[lld] r321986 - [ELF] Compress debug sections after assignAddresses and support custom layout
James Henderson via llvm-commits
llvm-commits at lists.llvm.org
Mon Jan 8 02:17:03 PST 2018
Author: jhenderson
Date: Mon Jan 8 02:17:03 2018
New Revision: 321986
URL: http://llvm.org/viewvc/llvm-project?rev=321986&view=rev
Log:
[ELF] Compress debug sections after assignAddresses and support custom layout
Previously, in r320472, I moved the calculation of section offsets and sizes
for compressed debug sections into maybeCompress, which happens before
assignAddresses, so that the compression had the required information. However,
I failed to take account of relocations that patch such sections. This had two
effects:
1. A race condition existed when a debug section referred to a different debug
section (see PR35788).
2. References to symbols in non-debug sections would be patched incorrectly.
This is because the addresses of such symbols are not calculated until after
assignAddresses (this was a partial regression caused by r320472, but they
could still have been broken before, in the event that a custom layout was used
in a linker script).
assignAddresses does not need to know about the output section size of
non-allocatable sections, because they do not affect the value of Dot. This
means that there is no longer a reason not to support custom layout of
compressed debug sections, as far as I'm aware. These two points allow for
delaying when maybeCompress can be called, removing the need for the loop I
previously added to calculate the section size, and therefore the race
condition. Furthermore, by delaying, we fix the issues of relocations getting
incorrect symbol values, because they have now all been finalized.
Added:
lld/trunk/test/ELF/Inputs/compress-debug.s
lld/trunk/test/ELF/compress-debug-sections-reloc.s
lld/trunk/test/ELF/linkerscript/compress-debug-sections-custom.s
Modified:
lld/trunk/ELF/LinkerScript.cpp
lld/trunk/ELF/OutputSections.cpp
lld/trunk/ELF/Writer.cpp
Modified: lld/trunk/ELF/LinkerScript.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/LinkerScript.cpp?rev=321986&r1=321985&r2=321986&view=diff
==============================================================================
--- lld/trunk/ELF/LinkerScript.cpp (original)
+++ lld/trunk/ELF/LinkerScript.cpp Mon Jan 8 02:17:03 2018
@@ -669,11 +669,6 @@ void LinkerScript::assignOffsets(OutputS
switchTo(Sec);
- // We do not support custom layout for compressed debug sectons.
- // At this point we already know their size and have compressed content.
- if (Ctx->OutSec->Flags & SHF_COMPRESSED)
- return;
-
// The Size previously denoted how many InputSections had been added to this
// section, and was used for sorting SHF_LINK_ORDER sections. Reset it to
// compute the actual size value.
Modified: lld/trunk/ELF/OutputSections.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.cpp?rev=321986&r1=321985&r2=321986&view=diff
==============================================================================
--- lld/trunk/ELF/OutputSections.cpp (original)
+++ lld/trunk/ELF/OutputSections.cpp Mon Jan 8 02:17:03 2018
@@ -183,15 +183,6 @@ template <class ELFT> void OutputSection
!Name.startswith(".debug_"))
return;
- // Calculate the section offsets and size pre-compression.
- Size = 0;
- for (BaseCommand *Cmd : SectionCommands)
- if (auto *ISD = dyn_cast<InputSectionDescription>(Cmd))
- for (InputSection *IS : ISD->Sections) {
- IS->OutSecOff = alignTo(Size, IS->Alignment);
- this->Size = IS->OutSecOff + IS->getSize();
- }
-
// Create a section header.
