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Update comment about 'struct reg' and __greg alignment, and clarify

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the comment about the syscall/trap entry substituting %r10 for %rcx.
This commit is contained in:
dsl 2008-02-06 22:02:17 +00:00
parent d7f6ec471c
commit a87338a03c
1 changed files with 7 additions and 6 deletions
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13
sys/arch/amd64/include/frame_regs.h
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@ -1,4 +1,4 @@
/* $NetBSD: frame_regs.h,v 1.3 2008/01/05 12:08:51 dsl Exp $ */
/* $NetBSD: frame_regs.h,v 1.4 2008/02/06 22:02:17 dsl Exp $ */
#ifndef _AMD64_FRAME_REGS_H_
#define _AMD64_FRAME_REGS_H_
@ -16,14 +16,15 @@
* 2) src/lib/libc/arch/x86_64/gen/makecontext.c assumes that the first
* 6 entries in the __greg_t array match the registers used to pass
* function arguments.
* 3) PTHREAD_UCONTEXT_TO_REG (src/lib/libpthread/arch/?*?/pthread_md.h)
* assumes that something matches the __greg_t layout, but there
* are no (obvious) references.
* 3) The 'struct reg' from machine/reg.h has to match __greg_t.
* Since they are both arrays and indexed with the same tokens this
* shouldn't be a problem, but is rather confusing.
* This assumption is made in a lot of places!
* 4) There might be other code out there that relies on the ordering.
*
* The first entries below match the registers used for syscall arguments
* (%rcx is destroyed by the syscall instruction, to the libc stubs copy
* the value to %r10).
* (%rcx is destroyed by the syscall instruction, the libc system call
* stubs copy %rcx to %r10).
* arg6-arg9 are copied from the user stack for system calls with more
* than 6 args (SYS_MAXSYSARGS is 8, + 2 entries for SYS___SYSCALL).
*/