From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <30e8c9fe88deefa3ede46aec7b2f75c8@quintile.net>
From: "Steve Simon" <steve@quintile.net>
Date: Wed, 13 Aug 2008 00:13:21 +0100
To: 9fans@9fans.net
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Subject: [9fans] another kernel question
Topicbox-Message-UUID: fd8c864a-ead3-11e9-9d60-3106f5b1d025

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