There was a discussion https://groups.google.com/d/msg/generic-abi/_CbBM6T6WeM/9nNnwRNHAQAJ to extend the semantics of SHF_LINK_ORDER to represent metadata sections. All parties were in favor of the the wording: ... Furthermore, relocations from this section into the referenced section should not be taken as evidence that the referenced section should be retained. The patch https://sourceware.org/ml/binutils/2017-04/msg00000.html was posted, but doesn't seem to have been applied yet. Projects thay may benefit from it: Linux kernel https://lwn.net/Articles/741617/ LLVM !associated metadata https://llvm.org/docs/LangRef.html#associated-metadata
This is a feature request to both GNU ld and gold. # a.s .globl _start _start: .quad .foo .section .foo,"a" .quad 0 .section .bar,"ao",@progbits,.foo .quad 0 .section .zed,"ao",@progbits,.foo .quad 0 llvm-mc -filetype=obj -triple=x86_64 a.s -o a.o ld.bfd --gc-sections a.o -o a; readelf -S a # .bar and .zed were collected gold --gc-sections a.o -o a; readelf -S a # .bar and .zed were collected ld.lld --gc-sections a.o -o a; readelf -S a # .bar and .zed were retained In lld, the SHF_LINK_ORDER sections .bar and .zed are treated like .rela.foo. The retain of .foo will also keep .bar and .zed alive.
Ld bug is tracked by PR ld/25490.
The master branch has been updated by H.J. Lu <hjl@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=b7d072167715829eed0622616f6ae0182900de3e commit b7d072167715829eed0622616f6ae0182900de3e Author: H.J. Lu <hjl.tools@gmail.com> Date: Thu Feb 6 18:04:58 2020 -0800 ELF: Support the section flag 'o' in .section directive As shown in https://sourceware.org/bugzilla/show_bug.cgi?id=25490 --gc-sections will silently remove __patchable_function_entries section and generate corrupt result. This patch adds the section flag 'o' to .section directive: .section __patchable_function_entries,"awo",@progbits,foo .section __patchable_function_entries,"awoG",@progbits,foo,foo,comdat .section __patchable_function_entries,"awo",@progbits,bar,unique,4 .section __patchable_function_entries,"awoG",@progbits,foo,foo,comdat,unique,1 which specifies the symbol name which the section references. Assmebler will set its elf_linked_to_section to a local section where the symbol is defined. Linker is updated to call mark_hook if gc_mark of any of its linked-to sections is set after all sections, except for backend specific ones, have been garbage collected. bfd/ PR gas/25381 * bfd-in2.h: Regenerated. * elflink.c (_bfd_elf_gc_mark_extra_sections): Call mark_hook on section if gc_mark of any of its linked-to sections is set and don't set gc_mark again. * section.c (asection): Add linked_to_symbol_name to map_head union. gas/ PR gas/25381 * config/obj-elf.c (get_section): Also check linked_to_symbol_name. (obj_elf_change_section): Also set map_head.linked_to_symbol_name. (obj_elf_parse_section_letters): Handle the 'o' flag. (build_group_lists): Renamed to ... (build_additional_section_info): This. Set elf_linked_to_section from map_head.linked_to_symbol_name. (elf_adjust_symtab): Updated. * config/obj-elf.h (elf_section_match): Add linked_to_symbol_name. * doc/as.texi: Document the 'o' flag. * testsuite/gas/elf/elf.exp: Run PR gas/25381 tests. * testsuite/gas/elf/section18.d: New file. * testsuite/gas/elf/section18.s: Likewise. * testsuite/gas/elf/section19.d: Likewise. * testsuite/gas/elf/section19.s: Likewise. * testsuite/gas/elf/section20.d: Likewise. * testsuite/gas/elf/section20.s: Likewise. * testsuite/gas/elf/section21.d: Likewise. * testsuite/gas/elf/section21.l: Likewise. * testsuite/gas/elf/section21.s: Likewise. ld/ PR ld/24526 PR ld/25021 PR ld/25490 * testsuite/ld-elf/elf.exp: Run PR ld/25490 tests. * testsuite/ld-elf/pr24526.d: New file. * testsuite/ld-elf/pr24526.s: Likewise. * testsuite/ld-elf/pr25021.d: Likewise. * testsuite/ld-elf/pr25021.s: Likewise. * testsuite/ld-elf/pr25490-2-16.rd: Likewise. * testsuite/ld-elf/pr25490-2-32.rd: Likewise. * testsuite/ld-elf/pr25490-2-64.rd: Likewise. * testsuite/ld-elf/pr25490-2.s: Likewise. * testsuite/ld-elf/pr25490-3-16.rd: Likewise. * testsuite/ld-elf/pr25490-3-32.rd: Likewise. * testsuite/ld-elf/pr25490-3-64.rd: Likewise. * testsuite/ld-elf/pr25490-3.s: Likewise. * testsuite/ld-elf/pr25490-4-16.rd: Likewise. * testsuite/ld-elf/pr25490-4-32.rd: Likewise. * testsuite/ld-elf/pr25490-4-64.rd: Likewise. * testsuite/ld-elf/pr25490-4.s: Likewise. * testsuite/ld-elf/pr25490-5-16.rd: Likewise. * testsuite/ld-elf/pr25490-5-32.rd: Likewise. * testsuite/ld-elf/pr25490-5-64.rd: Likewise. * testsuite/ld-elf/pr25490-5.s: Likewise. * testsuite/ld-elf/pr25490-6-16.rd: Likewise. * testsuite/ld-elf/pr25490-6-32.rd: Likewise. * testsuite/ld-elf/pr25490-6-64.rd: Likewise. * testsuite/ld-elf/pr25490-6.s: Likewise.