linux-kernel - Re: [PATCH 1/2] x86/boot/compressed/64: Set up GOT for paging_prepare() and cleanup

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Date:   Sun, 13 May 2018 20:55:46 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
cc:     Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86/boot/compressed/64: Set up GOT for paging_prepare()
 and cleanup_trampoline()

On Thu, 10 May 2018, Kirill A. Shutemov wrote:

> +	/*
> +	 * paging_prepare() and cleanup_trampoline() below can have GOT
> +	 * references. Adjust the table with address we are running at.
> +	 */
> +
> +	/* The GOP was not adjusted before */

GOP == EFI speak for Graphics Output Protocol. What the heck? 

> +	xorq	%rax, %rax

And this clearing of RAX is related to this because? Sure you need it for
adjust_got() but adding a comment to that is too much asked for, right?

> +	/* Calculate the address the binary is loaded at. */
> +	call	1f
> +1:	popq	%rdi
> +	subq	$1b, %rdi
> +
> +	call	adjust_gop
> +
>  	/*
>  	 * At this point we are in long mode with 4-level paging enabled,
>  	 * but we might want to enable 5-level paging or vice versa.
> @@ -381,6 +396,24 @@ trampoline_return:
>  	pushq	$0
>  	popfq
>  
> +	/*
> +	 * Previously we've adjusted the GOT with address the binary was
> +	 * loaded at. Now we need to re-adjust for relocation address.
> +	 */

Breaking up those comments makes it more readable, right?

> +	/*
> +	 * Calculate the address the binary is loaded at.
> +	 * This address was used to adjust the table before and we need to
> +	 * undo the change.
> +	 */
> +	call	1f
> +1:	popq	%rax
> +	subq	$1b, %rax
> +
> +	/* The new adjustment is relocation address */

  is the relocation address

> +	movq	%rbx, %rdi
> +	call	adjust_gop
> +
>  /*
>   * Copy the compressed kernel to the end of our buffer
>   * where decompression in place becomes safe.
> @@ -481,19 +514,6 @@ relocated:
>  	shrq	$3, %rcx
>  	rep	stosq
>  
> -/*
> - * Adjust our own GOT
> - */
> -	leaq	_got(%rip), %rdx
> -	leaq	_egot(%rip), %rcx
> -1:
> -	cmpq	%rcx, %rdx
> -	jae	2f
> -	addq	%rbx, (%rdx)
> -	addq	$8, %rdx
> -	jmp	1b
> -2:
> -	
>  /*
>   * Do the extraction, and jump to the new kernel..
>   */
> @@ -512,6 +532,26 @@ relocated:
>   */
>  	jmp	*%rax
>  
> +/*
> + * Adjust global offest table

offest? 

> + *
> + * RAX is previous adjustment of the table to undo (0 if it's the first time we touch GOP).

  is the previous

And there is no reason to make that line overly long.

> + * RDI is the new adjustment to apply.
> + */
> +adjust_gop:
> +	/* Walk through the GOT adding the address to the entries */
> +	leaq	_got(%rip), %rdx
> +	leaq	_egot(%rip), %rcx
> +1:
> +	cmpq	%rcx, %rdx
> +	jae	2f
> +	subq	%rax, (%rdx)	/* Undo previous adjustment */
> +	addq	%rdi, (%rdx)	/* Apply the new adjustment */
> +	addq	$8, %rdx
> +	jmp	1b
> +2:
> +	ret

I'm really tired of your carelessness. The amount of half baken stuff you
submit is way above the tolerance level by now. I asked you several times
to be more careful, but you simply do not care at all. Get your act
together finally.

Thanks,

	tglx