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linux-next/arch/i386/boot/edd.c
H. Peter Anvin b015124e56 [x86 setup] Volatilize asm() statements
asm() statements need to be volatile when:

a. They have side effects (other than value returned).
b. When the value returned can vary over time.
c. When they have ordering constraints that cannot be expressed to gcc.

In particular, the keyboard and timer reads were violating constraint (b),
which resulted in the keyboard/timeout poll getting
loop-invariant-removed when compiling with gcc 4.2.0.

Thanks to an anonymous bug reporter for pointing this out.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
2007-08-23 13:03:25 -07:00

168 lines
3.8 KiB
C

/* -*- linux-c -*- ------------------------------------------------------- *
*
* Copyright (C) 1991, 1992 Linus Torvalds
* Copyright 2007 rPath, Inc. - All Rights Reserved
*
* This file is part of the Linux kernel, and is made available under
* the terms of the GNU General Public License version 2.
*
* ----------------------------------------------------------------------- */
/*
* arch/i386/boot/edd.c
*
* Get EDD BIOS disk information
*/
#include "boot.h"
#include <linux/edd.h>
#if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
/*
* Read the MBR (first sector) from a specific device.
*/
static int read_mbr(u8 devno, void *buf)
{
u16 ax, bx, cx, dx;
ax = 0x0201; /* Legacy Read, one sector */
cx = 0x0001; /* Sector 0-0-1 */
dx = devno;
bx = (size_t)buf;
asm volatile("pushfl; stc; int $0x13; setc %%al; popfl"
: "+a" (ax), "+c" (cx), "+d" (dx), "+b" (bx)
: : "esi", "edi", "memory");
return -(u8)ax; /* 0 or -1 */
}
static u32 read_mbr_sig(u8 devno, struct edd_info *ei, u32 *mbrsig)
{
int sector_size;
char *mbrbuf_ptr, *mbrbuf_end;
u32 buf_base, mbr_base;
extern char _end[];
sector_size = ei->params.bytes_per_sector;
if (!sector_size)
sector_size = 512; /* Best available guess */
/* Produce a naturally aligned buffer on the heap */
buf_base = (ds() << 4) + (u32)&_end;
mbr_base = (buf_base+sector_size-1) & ~(sector_size-1);
mbrbuf_ptr = _end + (mbr_base-buf_base);
mbrbuf_end = mbrbuf_ptr + sector_size;
/* Make sure we actually have space on the heap... */
if (!(boot_params.hdr.loadflags & CAN_USE_HEAP))
return -1;
if (mbrbuf_end > (char *)(size_t)boot_params.hdr.heap_end_ptr)
return -1;
if (read_mbr(devno, mbrbuf_ptr))
return -1;
*mbrsig = *(u32 *)&mbrbuf_ptr[EDD_MBR_SIG_OFFSET];
return 0;
}
static int get_edd_info(u8 devno, struct edd_info *ei)
{
u16 ax, bx, cx, dx, di;
memset(ei, 0, sizeof *ei);
/* Check Extensions Present */
ax = 0x4100;
bx = EDDMAGIC1;
dx = devno;
asm("pushfl; stc; int $0x13; setc %%al; popfl"
: "+a" (ax), "+b" (bx), "=c" (cx), "+d" (dx)
: : "esi", "edi");
if ((u8)ax)
return -1; /* No extended information */
if (bx != EDDMAGIC2)
return -1;
ei->device = devno;
ei->version = ax >> 8; /* EDD version number */
ei->interface_support = cx; /* EDD functionality subsets */
/* Extended Get Device Parameters */
ei->params.length = sizeof(ei->params);
ax = 0x4800;
dx = devno;
asm("pushfl; int $0x13; popfl"
: "+a" (ax), "+d" (dx), "=m" (ei->params)
: "S" (&ei->params)
: "ebx", "ecx", "edi");
/* Get legacy CHS parameters */
/* Ralf Brown recommends setting ES:DI to 0:0 */
ax = 0x0800;
dx = devno;
di = 0;
asm("pushw %%es; "
"movw %%di,%%es; "
"pushfl; stc; int $0x13; setc %%al; popfl; "
"popw %%es"
: "+a" (ax), "=b" (bx), "=c" (cx), "+d" (dx), "+D" (di)
: : "esi");
if ((u8)ax == 0) {
ei->legacy_max_cylinder = (cx >> 8) + ((cx & 0xc0) << 2);
ei->legacy_max_head = dx >> 8;
ei->legacy_sectors_per_track = cx & 0x3f;
}
return 0;
}
void query_edd(void)
{
char eddarg[8];
int do_mbr = 1;
int do_edd = 1;
int devno;
struct edd_info ei, *edp;
u32 *mbrptr;
if (cmdline_find_option("edd", eddarg, sizeof eddarg) > 0) {
if (!strcmp(eddarg, "skipmbr") || !strcmp(eddarg, "skip"))
do_mbr = 0;
else if (!strcmp(eddarg, "off"))
do_edd = 0;
}
edp = boot_params.eddbuf;
mbrptr = boot_params.edd_mbr_sig_buffer;
if (!do_edd)
return;
for (devno = 0x80; devno < 0x80+EDD_MBR_SIG_MAX; devno++) {
/*
* Scan the BIOS-supported hard disks and query EDD
* information...
*/
get_edd_info(devno, &ei);
if (boot_params.eddbuf_entries < EDDMAXNR) {
memcpy(edp, &ei, sizeof ei);
edp++;
boot_params.eddbuf_entries++;
}
if (do_mbr && !read_mbr_sig(devno, &ei, mbrptr++))
boot_params.edd_mbr_sig_buf_entries = devno-0x80+1;
}
}
#endif