>I have very little assembler/x86 knowledge. >Could anyone please help me understand what it means to assign a >non-zero value to td_retval in a system call when return value of the >call is zero/success? > >I see in syscall() in src/sys/i386/i386/trap.c (btw is this the right >place?) that in such circumstances value from td_retval[] is put into >EAX and EDX registers and PSL_C (carry bit) is cleared in status/flags >register in a stack frame of a calling process. But I don't understand >what it practically means for the calling process. > >Thank you in advance.
The way the handler advice you about syscalls failing is setting (and not clearing as you were saying) the carry bit in eflags register (about ia32). A sort of errno (if you see in a C-coder view) value is set in eax (or, alternatively, edx) to show the reason of failing. There's no way to know where error code is set; you can just verify pratically. You can find all these things on "Programmers handbook". cheers, rookie _______________________________________________ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
