Re: mmotm 2009-01-28-02-17 uploaded (i386 build errors: cpusets &kexec)

From: Andrew Morton
Date: Thu Jan 29 2009 - 14:50:33 EST


On Thu, 29 Jan 2009 14:27:34 -0500
Neil Horman <nhorman@xxxxxxxxxxxxx> wrote:

> On Thu, Jan 29, 2009 at 10:01:57AM -0800, Andrew Morton wrote:
> > On Thu, 29 Jan 2009 07:09:35 -0500 Neil Horman <nhorman@xxxxxxxxxxxxx> wrote:
> >
> > > > > So does that.
> > > > >
> > > > > --- a/kernel/printk.c~kexec-add-dmesg-log-symbols-to-proc-vmcoreinfo-lists-fix-fix
> > > > > +++ a/kernel/printk.c
> > > > > @@ -137,11 +137,13 @@ static char *log_buf = __log_buf;
> > > > > static int log_buf_len = __LOG_BUF_LEN;
> > > > > static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
> > > > >
> > > > > +#ifdef CONFIG_KEXEC
> > > > > void log_buf_kexec_setup(void)
> > > > > {
> > > > > VMCOREINFO_SYMBOL(log_buf);
> > > > > VMCOREINFO_SYMBOL(log_end);
> > > > > }
> > > > > +#endif
> > > > >
> > > > > static int __init log_buf_len_setup(char *str)
> > > > > {
> > > > > _
> > > >
> > > > Weird, I thought I checked that just now. In any case this email
> > > > was already in my inbox. In any case, I can now produce the problem,
> > > > and this patch resolves it.
> > > >
> > >
> > > Sorry, i didn't think to check on conditions when CONFIG_KEXEC wasn't set. I
> > > assumed we had a stub for all the VMCOREINFO defines. Why don't we fix it in
> > > that manner? I mean we have serveral arch specific additions to vmcoreinfo, all
> > > of which apparently must be ifdefd for this to work. Why not just fix it in
> > > conditional definition?
> >
> > I didn't do that because then we'd have an empty function log_buf_kexec_setup()
> > floating about in every vmlinux.
> >
> > Hardly a big issue, but a bit regrettable.
> >
> Won't the compiler just eliminate that symbol during final link, given that its
> not an exported symbol?

I don't think it's that smart.

akpm:/home/akpm> cat t.c

void foo(void)
{
}

main()
{
}
akpm:/home/akpm> gcc -O2 t.c
akpm:/home/akpm> nm a.out|grep foo
08048300 T foo

With -ffunction-sections or other fancy options, maybe. And it'll be
version-dependent.

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