Messages in this thread | | | Date | Mon, 24 Feb 2020 14:50:59 -0800 | From | Fangrui Song <> | Subject | Re: [PATCH 2/2] x86/boot/compressed: Remove unnecessary sections from bzImage |
| |
On 2020-02-24, Arvind Sankar wrote: >On Mon, Feb 24, 2020 at 02:17:03PM -0800, Fangrui Song wrote: >> On 2020-02-24, Arvind Sankar wrote: >> >On Mon, Feb 24, 2020 at 01:28:28PM -0800, Fangrui Song wrote: >> >> Hi Michael, please see my other reply on this thread: https://lkml.org/lkml/2020/2/24/47 >> >> >> >> Synthesized sections can be matched as well. For example, SECTIONS { .pltfoo : { *(.plt) }} can rename the output section .plt to .pltfoo >> >> It seems that in GNU ld, the synthesized section is associated with the >> >> original object file, so it can be written as: >> >> >> >> SECTIONS { .pltfoo : { a.o(.plt) }} >> >> >> >> In lld, you need a wildcard to match the synthesized section *(.plt) >> >> >> >> .rela.dyn is another example. >> >> >> > >> >With the BFD toolchain, file matching doesn't actually seem to work at >> >least for .rela.dyn. I've tried playing around with it in the past and >> >if you try to use file-matching to capture relocations from a particular >> >input file, it just doesn't work sensibly. >> >> I think most things are working in GNU ld... >> >> /* a.x */ >> SECTIONS { >> .rela.pltfoo : { a.o(.rela.plt) } /* *(.rela.plt) with lld */ >> .rela.dynfoo : { a.o(.rela.data) } /* *(.rela.dyn) with lld */ >> } > >The file matching doesn't do anything sensible. If you split your .data >section out into b.s, and update the linker script so it filters for >b.o(.rela.data), .rela.dynfoo doesn't get created, instead the default >.rela.dyn will contains the .data section relocation. If you keep the >filter as a.o(.rela.data), you get .rela.dynfoo, even though a.o doesn't >actually contain any .rela.data section any more.
I raised the examples to support my viewpoint "synthesized sections can be matched, as well as input sections."
If there is really a need (rare, not recommended) to rename output sections only consisting of synthesized sections (e.g. .plt .rela.dyn), for linker portability, it is better using a wildcard for the input filename pattern.
As another example, SECTIONS { /DISCARD/ : { *(.rela.*) } } discards synthesized .rela.*
>> >> % cat <<e > a.s >> .globl foo >> foo: >> call bar >> .data >> .quad quz >> e >> % as a.s -o a.o >> % ld.bfd -T a.x a.o -shared -o a.so
| |