From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <b6595fdb69e8735f753434ec5e814950@swtch.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] pointer to the last TOS
From: "Russ Cox" <rsc@swtch.com>
Date: Thu,  2 Mar 2006 10:24:25 -0500
In-Reply-To: <599f06db0603020657u19643c27nad00cbf2998bf877@mail.gmail.com>
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> I have been doing some experiments and reading some code and I have arrived
> to the (possibly wrong) conclusion that in the stack there is no pointer to the
> TOS before a function was called (I am using 8c)
> If this is true, how is the state of the stack
> recovered after return?. Can anyone point me to a place where I can read
> some documentation or something to solve this kind of doubt.

In the Plan 9 C compiler each stack frame has a constant size.
The beginning of a function does SUBL $XXX, SP
and then the end of a function does ADDL $XXX, SP
to restore the stack pointer before returning.
If you compile and then disassemble using acid
you will see the instructions.  They don't appear in the
8c -S output explicitly.  Instead the TEXT line specifies
the frame size (TEXT f(SB), 0, $XXX) and the linker
inserts the necessary instructions.

Russ