From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753562AbZBCSXT (ORCPT ); Tue, 3 Feb 2009 13:23:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751384AbZBCSXK (ORCPT ); Tue, 3 Feb 2009 13:23:10 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:32957 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751010AbZBCSXI (ORCPT ); Tue, 3 Feb 2009 13:23:08 -0500 Date: Tue, 3 Feb 2009 19:22:56 +0100 From: Ingo Molnar To: linux-kernel@vger.kernel.org Cc: "H. Peter Anvin" , Thomas Gleixner Subject: [tip:x86/asm] x86: document 64-bit and 32-bit function call convention ABI Message-ID: <20090203182256.GA1061@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org - also clean up the calling.h file a tiny bit Signed-off-by: Ingo Molnar --- arch/x86/include/asm/calling.h | 56 +++++++++++++++++++++++++++++++++++++-- 1 files changed, 53 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h index 2bc162e..2d36d42 100644 --- a/arch/x86/include/asm/calling.h +++ b/arch/x86/include/asm/calling.h @@ -1,5 +1,55 @@ /* - * Some macros to handle stack frames in assembly. + + x86 function call convention, 64-bit: + ------------------------------------- + arguments | callee-saved | extra caller-saved | return + [callee-clobbered] | | [callee-clobbered] | + --------------------------------------------------------------------------- + rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**] + + ( rsp is obviously invariant across normal function calls. (gcc can 'merge' + functions when it sees tail-call optimization possibilities) rflags is + clobbered. Leftover arguments are passed over the stack frame.) + + [*] In the frame-pointers case ebp is fixed to the stack frame. + + [**] for struct return values wider than 64 bits the return convention is a + bit more complex: up to 128 bits width we return small structures + straight in rax, rdx. For structures larger than that (3 words or + larger) the caller puts a pointer to an on-stack return struct + [allocated in the caller's stack frame] into the first argument - i.e. + into rdi. All other arguments shift up by one in this case. + Fortunately this case is rare in the kernel. + +For 32-bit we have the following conventions - kernel is build with +-mregparm=3 and -freg-struct-return: + + x86 function calling convention, 32-bit: + ---------------------------------------- + arguments | callee-saved | extra caller-saved | return + [callee-clobbered] | | [callee-clobbered] | + ------------------------------------------------------------------------- + eax edx ecx | ebx edi esi ebp [*] | | eax, edx [**] + + ( here too esp is obviously invariant across normal function calls. eflags + is clobbered. Leftover arguments are passed over the stack frame. ) + + [*] In the frame-pointers case ebp is fixed to the stack frame. + + [**] We build with -freg-struct-return, which on 32-bit means similar + semantics as on 64-bit: edx can be used for a second return value + (i.e. covering integer and structure sizes up to 64 bits) - after that + it gets more complex and more expensive: 3-word or larger struct returns + get done in the caller's frame and the pointer to the return struct goes + into regparm0, i.e. eax - the other arguments shift up and the + function's register parameters degenerate to regparm=2 in essence. + +*/ + + +/* + * 64-bit system call stack frame layout defines and helpers, + * for assembly code: */ #define R15 0 @@ -9,7 +59,7 @@ #define RBP 32 #define RBX 40 -/* arguments: interrupts/non tracing syscalls only save upto here*/ +/* arguments: interrupts/non tracing syscalls only save upto here: */ #define R11 48 #define R10 56 #define R9 64 @@ -22,7 +72,7 @@ #define ORIG_RAX 120 /* + error_code */ /* end of arguments */ -/* cpu exception frame or undefined in case of fast syscall. */ +/* cpu exception frame or undefined in case of fast syscall: */ #define RIP 128 #define CS 136 #define EFLAGS 144