Date: Sun, 20 Dec 1998 14:01:50 -0500 (EST) From: Alfred Perlstein <bright@hotjobs.com> To: emulation@FreeBSD.ORG Cc: emulators@FreeBSD.ORG Subject: patch for doscmd for illegal lock prefix Message-ID: <Pine.BSF.4.05.9812201352440.6331-100000@bright.fx.genx.net>
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up until a certain stepping point the 'lock' prefix was legal to use on
just about any instruction, however pentium and above severly restrict
its use and generate illegal instruction traps.
i'm unsure of the correctness of the following patch, so could someone
please take a look at it? Anyone want to forward it to the authors?
when an instruction with a 0xF0 prefix (lock) generates a sigILL to doscmd
i patch the opcode to be 0x90 (nop) and retry. i could change IP but the
effect is the same. and this fixes makes the trap go away if it's
encountered in a loop.
this doesn't exactly get my program to run, but it's a step further.
this could also be done to remain more silent.
/usr # diff -u src/usr.bin/doscmd/trap.c.orig src/usr.bin/doscmd/trap.c
--- src/usr.bin/doscmd/trap.c.orig Sun Dec 20 13:14:54 1998
+++ src/usr.bin/doscmd/trap.c Sun Dec 20 13:47:47 1998
@@ -591,9 +591,20 @@
sigill(struct sigframe *sf)
{
regcontext_t *REGS = (regcontext_t *)(&sf->sf_sc);
+ u_char *addr;
fprintf(stderr, "Signal %d from DOS program\n", sf->sf_signum);
+
+ addr = (u_char *)N_GETPTR(R_CS, R_IP);
+ if( *addr == (u_char) 0xf0 ){
+ dump_regs(REGS);
+ fprintf(stderr, "illegal lock prefix, retry with NOP.\n");
+ *addr = (u_char) 0x90;
+ return;
+ }
+
dump_regs(REGS);
+
fatal("%04x:%04x Illegal instruction\n", R_CS, R_IP);
}
btw, it's a pleasure reading doscmd code, really nifty stuff.
later on i get this:
ax=3278 bx=0000 cx=ff05 dx=0306
si=3346 di=0296 sp=8581 bp=0001
cs=0000 ss=1fee ds=9e9e es=f000
ip=4b eflags=b0206
f1 74 07 70 00 0a 00 00 f1 4a 08 70 00 14 00 00
(bad)
unsupported instruction
*sigh* time to break out the i386 manuals :)
Alfred Perlstein - Programmer, HotJobs Inc. - www.hotjobs.com
-- There are operating systems, and then there's FreeBSD.
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