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[ELF] Align SHT_LLVM_PART_EHDR to a maximum page size boundary 

Fixes https://bugs.chromium.org/p/chromium/issues/detail?id=998712

SHT_LLVM_PART_EHDR marks the start of a partition. The partition
sections will be extracted to a separate file. Align to the next maximum
page size boundary so that we can find the ELF header at the start. We
cannot benefit from overlapping p_offset ranges with the previous
segment anyway.

It seems we lack some llvm-objcopy --extract-main-partition and
--extract-partition sanity checks. It may place EHDR at the start
even if p_offset if non zero. Anyway, the lld change is justified for
the reasons above.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D67032

llvm-svn: 370629
This commit is contained in:
Fangrui Song 2019-09-02 08:49:50 +00:00
parent 6897a814e6
commit 4514ac7cfb
2 changed files with 25 additions and 10 deletions
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12
lld/ELF/Writer.cpp
View File

@ -2223,13 +2223,21 @@ template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
// the next maximum page size boundary on transitions between executable
// and non-executable segments.
//
// SHT_LLVM_PART_EHDR marks the start of a partition. The partition
// sections will be extracted to a separate file. Align to the next
// maximum page size boundary so that we can find the ELF header at the
// start. We cannot benefit from overlapping p_offset ranges with the
// previous segment anyway.
//
// TODO Enable this technique on all targets.
bool enable = config->emachine != EM_HEXAGON &&
config->emachine != EM_MIPS &&
config->emachine != EM_X86_64;
if (!enable || (config->zSeparateCode && prev &&
(prev->p_flags & PF_X) != (p->p_flags & PF_X)))
if (!enable ||
(config->zSeparateCode && prev &&
(prev->p_flags & PF_X) != (p->p_flags & PF_X)) ||
cmd->type == SHT_LLVM_PART_EHDR)
cmd->addrExpr = [] {
return alignTo(script->getDot(), config->maxPageSize);
};

23
lld/test/ELF/partitions.s
View File

@ -1,13 +1,20 @@
// REQUIRES: x86
// REQUIRES: aarch64, x86
// RUN: llvm-mc %s -o %t.o -filetype=obj --triple=x86_64-unknown-linux
// RUN: ld.lld %t.o -o %t --export-dynamic --gc-sections -z max-page-size=65536
// RUN: llvm-readelf -S -s %t | FileCheck %s
// RUN: llvm-mc %s -o %t.o -filetype=obj --triple=aarch64
// RUN: ld.lld %t.o -o %t --export-dynamic --gc-sections
// RUN: llvm-readelf -S -s %t | FileCheck %s
// This is basically lld/docs/partitions.dot in object file form.
// Test that the sections are correctly allocated to partitions.
// part1 and part2 should be aligned to a maximum page size boundary.
// CHECK: [[MAIN:[0-9]+]]] .text
// CHECK: part1 LOOS+0xFFF4C06 {{[0-9a-f]+}}0000 {{[0-9a-f]+}}0000
// CHECK: [[P1:[0-9]+]]] .text
// CHECK: part2 LOOS+0xFFF4C06 {{[0-9a-f]+}}0000 {{[0-9a-f]+}}0000
// CHECK: [[P2:[0-9]+]]] .text
// CHECK: Symbol table '.symtab'
@ -30,21 +37,21 @@
.section .text._start,"ax",@progbits
.globl _start
_start:
call f3
.quad f3
.section .text.f1,"ax",@progbits
.globl f1
f1:
call f3
call f4
call f5
.quad f3
.quad f4
.quad f5
.section .text.f2,"ax",@progbits
.globl f2
f2:
call f3
call f5
call f6
.quad f3
.quad f5
.quad f6
.section .text.f3,"ax",@progbits
f3: