On June 15, 2014 10:40:03 AM PDT, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >On Sun, Jun 15, 2014 at 10:05 AM, H. Peter Anvin <hpa@xxxxxxxxx> wrote: >> On 06/15/2014 07:35 AM, Rich Felker wrote: >>> >>> Arguably, it was a mistake for the kernel to expose a virtual ELF to >>> begin with, and it should just have exposed a "lookup function by >>> name" operation to begin with. Yes this can be done in userspace, >but >>> I see it more as a matter of "fixing a broken API design". >>> >> >> What the fsck are you smoking? There is immense value in providing a >> stable and very well-defined data structure, which also happens to be >> what dynamic linkers already want to consume. Providing a helper for >> crippled libc applications has potential value. Shaving a few >hundred >> bytes off static applications is a very weak argument, simply because >it >> is such a small fraction of the enormous cost of a static >application, >> and static applications are problematic in a number of other ways, >> especially the lack of ability to fix bugs. >> >> Treating the kernel as an ersatz dynamic library for "static" >> applications is kind of silly -- after all, why not provide an entire >> libc in the vdso? I have actually seen people advocate for doing >that. > >To be clear, I have no desire whatsoever to give the vdso an actual >ELF parser or anything else that userspace should be providing itself. >I think that a special-purpose vdso parser in the vdso makes some >sense, though, since userspace might otherwise provide one for the >sole purpose of parsing the vdso. > >And there's plenty of reasons that having the vdso be an ELF image is >useful. For one thing, gdb can take advantage of it. For another, >CRIU is parsing it for a rather different reason, and something like >__vdso_findsym won't fill that need. > >Also, given the general lack of a comprehensible specification of what >the GNU flavor of the ELF format actually is [1], there's something to >be said for reducing the proliferation of ELF parsers. glibc and >binutils are quite unlikely to become incompatible with each other, >but I sincerely doubt that anyone from binutils land is likely to >review (and maintain!) my ELF parser, Go's, or a hypothetical future >ELF parser from any of the other glibc-less things. If those things >use one that's in the kernel, then it's easy for the kernel to >guarantee that each vdso image can successfully parse itself. > >[1] The only comprehensible description of the GNU hash extension that >I could find is on Oracle's blog (!) > Curious about this blog. We do have a GNU hash implementation in Syslinux, too, for another reference. -- Sent from my mobile phone. Please pardon brevity and lack of formatting. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
