[PATCH] D65242: [ELF] More dynamic relocation packing

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

In D65242#1638794 <https://reviews.llvm.org/D65242#1638794>, @grimar wrote:

> In D65242#1638787 <https://reviews.llvm.org/D65242#1638787>, @MaskRay wrote:
>
> > Weird. http://lab.llvm.org:8011/builders/lld-x86_64-freebsd/builds/34407/steps/test_lld/logs/stdio (http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap-ubsan/builds/14511/steps/check-lld%20ubsan/logs/stdio has a similar error message)
> >
> >   /usr/home/buildslave/as-bldslv5/lld-x86_64-freebsd/llvm.src/tools/lld/test/ELF/pack-dyn-relocs.s:106:20: error: ANDROID32-NEXT: is not on the line after the previous match
> >   // ANDROID32-NEXT: 0x2044 R_ARM_ABS32 bar2 0x0
> >                      ^
> >   <stdin>:36:2: note: 'next' match was here
> >    0x2044 R_ARM_ABS32 bar2 0x0
> >    ^
> >   <stdin>:34:29: note: previous match ended here
> >    0x2020 R_ARM_ABS32 bar2 0x0
> >                               ^
> >   <stdin>:35:1: note: non-matching line after previous match is here
> >    0x2040 R_ARM_ABS32 zed2 0x0
> >
>
>
> I wonder if `llvm::sort` instead of stable sort can be the reason?


Probably not? I tried this before reverting...

  @@ -38,6 +38,7 @@
   #include "llvm/Support/MD5.h"
   #include <cstdlib>
   #include <thread>
  +#include <random>
   
   using namespace llvm;
   using namespace llvm::dwarf;
  @@ -1676,7 +1677,9 @@ bool AndroidPackedRelocationSection<ELFT>::updateAllocSize() {
       else
         nonRelatives.push_back(r);
     }
  +  std::mt19937 Generator(std::random_device{}());
   
  +  std::shuffle(relatives.begin(), relatives.end(), Generator);
     llvm::sort(relatives, [](const Elf_Rel &a, const Elf_Rel &b) {
       return a.r_offset < b.r_offset;
     });
  @@ -1747,6 +1750,7 @@ bool AndroidPackedRelocationSection<ELFT>::updateAllocSize() {
       i = j;
     }
   
  +  std::shuffle(ungroupedNonRelatives.begin(), ungroupedNonRelatives.end(), Generator);
     // Sort ungrouped relocations by offset to minimize the encoded length.
     llvm::sort(ungroupedNonRelatives, [](const Elf_Rela &a, const Elf_Rela &b) {
       return a.r_offset < b.r_offset;


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  https://reviews.llvm.org/D65242/new/

https://reviews.llvm.org/D65242