From: Giacomo Tesio <giacomo@tesio.it>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: [9fans] FP register usage in Plan9 assembler
Date: Mon, 1 Feb 2016 17:47:46 +0100 [thread overview]
Message-ID: <CAHL7psFg6JgatGw3hQb93kpkrZFGq7vtcz7eMkWWbM0cNfMGzA@mail.gmail.com> (raw)
[-- Attachment #1: Type: text/plain, Size: 1495 bytes --]
I'm studying the 9front's amd64 kernel, and I'm pretty new to assembler
programming, so sorry if my question is too dumb...
I cannot understand the FP pseudo register usage.
The cpuid function, for example, is implemented as
/*
* The CPUID instruction is always supported on the amd64.
*/
TEXT cpuid(SB), $-4
MOVL RARG, AX /* function in AX */
CPUID
MOVQ info+8(FP), BP
MOVL AX, 0(BP)
MOVL BX, 4(BP)
MOVL CX, 8(BP)
MOVL DX, 12(BP)
RET
What I miss is where "info" comes from. I cannot
Apparently the GAS equivalent is:
.align 4
.globl cpuid
cpuid:
mov %ebp,%eax
cpuid
mov 0x10(%rsp),%rbp
mov %eax,0x0(%rbp)
mov %ebx,0x4(%rbp)
mov %ecx,0x8(%rbp)
mov %edx,0xc(%rbp)
retq
Thus apparently info+8(FP) becomes 0x10(%rsp)
Why? I know that FP is a pseudo register, but shouldn't it be different
from SP?
And why info's value is 8? Is it the pointer size?
Another example:
TEXT insb(SB), 1, $-4
MOVL RARG, DX /* MOVL port+0(FP), DX */
MOVQ address+8(FP), DI
MOVL count+16(FP), CX
CLD
REP; INSB
RET
should be equivalent to
.align 4
.globl insb
insb:
mov %ebp,%edx
mov 0x10(%rsp),%rdi
mov 0x18(%rsp),%ecx
cld
rep insb
retq
Again I cannot find a definition of address and count, but both seem to be
be valued as 8, why?
Giacomo
[-- Attachment #2: Type: text/html, Size: 2516 bytes --]
next reply other threads:[~2016-02-01 16:47 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-01 16:47 Giacomo Tesio [this message]
2016-02-01 22:38 ` Charles Forsyth
2016-02-01 22:44 ` Charles Forsyth
2016-02-01 22:48 ` cinap_lenrek
2016-02-01 23:34 ` Giacomo Tesio
2016-02-02 0:36 ` Charles Forsyth
2016-02-02 0:58 ` Giacomo Tesio
2016-02-02 12:39 ` Aram Hăvărneanu
2016-02-02 16:42 ` Steven Stallion
2016-02-02 17:16 ` lucio
2016-02-03 15:24 ` erik quanstrom
2016-02-03 15:51 ` Steven Stallion
2016-02-03 16:36 ` erik quanstrom
2016-02-04 10:08 ` Aram Hăvărneanu
2016-02-04 12:04 ` lucio
2016-02-04 15:58 ` Ryan Gonzalez
2016-02-04 16:09 ` lucio
2016-02-04 18:06 ` Ryan Gonzalez
2016-02-04 18:14 ` balaji
2016-02-04 18:28 ` Ryan Gonzalez
2016-02-04 19:31 ` Skip Tavakkolian
2016-02-04 12:24 ` Brantley Coile
2016-02-04 12:53 ` lucio
2016-02-04 14:57 ` erik quanstrom
2016-02-04 14:05 ` Aram Hăvărneanu
2016-02-04 14:10 ` Aram Hăvărneanu
2016-02-04 14:30 ` Aram Hăvărneanu
2016-02-04 15:07 ` Charles Forsyth
2016-02-04 15:16 ` erik quanstrom
2016-02-04 15:11 ` erik quanstrom
2016-02-04 15:22 ` erik quanstrom
2016-02-04 15:26 ` Charles Forsyth
2016-02-04 20:34 ` erik quanstrom
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAHL7psFg6JgatGw3hQb93kpkrZFGq7vtcz7eMkWWbM0cNfMGzA@mail.gmail.com \
--to=giacomo@tesio.it \
--cc=9fans@9fans.net \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).