linux-kernel - Re: [PATCH 05/10] kbuild: sort the list of symbols exported by the kernel (_

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Message-Id: <20091125164033.655810b7.akpm@linux-foundation.org>
Date:	Wed, 25 Nov 2009 16:40:33 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alan Jenkins <alan-jenkins@...fmail.co.uk>
Cc:	greg@...ah.com, linux-kbuild@...r.kernel.org, carmelo73@...il.com,
	linux-kernel@...r.kernel.org, rusty@...tcorp.com.au,
	Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH 05/10] kbuild: sort the list of symbols exported by the
 kernel (__ksymtab)

On Tue,  3 Nov 2009 10:06:17 +0000
Alan Jenkins <alan-jenkins@...fmail.co.uk> wrote:

> modpost of vmlinux.o now extracts the ksymtab sections and outputs
> sorted versions of them as .tmp_exports-asm.S.  These sorted sections
> are linked into vmlinux and the original unsorted sections are
> discarded.
> 
> This will allow modules to be loaded faster, resolving symbols using
> binary search, without any increase in the memory needed for the
> symbol tables.
> 
> This does not affect the building of modules, so hopefully it won't
> affect compile times too much.
> 
> Minimally tested on ARM under QEMU emulator.
> Build tested on blackfin; output of "size -A" unchanged.

I'm getting a segfault from write_exports().  

(gdb) bt
#0  0x0000003e5f075510 in strlen () from /lib64/libc.so.6
#1  0x0000003e5f045cb8 in vfprintf () from /lib64/libc.so.6
#2  0x0000003e5f06683a in vsnprintf () from /lib64/libc.so.6
#3  0x0000000000401897 in buf_printf (buf=0x7fff5514f5e0, 
    fmt=0x7fff5514f4e0 "0x%02x ") at scripts/mod/modpost.c:1692
#4  0x00000000004042c8 in main (argc=1024, argv=0x7fff5514f5e0)
    at scripts/mod/modpost.c:2063
(gdb) f 4
#4  0x00000000004042c8 in main (argc=1024, argv=0x7fff5514f5e0)
    at scripts/mod/modpost.c:2063
2063                    buf_printf(&buf, "__EXPORT_%s_SYMBOL(%s,"
(gdb) p sym
$1 = (struct symbol *) 0x65c9f0
(gdb) p *sym
$2 = {next = 0x64c3a0, module = 0x610010, crc = 4077789248, crc_valid = 1, 
  weak = 0, vmlinux = 0, kernel = 0, preloaded = 0, function = 1, 
  export = export_unknown, name = 0x65ca10 "simple_prepare_write"}
(gdb) p sym->export
$3 = export_unknown
(gdb) p/d sym->export
$4 = 5

but section_names[] (which could be static in write_exports() btw) has
only five entries.
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