Mail Archives: djgpp/2005/11/01/12:48:22
X-Authentication-Warning: | delorie.com: mail set sender to djgpp-bounces using -f
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Date: | Tue, 01 Nov 2005 12:46:01 -0500
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From: | Diego Cueva <dcueva AT todo1 DOT com>
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Subject: | Why the call instruction points 2 bytes before to the real start
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| sub-routine ?
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To: | djgpp AT delorie DOT com
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Message-id: | <003201c5df0c$20f5abe0$2432a8c0@dcueva>
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Reply-To: | djgpp AT delorie DOT com
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Hi:
Please help me with the next issue:
In the next assembler program:
====================== ipl.s ================
.code32
.text
.global start
start:
nop
# Clear screen
call clrscr
# Print Hello world
movw $m1, %si
call impstr
# End
int $0x20
# Clear screen code using assembler
clrscr:
pushw %ax
pushw %bx
pushw %cx
pushw %dx
movb $6, %ah
movb $0, %al
movb $0, %ch
movb $0, %cl
movb $24, %dh
movb $79, %dl
movb $7, %bh
int $0x10
popw %dx
popw %cx
popw %bx
popw %ax
ret
# Putchar using assembler
( ...more code here...)
=============================================
I am using the compiler in this way (to generate a ipl.com file or pure
code machine file):
..\..\tools\as -o ipl.o ipl.s
..\..\tools\ld -m i386go32 -Ttext 0x0100 -s --oformat binary -o ipl.com
ipl.o
When I compile using ".code16" at the top of the code, the ipl.com file
works very fine, that I expected (clear the screen, print "Hello
world\n" and end).
But if I omit, or put explicit ".code32", at the top of the file, the
ipl.com file has the next problem:
1579:0100 90 NOP
1579:0101 E80B00 CALL 010F
1579:0104 0000 ADD [BX+SI],AL
1579:0106 66 DB 66
1579:0107 BE5C01 MOV SI,015C
1579:010A E83400 CALL 0141
1579:010D 0000 ADD [BX+SI],AL
1579:010F CD20 INT 20
NOTE!!!
CALL 010F: Must point to the "clrscr" subroutine, but this subroutine
start at 0111.
CALL 0141: Must point to the "impstr" subroutine, but this subroutine
start at 0143.
Note 2 bytes of displacement in the CALL instruction.
Obviously the ipl.com file compiled with .code32 does not work fine.
010F points directly to INT 0x20 :( :'(
Thanks a lot for your help and time.
Att.
Diego Cueva.
PD: I can accept a RTFM as a response, but say me the section or page.
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