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From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
To: Sam James <sam@gentoo.org>
Cc: Adrian Ratiu <adrian.ratiu@collabora.com>, libc-alpha@sourceware.org
Subject: Re: [PATCH] arm: Remove unused ldr _dl_start_user
Date: Mon, 5 Feb 2024 15:09:00 -0300	[thread overview]
Message-ID: <53d1dad6-4506-4ff9-9d1e-0c4125ad8726@linaro.org> (raw)
In-Reply-To: <87bk8ual6f.fsf@gentoo.org>



On 05/02/24 14:13, Sam James wrote:
> 
> Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:
> 
>> 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
>> initialize it and thus trigger an invalid memory access.
> 
> Tag the bug?
> 
> Also, I feel like the title perhaps makes the change sound more cosmetic
> than it is.

Right, I will change to 'arm: Remove wrong ldr _dl_start_user (BZ 31339)'

> 
>>
>> Checked on arm-linux-gnu.
>>
>> 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\
> 

  reply	other threads:[~2024-02-05 18:09 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-02-05 16:18 Adhemerval Zanella
2024-02-05 17:06 ` Szabolcs Nagy
2024-02-05 17:08   ` Adhemerval Zanella Netto
2024-02-05 17:13 ` Sam James
2024-02-05 18:09   ` Adhemerval Zanella Netto [this message]
2024-02-05 18:19     ` Sam James

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