Date: Wed, 24 Feb 2010 22:35:40 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: c.jayachandran@gmail.com Cc: freebsd-mips@FreeBSD.org Subject: Re: Writing MIPS assembler instructions in C Message-ID: <20100224.223540.319083499807541849.imp@bsdimp.com> In-Reply-To: <98a59be81002242126k5bbf5167p7cba4917c13d1256@mail.gmail.com> References: <eaa228be1002241807q2613ccecy9773155e68ccda62@mail.gmail.com> <201002250236.o1P2a2oX024250@ns.mahan.org> <98a59be81002242126k5bbf5167p7cba4917c13d1256@mail.gmail.com>
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In message: <98a59be81002242126k5bbf5167p7cba4917c13d1256@mail.gmail.com>
"C. Jayachandran" <c.jayachandran@gmail.com> writes:
: On Thu, Feb 25, 2010 at 8:01 AM, Patrick Mahan <mahan@mahan.org> wrote:
: >
: > > %[foo] can be used to refer to named parameters (input or output,
: > > maybe even clobbered) of inline assembly instructions rather than
: > > using %0, %1, etc., which can be hard to read. Consider:
: > >
: > > The brackets with the input and output parameters specify what names
: > > to use to refer to them in the assembly listing (here they happen to
: > > be mostly the same as the variable names, but that's not necessary.)
: > >
: >
: > Ah Sooo <*whack!*>......
: >
: > I did not even twig on that... I had gotten it in my head that %[rt]
: > was something special to the compiler that caused a certain behavior
: > to occur.
: >
: > Now my problem is I still need to force the value pointed to "addr" into
: > a specific register because there is a jalr to a function else where
: > that I only have binary access too and it expects it's a value in
: > that register. Can I coerce this?
:
: I may be missing something here, but have you tried :
:
: __asm__ __volatile__(
: "ld $8, 0(%0)\n\t"
: "jalr $8\n"
: : : "r"(addr) : "$8");
: }
:
: Or is there a reason this will not work?
Which register do you need to force it into? Maybe it is something as
simple as:
register_t r = *(register_t *)addr;
foo(r);
if that register is a0...
Warner
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