Hi,
2- The same code as seen from ndisasm:
000068DA A00080 mov al,[0x8000]
000068DD 04F5 add al,0xf5
000068DF 0002 add [bp+si],al
000068E1 C8008015 enter 0x8000,0x15
000068E5 0E push cs
000068E6 0106C800 add [0xc8],ax
000068EA 80100E adc byte [bx+si],0xe
000068ED 0105 add [di],ax
000068EF C800800B enter 0x8000,0xb
000068F3 0E push cs
000068F4 0104 add [si],ax
000068F6 C8008006 enter 0x8000,0x6
000068FA 0E push cs
000068FB 0102 add [bp+si],ax
000068FD E80080 call 0xe900 <<<<<!!!HERE AGAIN
This is probably data -- either font data or VGA register tables. Can
you trace backwards any more and figure out how you got to 68DA?
You are right. I have found that the problem was on a JMP SHORT which
was incorrectly landing in that part of the VGA BIOS. The relative
displacement was negative (was 0xBA), but the JMP was considering it to
be a jump to [PC]+0xBA rather than applying the signed arithmetic.
Setting GCC "-fsigned-char " switch made the signed displacemnt
correctly applied....and solved the problem. I didn't know that the
"char" type was unsigned by default.
On a different issue, I think that the emulator may be wrong as it
sometimes fetches values from the DATA segment, even if the CS was
previously selected as the source segment. For exemple, in
x86emu/ops.c, see [*]:
if (M.x86.mode & SYSMODE_PREFIX_DATA) {
u32 destval,srcval;
DECODE_PRINTF("TEST\tDWORD PTR ");
destoffset = decode_rm00_address(rl);
DECODE_PRINTF(",");
srcval = fetch_long_imm();
DECODE_PRINTF2("%x\n", srcval);
destval = fetch_data_long(destoffset);
TRACE_AND_STEP();
test_long(destval, srcval);
} else {
u16 destval,srcval;
DECODE_PRINTF("TEST\tWORD PTR ");
destoffset = decode_rm00_address(rl);
DECODE_PRINTF(",");
srcval = fetch_word_imm();
DECODE_PRINTF2("%x\n", srcval);
destval = fetch_data_word(destoffset); [*]
TRACE_AND_STEP();
test_word(destval, srcval);
}
[*] : shouldn't that be a fetch from the CS segt, since the mode (in
M.x86.mode) is not of the DATA type?
Lastly, I have found that the VGA bios i use is doing CF8/CFC PCI
configuration style accesses. Which doesn't work on my PowerPC plaftorm.
(I think it is only to be seen in the x86 world, but not sure). So they
need to be translated to whatever the platform is going to use as PCI
configuration access. I just mention this for the record in case others
are not aware of this.
Thanks,
-jf simon
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