linux-kernel - Re: [PATCH 8/9] x86, efi: EFI boot stub support

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Date:	Thu, 11 Aug 2011 11:09:35 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Mike Waychison <mikew@...gle.com>,
	Matthew Garrett <mjg@...hat.com>
Subject: Re: [PATCH 8/9] x86, efi: EFI boot stub support

Matt Fleming <matt@...sole-pimps.org> writes:
> +
> +	status = efi_call_phys3(sys_table->boottime->allocate_pool,
> +				EFI_LOADER_DATA, sizeof(*idt),
> +				(void **)&idt);
> +	if (status != EFI_SUCCESS)
> +		goto fail;
> +
> +	idt->size = 0;
> +	idt->address = 0;
> +
> +	status = make_boot_params(boot_params, image, handle);
> +	if (status != EFI_SUCCESS)
> +		goto fail;
> +
> +	memset((char *)gdt->address, 0x0, gdt->size);
> +	desc = (u64 *)gdt->address;
> +
> +	/*
> +	 * 4Gb - (0x100000*0x1000 = 4Gb)
> +	 * base address=0
> +	 * code read/exec
> +	 * granularity=4096, 386 (+5th nibble of limit)
> +	 */
> +	desc[2] = 0x00cf9a000000ffff;
> +
> +	/*
> +	 * 4Gb - (0x100000*0x1000 = 4Gb)
> +	 * base address=0
> +	 * data read/write
> +	 * granularity=4096, 386 (+5th nibble of limit)
> +	 */
> +	desc[3] = 0x00cf92000000ffff;
> +
> +	/* Task segment value */
> +	desc[4] = 0x0080890000000000;

The code would benefit from more variables/defines and less magic numbers.

I assume this is all virtual, otherwise it would be really scary.

> +	asm volatile ("lidt %0" :: "m" (*idt));
> +	asm volatile ("lgdt %0" :: "m" (*gdt));
> +
> +	asm volatile("cli");

::: "memory" to avoid moving

> +
> +	return boot_params;
> +fail:
> +	return NULL;

Does the caller actually something useful here for NULL? Better to have
messages when any of this fails.

> +int memcmp(const void *s1, const void *s2, size_t len)
> +{
> +	u8 diff;
> +	asm("repe; cmpsb; setnz %0"
> +	    : "=qm" (diff), "+D" (s1), "+S" (s2), "+c" (len));

This doesn't describe to gcc that the inline assembler 
reads s1 and s2. At the minimum add a memory clobber.

> +
> +/**
> + * strlen - Find the length of a string
> + * @s: The string to be sized
> + */
> +size_t strlen(const char *s)
> +{
> +	const char *sc;
> +
> +	for (sc = s; *sc != '\0'; ++sc)
> +		/* nothing */;
> +	return sc - s;
> +}

Why not just link in/#include lib/string.c ? 


-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only
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