arch/x86/include/asm/checksum_32.h

Source file repositories/reference/linux-study-clean/arch/x86/include/asm/checksum_32.h

File Facts

System
Linux kernel
Corpus path
arch/x86/include/asm/checksum_32.h
Extension
.h
Size
4682 bytes
Lines
187
Domain
Architecture Layer
Bucket
arch/x86
Inferred role
Architecture Layer: implementation source
Status
source implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

#ifndef _ASM_X86_CHECKSUM_32_H
#define _ASM_X86_CHECKSUM_32_H

#include <linux/in6.h>
#include <linux/uaccess.h>

/*
 * computes the checksum of a memory block at buff, length len,
 * and adds in "sum" (32-bit)
 *
 * returns a 32-bit number suitable for feeding into itself
 * or csum_tcpudp_magic
 *
 * this function must be called with even lengths, except
 * for the last fragment, which may be odd
 *
 * it's best to have buff aligned on a 32-bit boundary
 */
asmlinkage __wsum csum_partial(const void *buff, int len, __wsum sum);

/*
 * the same as csum_partial, but copies from src while it
 * checksums, and handles user-space pointer exceptions correctly, when needed.
 *
 * here even more important to align src and dst on a 32-bit (or even
 * better 64-bit) boundary
 */

asmlinkage __wsum csum_partial_copy_generic(const void *src, void *dst, int len);

/*
 *	Note: when you get a NULL pointer exception here this means someone
 *	passed in an incorrect kernel address to one of these functions.
 *
 *	If you use these functions directly please don't forget the
 *	access_ok().
 */
static inline __wsum csum_partial_copy_nocheck(const void *src, void *dst, int len)
{
	return csum_partial_copy_generic(src, dst, len);
}

static inline __wsum csum_and_copy_from_user(const void __user *src,
					     void *dst, int len)
{
	__wsum ret;

	might_sleep();
	if (!user_access_begin(src, len))
		return 0;
	ret = csum_partial_copy_generic((__force void *)src, dst, len);
	user_access_end();

	return ret;
}

/*
 *	This is a version of ip_compute_csum() optimized for IP headers,
 *	which always checksum on 4 octet boundaries.
 *
 *	By Jorge Cwik <jorge@laser.satlink.net>, adapted for linux by
 *	Arnt Gulbrandsen.
 */
static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
{
	unsigned int sum;

	asm volatile("movl (%1), %0	;\n"
		     "subl $4, %2	;\n"
		     "jbe 2f		;\n"
		     "addl 4(%1), %0	;\n"
		     "adcl 8(%1), %0	;\n"
		     "adcl 12(%1), %0;\n"
		     "1:	adcl 16(%1), %0	;\n"
		     "lea 4(%1), %1	;\n"
		     "decl %2	;\n"
		     "jne 1b		;\n"
		     "adcl $0, %0	;\n"
		     "movl %0, %2	;\n"
		     "shrl $16, %0	;\n"
		     "addw %w2, %w0	;\n"
		     "adcl $0, %0	;\n"
		     "notl %0	;\n"
		     "2:		;\n"
	/* Since the input registers which are loaded with iph and ihl
	   are modified, we must also specify them as outputs, or gcc
	   will assume they contain their original values. */
		     : "=r" (sum), "=r" (iph), "=r" (ihl)
		     : "1" (iph), "2" (ihl)
		     : "memory");

Annotation

Implementation Notes