Hi, I found that running with the FreeDOS kernel (tested on build 2038 from 2008-03-08 as available on Rugxulo's site) my program sometimes mysteriously enabled the Trace Flag when returning from a child process. This does not happen in MS-DOS. MS-DOS (tested 6.22 and 7.10) apparently does not use the flags on the parent's stack frame when returning, it instead sets some default flags. These default flags ignore the Carry Flag and Trace Flag as stored on the parent's stack frame, both are always cleared. The stored Interrupt Flag is ignored too, it's always set.
During execution of my program's child process, my program fails to properly preserve its own stack for DOS to use. To be clear, the stack contents are lost - the stack itself is free and usable at the time the child process terminates. This is not a problem in MS-DOS, because cs:ip and the flags are properly set (with the Trace Flag always off) and my program does not depend on any of the registers to be preserved. The appropriate place for a patch would be in the function return_user() in task.c, near the end, where cs:ip on the parent's stack is reset to the stored Int22 handler. Adding this line might be sufficient: irp->FLAGS = 0x200; /* clear the Trace Flag and Carry Flag. set the Interrupt Flag */ (There's no definition FLG_INTERRUPT in pcb.h so I used the immediate value.) Regards, Christian ------------------------------------------------------------------------------ Nokia and AT&T present the 2010 Calling All Innovators-North America contest Create new apps & games for the Nokia N8 for consumers in U.S. and Canada $10 million total in prizes - $4M cash, 500 devices, nearly $6M in marketing Develop with Nokia Qt SDK, Web Runtime, or Java and Publish to Ovi Store http://p.sf.net/sfu/nokia-dev2dev _______________________________________________ Freedos-kernel mailing list Freedos-kernel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-kernel
