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

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Message-ID: <87vc81lj7x.fsf@rustcorp.com.au>
Date:	Fri, 05 Apr 2013 14:30:50 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Sebastian Wankerl <sisewank@....cs.fau.de>
Cc:	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
Subject: Re: [PATCH] Add non-zero module sections to sysfs

Sebastian Wankerl <sisewank@....cs.fau.de> writes:
> On 04/04/13 03:00, Rusty Russell wrote:
>> Sebastian Wankerl <sisewank@....cs.fau.de> writes:
>>> Add non-zero module sections to sysfs on architectures unequal to PARISC.
>>> KGDB needs all module sections for proper module debugging. Therefore, commit 
>>> 35dead4235e2b67da7275b4122fed37099c2f462 is revoked except for PARISC
>>> architecture.
>> #ifdef CONFIG_PARISC in the middle of kernel/module.c is super-ugly, and
>> wrong.
>
> I don't see why this is wrong. It used to load all sections to sysfs
> until the patch mentioned. Actually, it is the PARISC build chain which
> is broken.

Exactly.  Don't workaround it here, revert it and put the
duplicate-section-name fixup in parisc where it belongs.

Assuming parisc still produces these dup sections: that patch is 4 years
old now.

Untested:

diff --git a/arch/parisc/kernel/module.c b/arch/parisc/kernel/module.c
index 2a625fb..28d32a2 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;
 
>> My preference would be to fix kgdb.  If the section is empty, what need
>> does it have to examine it?
>
> GDB needs to know all sections of the binary and its addresses.

Why?  Does something refer to this empty section?  Why has noone noticed
this since 2009?

> It is generally useful to be able to check up all sections of the binary
> regardless if they are empty or not so one can see the binary's
> structure.

A zero-length section doesn't change the binary's structure.  You don't
see non-SHF_ALLOC sections either.

Cheers,
Rusty.
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