Author: cperciva
Date: Thu Oct 8 15:38:34 2015
New Revision: 289031
URL: https://svnweb.freebsd.org/changeset/base/289031
Log:
Change gptldr from relocating 0xfff1 bytes of boot2 to relocating 0x20000
bytes of boot2. Since we're in 16-bit mode, we can't copy all 128kB at
once; instead we loop four times and copy 32 kB each time.
This change was made necessary by an upcoming increase in the size of the
boot2 binary; should it increase further, the COPY_BLKS value can be
adjusted without anyone needing to remember 8086 assembly language again.
Requested by: allanjude
Tested by: allanjude
MFC after: 1 week
Modified:
head/sys/boot/i386/gptboot/gptldr.S
Modified: head/sys/boot/i386/gptboot/gptldr.S
==============================================================================
--- head/sys/boot/i386/gptboot/gptldr.S Thu Oct 8 15:13:57 2015
(r289030)
+++ head/sys/boot/i386/gptboot/gptldr.S Thu Oct 8 15:38:34 2015
(r289031)
@@ -45,6 +45,10 @@
/* Misc. Constants */
.set SIZ_PAG,0x1000 # Page size
.set SIZ_SEC,0x200 # Sector size
+ .set COPY_BLKS,0x4 # Number of blocks
+ # to copy for boot2
+ .set COPY_BLK_SZ,0x8000 # Copy in 32k blocks; must be
+ # a multiple of 16 bytes
.globl start
.code16
@@ -68,26 +72,39 @@ start: xor %cx,%cx # Zero
* its header to find boot2. We need to copy boot2 to MEM_USR and BTX
* to MEM_BTX. Since those might overlap, we have to copy boot2
* backwards first and then copy BTX. We aren't sure exactly how long
- * boot2 is, but we assume it can't be longer than 64k, so we just always
- * copy 64k.
+ * boot2 is, but it's currently under 128kB so we'll copy 4 blocks of 32kB
+ * each; this can be adjusted via COPY_BLK and COPY_BLK_SZ above.
*/
mov $end,%bx # BTX
mov 0xa(%bx),%si # Get BTX length and set
add %bx,%si # %si to start of boot2
- mov %si,%ax # Align %ds:%si on a
- shr $4,%ax # paragraph boundary
- and $0xf,%si # with the smallest
- mov %ax,%ds # possible %si
- add $(64 * 1024 - 16),%si
- mov $MEM_USR/16,%ax # Point %es:%di at end of
- mov $(64 * 1024 - 16),%di # largest boot2 range
+ dec %si # Set %ds:%si to point at the
+ mov %si,%ax # last byte we want to copy
+ shr $4,%ax # from boot2, with %si made as
+ add $(COPY_BLKS*COPY_BLK_SZ/16),%ax # small as possible.
+ and $0xf,%si #
+ mov %ax,%ds #
+ mov $MEM_USR/16,%ax # Set %es:(-1) to point at
+ add $(COPY_BLKS*COPY_BLK_SZ/16),%ax # the last byte we
+ mov %ax,%es # want to copy boot2 into.
+ mov $COPY_BLKS,%bx # Copy COPY_BLKS 32k blocks
+copyloop:
+ add $COPY_BLK_SZ,%si # Adjust %ds:%si to point at
+ mov %ds,%ax # the end of the next 32k to
+ sub $COPY_BLK_SZ/16,%ax # copy from boot2
+ mov %ax,%ds
+ mov $COPY_BLK_SZ-1,%di # Adjust %es:%di to point at
+ mov %es,%ax # the end of the next 32k into
+ sub $COPY_BLK_SZ/16,%ax # which we want boot2 copied
mov %ax,%es
+ mov $COPY_BLK_SZ,%cx # Copy 32k
std
- mov %di,%cx # Copy 64k - paragraph + 1
- inc %cx # bytes
rep movsb
+ dec %bx
+ jnz copyloop
mov %cx,%ds # Reset %ds and %es
mov %cx,%es
+ mov $end,%bx # BTX
mov 0xa(%bx),%cx # Get BTX length and set
mov %bx,%si # %si to end of BTX
mov $MEM_BTX,%di # %di -> end of BTX at
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