| Summary: | Extreme assembling time regression with 2.35 and master | ||
|---|---|---|---|
| Product: | binutils | Reporter: | franz.sirl |
| Component: | gas | Assignee: | Nick Clifton <nickc> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | amodra, franz.sirl, mail, martin.liska, nickc, romain.geissler |
| Priority: | P2 | ||
| Version: | 2.35 | ||
| Target Milestone: | --- | ||
| Host: | x86_64-linux-gnu | Target: | x86_64-linux-gnu |
| Build: | x86_64-linux-gnu | Last reconfirmed: | |
| Attachments: | Proposed patch | ||
|
Description
franz.sirl
2020-08-19 12:41:24 UTC
We're quadratic in number of sections. _bfd_elf_write_object_contents bfd_map_over_sections (abfd, bed->s->write_relocs, &failed); elf_write_relocs: if (!bed->write_secondary_relocs (abfd, sec)) _bfd_elf_write_secondary_reloc_section: for (relsec = abfd->sections; relsec != NULL; relsec = relsec->next) Well, that would explain it: fsirl@ds1:~> grep '\.section' ~/sample.s |sort -u|wc -l 294085 The testcase was compiled with -ffunction-sections -fdata-sections. Created attachment 12781 [details]
Proposed patch
Hi Franz,
Please could you try out this patch and let me know if it works for you.
It will only improve the performance in the case of linking files which
do not contain secondary relocs, but I am assuming that this applies to
you.
A proper fix, involving chaining the secondary reloc sections together
should be written some day, but for now I am hoping that this will do.
(Ideally the BFD library's whole support infrastructure for relocs
should be rewritten, but that is a huge project).
Cheers
Nick
Hi Nick, yes, I can confirm that your patch brings back the performance to the original level. Thanks, Franz The master branch has been updated by Nick Clifton <nickc@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=44466e45c51b1c68ed2f95f86bcdb1f18f08b380 commit 44466e45c51b1c68ed2f95f86bcdb1f18f08b380 Author: Nick Clifton <nickc@redhat.com> Date: Thu Aug 20 10:19:47 2020 +0100 Apply a workaround to mitigate a quadratic performance hit in the linker when writing out secondary reloc sections. PR 26406 * elf-bfd.h (struct bfd_elf_section_data): Add has_secondary_relocs field. * elf.c (_bfd_elf_copy_special_section_fields): Set the has_secondary_relocs field for sections which have associated secondary relocs. * elfcode.h (elf_write_relocs): Only call write_secondary_relocs on sections which have associated secondary relocs. Patch applied. Hi Nick, Now that it has been in master for roughly 10 days, shall this be considered for a backport in the release branch 2.35 ? Cheers, Romain The binutils-2_35-branch branch has been updated by Nick Clifton <nickc@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=790244d25897928fd5c950ee4e4ef84e3e9fd6ed commit 790244d25897928fd5c950ee4e4ef84e3e9fd6ed Author: Nick Clifton <nickc@redhat.com> Date: Thu Sep 3 16:00:48 2020 +0100 Partially fix a quadratic slowdown when processing secondary relocations for inputs with lots of sections. PR 26406 * elf-bfd.h (struct bfd_elf_section_data): Add has_secondary_relocs field. * elf.c (_bfd_elf_copy_special_section_fields): Set the has_secondary_relocs field for sections which have associated secondary relocs. * elfcode.h (elf_write_relocs): Only call write_secondary_relocs on sections which have associated secondary relocs. (In reply to Romain Geissler from comment #7) > Now that it has been in master for roughly 10 days, shall this be considered > for a backport in the release branch 2.35 ? Done. |