contents too. Just wanted to make the test as compact as possible

[int3]

update

lld/MachO/MergedOutputSection.cpp

void MergedOutputSection::mergeInput(InputSection *input) {
 
   inputs.push_back(input);
   input->parent = this;
 }
 
 void MergedOutputSection::finalize() {
   uint64_t isecAddr = addr;
   uint64_t isecFileOff = fileOff;
-  for (InputSection *i : inputs) {
-    i->outSecOff = alignTo(isecAddr, i->align) - addr;
-    i->outSecFileOff = alignTo(isecFileOff, i->align) - fileOff;
-    isecAddr += i->getSize();
-    isecFileOff += i->getFileSize();
+  for (InputSection *isec : inputs) {
+    isecAddr = alignTo(isecAddr, isec->align);
+    isecFileOff = alignTo(isecFileOff, isec->align);
+    isec->outSecOff = isecAddr - addr;
+    isec->outSecFileOff = isecFileOff - fileOff;
+    isecAddr += isec->getSize();
+    isecFileOff += isec->getFileSize();
   }
   size = isecAddr - addr;
   fileSize = isecFileOff - fileOff;
 }
 
 void MergedOutputSection::writeTo(uint8_t *buf) const {
   for (InputSection *isec : inputs) {
     isec->writeTo(buf + isec->outSecFileOff);

lld/test/MachO/section-merge.s

 # REQUIRES: x86
 # RUN: mkdir -p %t
-# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %p/Inputs/libhello.s \
-# RUN:   -o %t/libhello.o
-# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %p/Inputs/libgoodbye.s \
-# RUN:   -o %t/libgoodbye.o
-# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %p/Inputs/libfunction.s \
-# RUN:   -o %t/libfunction.o
-# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s \
-# RUN:   -o %t/main.o
-# RUN: lld -flavor darwinnew -o %t/output %t/libfunction.o %t/libgoodbye.o %t/libhello.o %t/main.o
+## Verify that we preserve alignment when merging sections.
+# RUN: echo ".globl _foo; .data; .p2align 0; _foo: .space 1" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/foo.o
+# RUN: echo ".globl _bar; .data; .p2align 2; _bar: .space 1" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/bar.o
+# RUN: echo ".globl _baz; .data; .p2align 3; _baz: .space 1" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/baz.o
+# RUN: echo ".globl _qux; .data; .p2align 0; _qux: .space 1" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/qux.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/main.o
+# RUN: lld -flavor darwinnew -o %t/output %t/foo.o %t/bar.o %t/baz.o %t/qux.o %t/main.o
 
 # RUN: llvm-objdump --syms %t/output | FileCheck %s
-# CHECK:      SYMBOL TABLE:
-# CHECK-DAG:  {{[0-9a-z]+}} g     O __TEXT,__cstring _goodbye_world
-# CHECK-DAG:  {{[0-9a-z]+}} g     O __TEXT,__cstring _hello_its_me
-# CHECK-DAG:  {{[0-9a-z]+}} g     O __TEXT,__cstring _hello_world
-# CHECK-DAG:  {{[0-9a-z]+}} g     F __TEXT,__text _main
-# CHECK-DAG:  {{[0-9a-z]+}} g     F __TEXT,__text _some_function
-
-# RUN: llvm-objdump -d %t/output | FileCheck %s --check-prefix DATA
-# DATA:      Disassembly of section __TEXT,__text:
-# DATA:        {{0*}}[[#%x,BASE:]] <_some_function>:
-# DATA-NEXT:             [[#BASE]]: 48 c7 c0 01 00 00 00          movq    $1, %rax
-# DATA-NEXT:       [[#BASE + 0x7]]: c3                            retq
-# DATA:        {{0*}}[[#%x,MAIN:]] <_main>:
-# DATA-NEXT:             [[#MAIN]]: 48 c7 c0 00 00 00 00          movq    $0, %rax
-# DATA-NEXT:       [[#MAIN + 0x7]]: c3                            retq
+# CHECK:     SYMBOL TABLE:
+# CHECK-DAG: [[#%x, ADDR:]]      g     O __DATA,__data _foo
+# CHECK-DAG: {{0*}}[[#ADDR+0x4]] g     O __DATA,__data _bar
+# CHECK-DAG: {{0*}}[[#ADDR+0x8]] g     O __DATA,__data _baz
+# CHECK-DAG: {{0*}}[[#ADDR+0x9]] g     O __DATA,__data _qux
 
 .section __TEXT,__text
 .global _main
 
 _main:
   mov $0, %rax
   ret