linux-kernel - Re: [PATCH 2/5] x86_32: boot, extract efi_pe_entry from startup

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Date:   Mon, 5 Jun 2017 15:20:14 +0100
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Jiri Slaby <jslaby@...e.cz>
Cc:     mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 2/5] x86_32: boot, extract efi_pe_entry from startup_32

On Wed, 31 May, at 10:12:40AM, Jiri Slaby wrote:
> efi_pe_entry body is somehow squashed into startup_32. In the old days,
> we forced startup_32 to start at offset 0x00 and efi_pe_entry to start
> at 0x10. But this requirement was removed in 99f857db8857 ("x86, build:
> Dynamically find entry points in compressed startup code") long time
> ago.
> 
> The way it is now makes the code less readable and illogical. And given
> we can now safely extract the inlined efi_pe_entry body from
> startup_32 into a separate function, we do so and we separate it to two
> functions as they are marked already: efi_pe_entry + efi32_stub_entry.
> 
> We also annotate the functions appropriatelly by ENTRY+ENDPROC.
> 
> ABI offset is preserved:
>   0000   128 FUNC    GLOBAL DEFAULT    6 startup_32
>   0080    60 FUNC    GLOBAL DEFAULT    6 efi_pe_entry
>   00bc    68 FUNC    GLOBAL DEFAULT    6 efi32_stub_entry
> 
> On the top-level, it looked like:
> 	ENTRY(startup_32)
> 	#ifdef CONFIG_EFI_STUB		; start of inlined
> 		jmp     preferred_addr
> 	ENTRY(efi_pe_entry)
> 		... ; a lot of assembly (efi_pe_entry)
> 	ENTRY(efi32_stub_entry)
> 		... ; a lot of assembly (efi32_stub_entry)
> 		leal    preferred_addr(%eax), %eax
> 		jmp     *%eax
> 	preferred_addr:
> 	#endif				; end of inlined
> 		... ; a lot of assembly (startup_32)
> 	ENDPROC(startup_32)
> 
> And it is converted into:
> 	ENTRY(startup_32)
> 		... ; a lot of assembly (startup_32)
> 	ENDPROC(startup_32)
> 
> 	#ifdef CONFIG_EFI_STUB
> 	ENTRY(efi_pe_entry)
> 		... ; a lot of assembly (efi_pe_entry)
> 	ENDPROC(efi_pe_entry)
> 
> 	ENTRY(efi32_stub_entry)
> 		... ; a lot of assembly (efi32_stub_entry)
> 		leal    startup_32(%eax), %eax
> 		jmp     *%eax
> 	ENDPROC(efi32_stub_entry)
> 	#endif
> 
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: <x86@...nel.org>
> Cc: David Woodhouse <dwmw2@...radead.org>
> Cc: Matt Fleming <matt@...eblueprint.co.uk>
> ---
>  arch/x86/boot/compressed/head_32.S | 129 ++++++++++++++++++-------------------
>  1 file changed, 64 insertions(+), 65 deletions(-)

Reviewed-by: Matt Fleming <matt@...eblueprint.co.uk>