Re: [PATCH] arm: Remove unused ldr _dl_start_user

[Sam James <sam@gentoo.org>]

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.

>
> 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\