[PATCH] D67152: Align output segments correctly
Rui Ueyama via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 4 04:10:49 PDT 2019
ruiu created this revision.
ruiu added reviewers: MaskRay, peter.smith, grimar.
Herald added subscribers: arichardson, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.
Previously, segments were aligned according to their first section's
alignment requirements. That was not correct, but segments are also
aligned to a page boundary, and a page boundary is usually much larger
than a section alignment requirement, so no one noticed this bug before.
Now, lld has --nmagic option which sets maxPageSize to 1 to effectively
disable page alignment, which reveals the issue.
Fixes https://bugs.llvm.org/show_bug.cgi?id=43212
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D67152
Files:
lld/ELF/Writer.cpp
lld/test/ELF/nmagic.s
Index: lld/test/ELF/nmagic.s
===================================================================
--- /dev/null
+++ lld/test/ELF/nmagic.s
@@ -0,0 +1,23 @@
+# REQUIRES: x86
+# Verify that .rodata is aligned to a 8 byte boundary.
+
+# RUN: llvm-mc -filetype=obj -triple=i386-unknown-linux %s -o %t.o
+# RUN: ld.lld %t.o -o %t.exe -N -Ttext 0
+# RUN: llvm-readelf -section-headers %t.exe | FileCheck %s
+
+# CHECK: [ 0] NULL 00000000 000000 000000 00 0 0 0
+# CHECK: [ 1] .text PROGBITS 00000000 000098 000001 00 AX 0 0 4
+# CHECK: [ 2] .rodata PROGBITS 00000008 0000a0 000008 00 A 0 0 8
+# CHECK: [ 3] .comment PROGBITS 00000000 0000a8 000008 01 MS 0 0 1
+# CHECK: [ 4] .symtab SYMTAB 00000000 0000b0 000020 10 6 1 4
+# CHECK: [ 5] .shstrtab STRTAB 00000000 0000d0 000032 00 0 0 1
+# CHECK: [ 6] .strtab STRTAB 00000000 000102 000008 00 0 0 1
+
+.globl _start
+.text
+_start:
+ ret
+
+.rodata
+.align 8
+.quad 42
Index: lld/ELF/Writer.cpp
===================================================================
--- lld/ELF/Writer.cpp
+++ lld/ELF/Writer.cpp
@@ -2272,7 +2272,8 @@
// The first section in a PT_LOAD has to have congruent offset and address
// module the page size.
if (os->ptLoad && os->ptLoad->firstSec == os) {
- uint64_t alignment = std::max<uint64_t>(os->alignment, config->maxPageSize);
+ uint64_t alignment =
+ std::max<uint64_t>(os->ptLoad->p_align, config->maxPageSize);
return alignTo(off, alignment, os->addr);
}
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