ZDebugHeader.resize(sizeof(Elf_Chdr));
auto *Hdr = reinterpret_cast<Elf_Chdr *>(ZDebugHeader.data());
Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=321986&r1=321985&r2=321986&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Mon Jan 8 02:17:03 2018
@@ -427,13 +427,14 @@ template <class ELFT> void Writer<ELFT>:
if (errorCount())
return;
+ Script->assignAddresses();
+
// If -compressed-debug-sections is specified, we need to compress
// .debug_* sections. Do it right now because it changes the size of
// output sections.
parallelForEach(OutputSections,
[](OutputSection *Sec) { Sec->maybeCompress<ELFT>(); });
- Script->assignAddresses();
Script->allocateHeaders(Phdrs);
// Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a
Added: lld/trunk/test/ELF/Inputs/compress-debug.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/Inputs/compress-debug.s?rev=321986&view=auto
==============================================================================
--- lld/trunk/test/ELF/Inputs/compress-debug.s (added)
+++ lld/trunk/test/ELF/Inputs/compress-debug.s Mon Jan 8 02:17:03 2018
@@ -0,0 +1,5 @@
+.text
+.fill 0x44
+
+.section .debug_info,"", at progbits
+.fill 0x43
Added: lld/trunk/test/ELF/compress-debug-sections-reloc.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/compress-debug-sections-reloc.s?rev=321986&view=auto
==============================================================================
--- lld/trunk/test/ELF/compress-debug-sections-reloc.s (added)
+++ lld/trunk/test/ELF/compress-debug-sections-reloc.s Mon Jan 8 02:17:03 2018
@@ -0,0 +1,26 @@
+# REQUIRES: x86, zlib
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %S/Inputs/compress-debug.s -o %t2.o
+# RUN: ld.lld %t2.o %t.o -o %t1 --compress-debug-sections=zlib -Ttext=0
+# RUN: llvm-dwarfdump %t1 -debug-str | FileCheck %s
+# These two checks correspond to the patched values of a_sym and a_debug_sym.
+# D = 0x44 - address of .text input section for this file (the start address of
+# .text is 0 as requested on the command line, and the size of the
+# preceding .text in the other input file is 0x44).
+# C = 0x43 - offset of .debug_info section for this file (the size of
+# the preceding .debug_info from the other input file is 0x43).
+# CHECK: 0x00000000: "D"
+# CHECK: 0x00000004: "C"
+
+.text
+a_sym:
+nop
+
+.section .debug_str,"", at progbits
+.long a_sym
+.long a_debug_sym
+
+.section .debug_info,"", at progbits
+a_debug_sym:
+.long 0x88776655
Added: lld/trunk/test/ELF/linkerscript/compress-debug-sections-custom.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/linkerscript/compress-debug-sections-custom.s?rev=321986&view=auto
==============================================================================
--- lld/trunk/test/ELF/linkerscript/compress-debug-sections-custom.s (added)
+++ lld/trunk/test/ELF/linkerscript/compress-debug-sections-custom.s Mon Jan 8 02:17:03 2018
@@ -0,0 +1,35 @@
+# REQUIRES: x86, zlib
+
+# RUN: echo "SECTIONS { \
+# RUN: .text : { . += 0x10; *(.text) } \
+# RUN: .debug_str : { . += 0x10; *(.debug_str) } \
+# RUN: .debug_info : { . += 0x10; *(.debug_info) } \
+# RUN: }" > %t.script
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %S/../Inputs/compress-debug.s -o %t2.o
+# RUN: ld.lld %t2.o %t.o -o %t1 --compress-debug-sections=zlib -T %t.script
+# RUN: llvm-dwarfdump %t1 -debug-str | FileCheck %s
+# These two checks correspond to the patched values of a_sym and a_debug_sym.
+# T = 0x54 - address of .text input section for this file (the start address of
+# .text is 0 by default, the size of the preceding .text in the other input
+# file is 0x44, and the linker script adds an additional 0x10).
+# S = 0x53 - offset of .debug_info section for this file (the size of
+# the preceding .debug_info from the other input file is 0x43, and the
+# linker script adds an additional 0x10).
+# Also note that the .debug_str offsets are also offset by 0x10, as directed by
+# the linker script.
+# CHECK: 0x00000010: "T"
+# CHECK: 0x00000014: "S"
+
+.text
+a_sym:
+nop
+
+.section .debug_str,"", at progbits
+.long a_sym
+.long a_debug_sym
+
+.section .debug_info,"", at progbits
+a_debug_sym:
+.long 0x88776655
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