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[LLD][ELF] Allow empty (.init|.preinit|.fini)_array to be RELRO

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The default GNU linker script uses the following idiom for the array
sections. I'll use .init_array here, but this also applies to
.preinit_array and .fini_array sections.

  .init_array    :
  {
    PROVIDE_HIDDEN (__init_array_start = .);
    KEEP (*(.init_array))
    PROVIDE_HIDDEN (__init_array_end = .);
  }

The C-library will take references to the _start and _end symbols to
process the array. This will make LLD keep the OutputSection even if there
are no .init_array sections. As the current check for RELRO uses the
section type for .init_array the above example with no .init_array
InputSections fails the checks as there are no .init_array sections to give
the OutputSection a type of SHT_INIT_ARRAY. This often leads to a
non-contiguous RELRO error message.

The simple fix is to a textual section match as well as a section type
match.

Differential Revision: https://reviews.llvm.org/D76915
This commit is contained in:
Peter Smith 2020-03-27 10:15:02 +00:00
parent b37543750c
commit 2539b4ae47
2 changed files with 41 additions and 1 deletions
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3
lld/ELF/Writer.cpp
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@ -819,7 +819,8 @@ static bool isRelroSection(const OutputSection *sec) {
StringRef s = sec->name;
return s == ".data.rel.ro" || s == ".bss.rel.ro" || s == ".ctors" ||
s == ".dtors" || s == ".jcr" || s == ".eh_frame" ||
s == ".openbsd.randomdata";
s == ".fini_array" || s == ".init_array" ||
s == ".openbsd.randomdata" || s == ".preinit_array";
}
// We compute a rank for each section. The rank indicates where the

39
lld/test/ELF/relro-init-fini-script.s Normal file
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@ -0,0 +1,39 @@
// REQUIRES: x86
// RUN: llvm-mc -filetype=obj -triple=x86_64-none-elf %s -o %t.o
// RUN: echo "SECTIONS { \
// RUN: .dynamic 0x10000 : { *(.dynamic) } \
// RUN: .preinit_array : { PROVIDE_HIDDEN (__preinit_array_start = .); \
// RUN: KEEP (*(.preinit_array)) } \
// RUN: .init_array : { PROVIDE_HIDDEN (__init_array_start = .); \
// RUN: KEEP (*(.init_array)) } \
// RUN: .fini_array : { PROVIDE_HIDDEN (__fini_array_start = .); \
// RUN: KEEP (*(.fini_array)) } \
// RUN: .data.rel.ro : { *(.data.rel.ro) } \
// RUN: .data : { *(.data) } } " > %t.script
// RUN: ld.lld %t.o -o %t.so --shared --script=%t.script
// RUN: llvm-readelf -S %t.so | FileCheck %s
// RUN: llvm-readobj --segments %t.so | FileCheck %s --check-prefix=PHDR
/// Check that an empty .init_array, .fini_array or .preinit_array that is
/// kept due to symbol references, is still counted as RELRO. The _array
/// sections are zero size. The RELRO extent is [.dynamic, .data.rel.ro)
// CHECK: .dynamic DYNAMIC 0000000000010000 002000 000110
// CHECK-NEXT: .preinit_array PROGBITS {{0+}}[[# %x,ADDR:]]
// CHECK-NEXT: .init_array PROGBITS {{0+}}[[# ADDR]]
// CHECK-NEXT: .fini_array PROGBITS {{0+}}[[# ADDR]]
// CHECK-NEXT: .data.rel.ro PROGBITS 0000000000010110 002110 000008
// PHDR: Type: PT_GNU_RELRO
// PHDR-NEXT: Offset: 0x2000
// PHDR-NEXT: VirtualAddress: 0x10000
// PHDR-NEXT: PhysicalAddress: 0x10000
// PHDR-NEXT: FileSize: 280
.section .data.rel.ro, "aw", %progbits
.global foo
.quad foo
.data
.quad __init_array_start
.quad __fini_array_start
.quad __preinit_array_start