I have found another piece of code I don't understand in the kernel.
syscalls are all fed through a single trap, and the common code which
processes them performs a waserror():
/sys/src/9/pc/trap.c:694
A few lines down this function (after the system call has been
executed up->nerrlab is checked to ensure we have matching
poperror()s for each waserror() during the execution of said call.
this is fine for most calls, however rfork() explicitly sets up->nerrlab
to zero rather than copying it and memmove()ing up->errlab from the parent
proc to the child:
/sys/src/9/port/sysproc.c:90
Surely this means that rfork will always fail with a "bad errstack [19]: -1
extra"
error?
Clearly this doesn't happen but I doin't understand how why it works.
anyone?
-Steve
