linux-kernel - Re: Problems with commit 'kallsyms: add support for relative offsets in kallsyms address table' (in mmotm)

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Message-Id: <53850CA2-9839-4402-AE9E-238F0CD2BB88@linaro.org>
Date:	Sun, 24 Jan 2016 20:01:17 +0100
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Problems with commit 'kallsyms: add support for relative offsets in kallsyms address table' (in mmotm)



> On 24 jan. 2016, at 19:01, Guenter Roeck <linux@...ck-us.net> wrote:
> 
> On 01/24/2016 09:20 AM, Ard Biesheuvel wrote:
> [ ... ]
>>>> OK, there's an additional issue in my latest version: the
>>>> kallsyms_relative_base value itself is not relocated.
>>>> 
>>>> If you have more time to burn on this, could you try the following on
>>>> top? (If not, that is also fine, I will look into it myself on Monday)
>>>> 
>>>> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
>>>> index 5ab13394dfd9..0f43f0751d47 100644
>>>> --- a/scripts/kallsyms.c
>>>> +++ b/scripts/kallsyms.c
>>>> @@ -137,8 +137,10 @@ static int read_symbol(FILE *in, struct sym_entry *s)
>>>>                 sym++;
>>>> 
>>>>         /* Ignore most absolute/undefined (?) symbols. */
>>>> -       if (strcmp(sym, "_text") == 0)
>>>> +       if (strcmp(sym, "_text") == 0) {
>>>>                 _text = s->addr;
>>>> +               stype = 'T';
>>>> +       }
>>>>         else if (check_symbol_range(sym, s->addr, text_ranges,
>>>>                                     ARRAY_SIZE(text_ranges)) == 0)
>>>>                 /* nothing to do */;
>>>> @@ -406,7 +408,7 @@ static void write_src(void)
>>>> 
>>>>         if (base_relative) {
>>>>                 output_label("kallsyms_relative_base");
>>>> -               printf("\tPTR\t%#llx\n", relative_base);
>>>> +               printf("\tPTR\t_text - %#llx\n", _text - relative_base);
>>>>                 printf("\n");
>>>>         }
>>> 
>>> Does not help.
>>> 
>> 
>> For x86? Or none of them?
>> 
> 
> I tested sparc32 and x86_64/nosmp. Doesn't help for any of them.
> sparc32 has the following absolute symbols.
> 
> f035a420 A _etext
> f03d9000 A _sdata
> f03de8c4 A jiffies
> f03f8860 A _edata
> f03fc000 A __init_begin
> f041bdc8 A __init_text_end
> f0423000 A __bss_start
> f0423000 A __init_end
> f044457d A __bss_stop
> f044457d A _end
> 

Any clue why these don't get dropped? Am I missing something? Afaict A symbols get dropped unless they are whitelisted (i.e., the few ia64 ones)

> This results in:
> 
> kallsyms failure: absolute symbol value 0xf035a420 out of range in relative mode
> 
> This is with binutils 2.22. I didn't test with binutils 2.25 for sparc, or re-test mips.
> 
> 
> Looks like I'll need to add more test cases with binutils 2.22 vs. 2.25 for various
> architectures, as well as more SMP vs. !SMP builds.
> 

Thanks once again