[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 06:37:28 PST 2018
Hi Hans,
Could this commit be merged into the 6.0 release branch, as it fixes
PR35788.
Regards,
James Henderson
On 8 January 2018 at 10:17, James Henderson via llvm-commits <
llvm-commits at lists.llvm.org> wrote:
> 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/LinkerScri
> pt.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/OutputSect
> ions.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/Input
> s/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/compr
> ess-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/linke
> rscript/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
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180108/12cced7d/attachment.html>
More information about the llvm-commits
mailing list