Messages in this thread | | | Date | Thu, 31 Oct 2019 11:13:06 +0100 | From | Jessica Yu <> | Subject | Re: [PATCH 4/7] module: avoid code duplication in include/linux/export.h |
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+++ Rasmus Villemoes [29/10/19 22:11 +0100]: >On 29/10/2019 20.19, Jessica Yu wrote: >> +++ Rasmus Villemoes [27/09/19 13:07 +0200]: >>> On 27/09/2019 11.36, Masahiro Yamada wrote: >>>> >>>> A typical kernel configuration has 10K exported symbols, so it >>>> increases 10KB in rough estimation. >>>> >>>> I did not come up with a good idea to refactor it without increasing >>>> the code size. >>> >>> Can't we put the "aMS" flags on the __ksymtab_strings section? That >>> would make the empty strings free, and would also deduplicate the >>> USB_STORAGE string. And while almost per definition we don't have exact >>> duplicates among the names of exported symbols, we might have both a foo >>> and __foo, so that could save even more. >>> >>> I don't know if we have it already, but we'd need each arch to tell us >>> what symbol to use for @ in @progbits (e.g. % for arm). It seems most >>> are fine with @, so maybe a generic version could be >>> >>> #ifndef ARCH_SECTION_TYPE_CHAR >>> #define ARCH_SECTION_TYPE_CHAR "@" >>> #endif >>> >>> and then it would be >>> section("__ksymtab_strings,\"aMS\","ARCH_SECTION_TYPE_CHAR"progbits,1") >> >> FWIW, I've just tinkered with this, and unfortunately the strings >> don't get deduplicated for kernel modules :-( >> >> Apparently ld does not do the deduplication for SHF_MERGE|SHF_STRINGS >> sections for relocatable files (ld -r), which kernel modules are. See: >> >> https://sourceware.org/ml/binutils/2009-07/msg00291.html > >I know <https://patches-gcc.linaro.org/patch/5858/> :)
That is exactly what we need! :)
>> But, the strings do get deduplicated for vmlinux. Not sure if we can >> find a workaround for modules or if the benefit is significant enough >> if it only for vmlinux. > >I think it's definitely worth if, even if it "only" benefits vmlinux for >now. And I still hope to revisit the --force-section-merge some day, but >it's very far down my priority list.
Yeah, I think it's worth having too.
If you don't have any extra cycles at the moment, and it's far down your priority list, do you mind if I take a look and maybe try to push that patch of yours upstream again? I don't know how successful I'd be, but now since it's especially relevant for namespaces, it's definitely worth looking at again.
Thanks!
Jessica
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