On Mon, Aug 22, 2016 at 11:59:46AM +0200, Vegard Nossum wrote: > On 19 August 2016 at 23:41, <mcgrof@xxxxxxxxxx> wrote: > > From: "Luis R. Rodriguez" <mcgrof@xxxxxxxxxx> > > > > The original v3 series for linker tables made reference only to > > an external repository userspace sandbox application, however > > Boris noted it'd be difficult ot keep this in sync with the > > kernel so advised to consider integrate with the kernel. I've > > taken steps in this direction. > [...] > > Please let me know if there are any issue or questions. > > +#define __VMLINUX_SYMBOL(x) x > > +#define VMLINUX_SYMBOL(x) __VMLINUX_SYMBOL(x) > > +#define LINUX_SECTION_START(name) VMLINUX_SYMBOL(name) > > +#define DECLARE_LINUX_SECTION(type, name) \ > + extern type VMLINUX_SYMBOL(name)[], \ > + VMLINUX_SYMBOL(name##__end)[] > > +#define DECLARE_LINKTABLE(type, name) \ > + DECLARE_LINUX_SECTION(type, name) > > +#define LINKTABLE_FOR_EACH(pointer, tbl) \ > + for (pointer = LINUX_SECTION_START(tbl); \ > + pointer < LINUX_SECTION_END(tbl); \ > + pointer++) > > I think this is subject to getting optimised out by newer gccs, since > it sees the START(tbl) and END(tbl) symbols as two completely > different arrays. See the short discussion here: > > https://lkml.org/lkml/2016/6/26/73 (the first attempt is wrong, so > don't look at that) > > It is possible that < is different from != and always does the right > thing, but I haven't checked. > > I have a WIP branch that converts most of the existing tables in the > kernel to use the external_array() macro which makes gcc throw away > any knowledge it had about a pointer being part of an array. Was there no compiler option to disable the optimization ? Please do Cc me on your patches, either way we can coordinate changes depending on which series gets merged. If your external_array() change lands upstream first I'll see it on linux-next shortly can rebase and adjust code then as that is what I base my patches on. Do we know if there exceptions to the optimization issue for this and if so what patterns follow ? We can test with simple userspace code if this will be an issue with gcc 7 by trying the demo in tools/linker-tables/ using this git tree and branch 20160819-linker-table-v4 : https://git.kernel.org/cgit/linux/kernel/git/mcgrof/linux-next.git/log/?h=20160819-linker-table-v4 Luis -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
