Re: [PATCH] Add non-zero module sections to sysfs

Philip Kranz
2013-04-11T14:11:55Z

On Mon, Apr 08, 2013 at 01:44:45PM +0930, Rusty Russell wrote:
> Philip Kranz <philip.kranz@googlemail.com> writes:
> > Hello.
> >
> > On Fri, Apr 05, 2013 at 12:07:15PM +0200, James Bottomley wrote:
> >> Just so you know: this isn't a parisc specific problem. Gcc produces
> >> duplicate section names under various circumstances, but the one that
> >> bites us is -ffunction-sections. Note that there are proposals to use
> >> -ffunction-sections on all architectures (so we can garbage collect
> >> unused functions) in which case you'll induce the bug identified in
> >> 35dead4235e2b67da7275b4122fed37099c2f462 on every architecture
> >
> > I am not able to produce an object file with duplicate section names
> > using gcc on x86. Even with -ffunction-sections, every section gets a
> > unique name. Is this architecture-specific behaviour of gcc?
>
> Good point. ld -r will collapse them into the same section (since gcc
> produces them they have to have the same section attributes).
>
> You can do it with --unique, but no arch uses that. PARISC has a
> platform-specific toolchain hack which does that for .text sections.
> (Thanks to Alan Modra for that clue...)

Just for clarification, as we are currently preparing a patch set that
depends on this: Would the patch below be an acceptable solution for
this?

Thanks,
Philip

diff --git a/arch/parisc/kernel/module.c b/arch/parisc/kernel/module.c
index 2a625fb..1fd4411 100644
--- a/arch/parisc/kernel/module.c
+++ b/arch/parisc/kernel/module.c
@@ -341,6 +341,11 @@ int module_frob_arch_sections(CONST Elf_Ehdr *hdr,
".PARISC.unwind", 14) == 0)
me->arch.unwind_section = i;

+ /* we produce multiple, empty .text sections, and kallsyms
+ * gets upset. make non-alloc so it doesn't see them. */
+ if (sechdrs[i].sh_size == 0)
+ sechdrs[i].sh_flags &= ~SHF_ALLOC;
+
if (sechdrs[i].sh_type != SHT_RELA)
continue;

diff --git a/kernel/module.c b/kernel/module.c
index 3c2c72d..42e0d5a 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1316,7 +1316,7 @@ resolve_symbol_wait(struct module *mod,
#ifdef CONFIG_KALLSYMS
static inline bool sect_empty(const Elf_Shdr *sect)
{
- return !(sect->sh_flags & SHF_ALLOC) || sect->sh_size == 0;
+ return !(sect->sh_flags & SHF_ALLOC);
}

struct module_sect_attr