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[LLD][ELF] - Do not produce an invalid dynamic relocation order with --shuffle-sections.

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Normally (when not on android with android relocation packing enabled),
we put IRelative relocations to ".rel[a].dyn", after other relocations,
to ensure that IRelatives are processed last by the dynamic loader.

To achieve that we add the `in.relaIplt` after the `part.relaDyn`:
https://github.com/llvm/llvm-project/blob/master/lld/ELF/Writer.cpp#L540

The problem is that `--shuffle-sections` might break the sections order.
This patch fixes it.

Fixes https://bugs.llvm.org/show_bug.cgi?id=47056.

Differential revision: https://reviews.llvm.org/D85651
This commit is contained in:
Georgii Rymar 2020-08-10 17:00:53 +03:00
parent 7e6c437fb4
commit c135a68d42
2 changed files with 22 additions and 0 deletions
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8
lld/ELF/Writer.cpp
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@ -1437,6 +1437,14 @@ static void sortSection(OutputSection *sec,
if (name == ".init" || name == ".fini")
return;
// IRelative relocations that usually live in the .rel[a].dyn section should
// be proccessed last by the dynamic loader. To achieve that we add synthetic
// sections in the required order from the begining so that the in.relaIplt
// section is placed last in an output section. Here we just do not apply
// sorting for an output section which holds the in.relaIplt section.
if (in.relaIplt->getParent() == sec)
return;
// Sort input sections by priority using the list provided by
// --symbol-ordering-file or --shuffle-sections=. This is a least significant
// digit radix sort. The sections may be sorted stably again by a more

14
lld/test/ELF/gnu-ifunc-plt.s
View File

@ -77,6 +77,20 @@
// DISASM-NEXT: 201386: pushq $0x1
// DISASM-NEXT: 20138b: jmp 0x201340 <.plt>
// Test that --shuffle-sections does not affect the order of relocations and that
// we still place IRELATIVE relocations last. Check both random seed (0) and an
// arbitrary seed that was known to break the order of relocations previously (3).
// RUN: ld.lld --shuffle-sections=3 %t.so %t.o -o %tout2
// RUN: llvm-readobj --relocations %tout2 | FileCheck %s --check-prefix=SHUFFLE
// RUN: ld.lld --shuffle-sections=0 %t.so %t.o -o %tout3
// RUN: llvm-readobj --relocations %tout3 | FileCheck %s --check-prefix=SHUFFLE
// SHUFFLE: Section {{.*}} .rela.dyn {
// SHUFFLE-NEXT: R_X86_64_GLOB_DAT
// SHUFFLE-NEXT: R_X86_64_IRELATIVE
// SHUFFLE-NEXT: R_X86_64_IRELATIVE
// SHUFFLE-NEXT: }
.text
.type foo STT_GNU_IFUNC
.globl foo