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Date: Wed, 19 Aug 2015 22:18:00 -0000
From: Segher Boessenkool <segher@kernel.crashing.org>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: Mike Stump <mikestump@comcast.net>, GCC Patches <gcc-patches@gcc.gnu.org>,        Uros Bizjak <ubizjak@gmail.com>
Subject: Re: [PATCH] Add __builtin_stack_top
Message-ID: <20150819221029.GB26407@gate.crashing.org>
References: <CAMe9rOoMzgkguZ+zY24Jytpr9HnoXvu5BUP3c7K-34Gmm2SDLg@mail.gmail.com> <CAMe9rOrHUnJJx68qKUe0gsVVwYXNALmCR6-4UVV_V3df4KO3_A@mail.gmail.com> <20150819125145.GC8652@gate.crashing.org> <CAMe9rOrymZ3N_2HTd87C-LfoHYeZ_P7myMCL9ZvikE+uU19eRg@mail.gmail.com> <CAMe9rOqLxX3h_Pn2Rn1Ph-FH41e1DfEG1qPheDLBNdycPa=sNw@mail.gmail.com> <20150819165854.GB32473@gate.crashing.org> <CAMe9rOqDjBKWXcA7mYXeCoktUj4Q5FRWiDq+rxKRTyZiyXRBTQ@mail.gmail.com> <20150819174805.GC32473@gate.crashing.org> <CAMe9rOoOiWQGrTey+J54=JRVd0wK9p65HEj0s8F1nkx0+1qg=A@mail.gmail.com> <CAMe9rOqo-VSwuQNgApWKK-1saPwtX4KrHwZOB3w=nsQJv3dPjA@mail.gmail.com>
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On Wed, Aug 19, 2015 at 02:53:47PM -0700, H.J. Lu wrote:
> How about this
> 
> @deftypefn {Built-in Function} {void *} __builtin_argument_pointer (void)
> This function is similar to @code{__builtin_frame_address} with an
> argument of 0, but it returns the address of the incoming arguments to
> the current function rather than the address of its frame.  Unlike
> @code{__builtin_frame_address}, the frame pointer register isn't
> required.

That last line isn't true, if your port uses INITIAL_FRAME_POINTER_RTX.
Maybe it shouldn't be true otherwise either (but currently a hard frame
pointer is forced, indeed).  Have we gone full circle now? ;-)

> The exact definition of this address depends upon the processor and the
> calling convention.  Usually some arguments are passed in registers and
> the rest on the stack, and this builtin returns the address of the
> first argument which would be passed on the stack.
> @end deftypefn


Segher