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Date: Sat, 6 Apr 2013 21:45:43 -0400 From: John David Anglin <dave.anglin@...l.net> To: James Bottomley <James.bottomley@...senPartnership.com> CC: Rusty Russell <rusty@...tcorp.com.au>, Sebastian Wankerl <sisewank@....cs.fau.de>, linux-kernel@...r.kernel.org, Philip Kranz <philip.kranz@...glemail.com>, i4passt@...ts.informatik.uni-erlangen.de, linux-parisc@...r.kernel.org, corbet@....net Subject: Re: [PATCH] Add non-zero module sections to sysfs On 6-Apr-13, at 9:22 PM, James Bottomley wrote: > > > John David Anglin <dave.anglin@...l.net> wrote: > >> On 6-Apr-13, at 6:52 AM, James Bottomley wrote: >> >>> On Sat, 2013-04-06 at 15:22 +1030, Rusty Russell wrote: >>>>> The problem is our assumption that section names be unique. This >>>>> assumption is wrong. The ELF spec says (version 1.1 page 1-15): >> "An >>>>> object file may have more than one section with the same name." >>>>> We need >>>>> to fix the kernel not to rely on a bogus assumption ... but we had >> >>>>> no >>>>> idea how to do that in a way that preserved the backwards >>>>> compatibility >>>>> of sections subdirectory. >>>>> >>>>> I admit that 35dead4235e2b67da7275b4122fed37099c2f462 is a hack, >>>>> but now >>>>> the problem has got attention, can we fix it properly? >>>> >>>> Yep. The original patch didn't go through me, or we would have had >> >>>> this >>>> discussion back then... >>>> >>>> The use of section names in sysfs goes back to one Mr. Corbet. Why >> >>>> did >>>> he do it that way? Because gdb's add-symbol-file makes the same >>>> assumption. So if we fixed the sysfs somehow, it still wouldn't be >>>> useful, since there's no way to tell gdb :( >>>> >>>> The real answer don't use -ffunction-sections on modules: probably >>>> not >>>> as important as the rest of the kernel. And the new shiny is >>>> -flto anyway. >>>> >>>> And that leaves us with a PA-RISC specific issue, for which we >> should >>>> move the fix to PA-RISC. >>>> >>>> Thoughts? >>> >>> Well, we don't have much of a choice. Our ELF stub jump on 32 bits >>> is a >>> PCREL17. That means once a module size is over 128k there's a >>> chance we >>> might not be able to link it because the jump is too big for the >>> instruction. IPV6 is one such big module today, but I'm sure there >>> are >>> others. The only way I know to fix this is to allow the linker to >>> insert stubs between functions, so we only fail at linking if a >> single >>> function is >128k big. The way to do this is -ffunction-sections, >>> unless there's something else we could do (all we really need is a >> way >>> to ensure we can insert ELF stubs every 128k). >> >> There is now a config work around for this. See: >> http://www.spinics.net/lists/linux-parisc/msg04521.html > > The longcalls config option only works on pa2 doesn't it? Although > we could just deprecate pa1. No, it works on pa1.1 but the calls are more efficient on pa2. On linux with a flat space, they should be about the same in terms of instruction count. On HP-UX, an additional space register load is needed. For calls within the same space, the be instruction is pretty efficient but we never implemented linker support for it in binutils. If I recall correctly, it works if the call is local to a module but not for global calls. It does work in HP-UX. Dave -- John David Anglin dave.anglin@...l.net -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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