Re: [PATCH] arm: Remove unused ldr _dl_start_user

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 05/02/24 14:06, Szabolcs Nagy wrote:
> The 02/05/2024 16:18, Adhemerval Zanella wrote:
>> The commit 49d877a80b29d3002887b084eec6676d9f5fec18 (arm: Remove
>> _dl_skip_args usage) removed the _SKIP_ARGS literal, which was
>> previously loader to r4 on loader _start.  However, the cleanup did not
>> remove the following 'ldr r4, [sl, r4]' on _dl_start_user, used to check
>> to skip the arguments after ld self-relocations.
>>
>> In my testing, the kernel initially set r4 to 0, which makes the
>> ldr instruction just read the _GLOBAL_OFFSET_TABLE_.  However, since r4
>> is a caller-saved register; a different runtime might not zero
>        ^^^^^^
> 
> it's callee-saved (preserved by calls)

Yeah, I meant calee-saved indeed.  I will fix the commit message.

> 
>> initialize it and thus trigger an invalid memory access.
>>
>> Checked on arm-linux-gnu.
> 
> patch looks good.
> 
> Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
> 
>>
>> Reported-by: Adrian Ratiu <adrian.ratiu@collabora.com>
>> ---
>>  sysdeps/arm/dl-machine.h | 1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/sysdeps/arm/dl-machine.h b/sysdeps/arm/dl-machine.h
>> index b857bbc868..dd1a0f6b6e 100644
>> --- a/sysdeps/arm/dl-machine.h
>> +++ b/sysdeps/arm/dl-machine.h
>> @@ -139,7 +139,6 @@ _start:\n\
>>  _dl_start_user:\n\
>>  	adr	r6, .L_GET_GOT\n\
>>  	add	sl, sl, r6\n\
>> -	ldr	r4, [sl, r4]\n\
>>  	@ save the entry point in another register\n\
>>  	mov	r6, r0\n\
>>  	@ get the original arg count\n\
>> -- 
>> 2.34.1
>>