Messages in this thread | | | Subject | Re: [GIT PULL] Modules updates for v5.12 | From | Rasmus Villemoes <> | Date | Thu, 25 Feb 2021 17:19:27 +0100 |
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On 25/02/2021 16.49, Masahiro Yamada wrote: > On Thu, Feb 25, 2021 at 4:36 AM Rasmus Villemoes > <rasmus.villemoes@prevas.dk> wrote: >> >> On 24/02/2021 15.40, Masahiro Yamada wrote: > > > Good insight. > Actually, I came up with the same idea last night, and had started > the implementation background. > I needed sleep before completing the patch set, but > now it is working as far as I tested. > > BTW, > KEEP(*(SORT(___ksymtab+foo ___ksymtab+bar ___ksymtab+baz)) > is a syntax error. >
ah, ok, didn't test anything, just threw it out there in case somebody wanted to see if it was doable.
Is that a limitation of SORT? The ld docs say
There are two ways to include more than one section: *(.text .rdata) *(.text) *(.rdata) The difference between these is the order in which the '.text' and '.rdata' input sections will appear in the output section.
so there shouldn't be a problem mentioning more than one section name?
>> If LD_DEAD_CODE_DATA_ELIMINATION was more widely supported (and I was >> surprised to see that it's not even available on arm or x86) one could >> also play another game, dropping the KEEP()s and instead create a linker >> script snippet containing EXTERN(__ksymtab_foo __ksymtab_bar ...), >> referencing the "struct kernel_symbol" elements themselves rather than >> the singleton sections they reside in. > > Do you mean LD_DEAD_CODE_DATA_ELIMINATION must be enabled by default > to do this? >
No, but without LD_DEAD_CODE_DATA_ELIMINATION, I don't see much point of the TRIM_UNUSED_KSYMS. Yes, the export_symbol metadata itself vanishes, but the actual functions remain in the image. Conversely, with modules enabled, LD_DEAD_CODE_DATA_ELIMINATION can't do much when almost all of the kernel can be built modular so almost extern interface is an EXPORT_SYMBOL. At least, that's what I see for a ppc target with a somewhat trimmed-down .config, combining the two gives much more space saving than the sum of what each option does:
$ size vmlinux.{vanilla,trim,dead,trim-dead} text data bss dec hex filename 6197380 1159488 121732 7478600 721d48 vmlinux.vanilla 6045906 1159440 121732 7327078 6fcd66 vmlinux.trim 6087316 1137284 120476 7345076 7013b4 vmlinux.dead 5675370 1101964 115180 6892514 692be2 vmlinux.trim-dead
Anyway, that was just an aside, probably the above ___ksymtab+foo thing will work just fine.
Rasmus
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