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

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Date:	Thu, 11 Apr 2013 16:11:55 +0200
From:	Philip Kranz <philip.kranz@...glemail.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Philip Kranz <philip.kranz@...glemail.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Sebastian Wankerl <sisewank@....cs.fau.de>,
	linux-kernel@...r.kernel.org,
	i4passt@...ts.informatik.uni-erlangen.de,
	linux-parisc@...r.kernel.org
Subject: Re: [PATCH] Add non-zero module sections to sysfs

On Mon, Apr 08, 2013 at 01:44:45PM +0930, Rusty Russell wrote:
> Philip Kranz <philip.kranz@...glemail.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

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