[lld] r332589 - [ELF] - Do not crash when do --gc-sections for non-allocatable metadata sections.
George Rimar via llvm-commits
llvm-commits at lists.llvm.org
Thu May 17 03:00:34 PDT 2018
Author: grimar
Date: Thu May 17 03:00:34 2018
New Revision: 332589
URL: http://llvm.org/viewvc/llvm-project?rev=332589&view=rev
Log:
[ELF] - Do not crash when do --gc-sections for non-allocatable metadata sections.
Currently, LLD marks all non-allocatable sections except SHF_REL[A] as Live
when doing GC.
This can be a reason of the crash when SHF_LINK_ORDER sections
are involved, because their parents can be dead.
We should do GC for them correctly. The patch implements it.
Differential revision: https://reviews.llvm.org/D46880
Added:
lld/trunk/test/ELF/non-alloc-link-order-gc.s
Modified:
lld/trunk/ELF/MarkLive.cpp
Modified: lld/trunk/ELF/MarkLive.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/MarkLive.cpp?rev=332589&r1=332588&r2=332589&view=diff
==============================================================================
--- lld/trunk/ELF/MarkLive.cpp (original)
+++ lld/trunk/ELF/MarkLive.cpp Thu May 17 03:00:34 2018
@@ -275,13 +275,18 @@ template <class ELFT> void elf::markLive
// The -gc-sections option works only for SHF_ALLOC sections
// (sections that are memory-mapped at runtime). So we can
- // unconditionally make non-SHF_ALLOC sections alive.
+ // unconditionally make non-SHF_ALLOC sections alive except
+ // SHF_LINK_ORDER and SHT_REL/SHT_RELA sections.
//
- // Non SHF_ALLOC sections are not removed even if they are
+ // Usually, SHF_ALLOC sections are not removed even if they are
// unreachable through relocations because reachability is not
// a good signal whether they are garbage or not (e.g. there is
// usually no section referring to a .comment section, but we
- // want to keep it.)
+ // want to keep it.).
+ //
+ // Note on SHF_LINK_ORDER: Such sections contain metadata and they
+ // have a reverse dependency on the InputSection they are linked with.
+ // We are able to garbage collect them.
//
// Note on SHF_REL{,A}: Such sections reach here only when -r
// or -emit-reloc were given. And they are subject of garbage
@@ -289,8 +294,9 @@ template <class ELFT> void elf::markLive
// remove its relocation section.
for (InputSectionBase *Sec : InputSections) {
bool IsAlloc = (Sec->Flags & SHF_ALLOC);
+ bool IsLinkOrder = (Sec->Flags & SHF_LINK_ORDER);
bool IsRel = (Sec->Type == SHT_REL || Sec->Type == SHT_RELA);
- if (!IsAlloc && !IsRel)
+ if (!IsAlloc && !IsLinkOrder && !IsRel)
Sec->Live = true;
}
Added: lld/trunk/test/ELF/non-alloc-link-order-gc.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/non-alloc-link-order-gc.s?rev=332589&view=auto
==============================================================================
--- lld/trunk/test/ELF/non-alloc-link-order-gc.s (added)
+++ lld/trunk/test/ELF/non-alloc-link-order-gc.s Thu May 17 03:00:34 2018
@@ -0,0 +1,34 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: ld.lld %t.o -o %t1 --gc-sections
+# RUN: llvm-objdump -section-headers -D %t1 | FileCheck %s
+
+## Check that we are able to GC non-allocatable metadata sections without crash.
+
+# CHECK: Disassembly of section .stack_sizes:
+# CHECK-NEXT: .stack_sizes:
+# CHECK-NEXT: 01
+
+# CHECK: Name Size
+# CHECK: .stack_sizes 00000001
+
+.section .text.live,"ax", at progbits
+.globl live
+live:
+ nop
+
+.section .stack_sizes,"o", at progbits,.text.live,unique,0
+.byte 1
+
+.section .text.dead,"ax", at progbits
+.globl dead
+dead:
+ nop
+
+.section .stack_sizes,"o", at progbits,.text.dead,unique,1
+.byte 2
+
+.section .text.main,"ax", at progbits
+.globl _start
+_start:
+ callq live at PLT
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