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

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Message-ID: <56A51182.9040105@roeck-us.net>
Date:	Sun, 24 Jan 2016 10:01:38 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
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 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

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.

Guenter