linux-kernel - Re: [tip:x86/urgent] x86/vdso: Discard the __bug

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Message-ID: <CALCETrX8xJQwm=Cp63xSWsmsF1EXB9pPkZ46rX1u49f0oCfxfw@mail.gmail.com>
Date:	Tue, 24 Jun 2014 11:37:08 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/urgent] x86/vdso: Discard the __bug_table section

On Tue, Jun 24, 2014 at 11:26 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 06/24/2014 11:19 AM, Andy Lutomirski wrote:
>>>>
>>>> One of the recent x86/urgent vdso commits causes this build failure:
>>>>
>>>>  Error: too many copied sections (max = 13)
>>>
>>> I can't reproduce this with your config, which suggestes a binutils
>>> issue, which is annoying.  Can you tell me what version of ld you're
>>> using and send me the output of:
>>>
>>> for i in arch/x86/vdso/*.so.dbg; do echo $i; eu-readelf -S $i; done
>>
>> Ping!
>>
>> The current state of this is obviously not so good, but I don't know
>> how to proceed.
>>
>
> We used to have this kind of problems with PHDRs, where ld would guess
> how much space it would need, somehow guess wrong, and fall on its face.
>
> I think we want to actually print the number that we are trying to copy
> in addition to the maximum, and I also noticed the test looks wrong.
> Thus I would like to propose the following patch as a diagnostic:
>
> diff --git a/arch/x86/vdso/vdso2c.h b/arch/x86/vdso/vdso2c.h
> index f42e2ddc663d..94158e100f26 100644
> --- a/arch/x86/vdso/vdso2c.h
> +++ b/arch/x86/vdso/vdso2c.h
> @@ -99,8 +99,9 @@ static void BITSFUNC(copy_section)(struct
> BITSFUNC(fake_sections) *out,
>         if (!copy)
>                 return;
>
> -       if (out->count >= out->max_count)
> -               fail("too many copied sections (max = %d)\n",
> out->max_count);
> +       if (out->count > out->max_count)
> +               fail("too many copied sections (max = %d, need = %d)\n",
> +                    out->max_count, out->count);
>

I think the old test was correct: we haven't incremented count yet
(it's a couple lines below), so count is the zero-based index to which
we're writing.

I thought of doing the need = %d thing, but I think that the output is
a foregone conclusion: count == max_count + 1 when this fails.  A list
of all the section names would be more interesting, but eu-readelf -S
will tell is that.

--Andy
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