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arch/x86_64: Clean up stack initialization

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When this code was written, there was no "stack frame" struct defined.
There is now, so use that for clarity and concision.  Also remove an
obvious comment (I mean, duh, we can put any segment selectors in
those fields we want).

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
This commit is contained in:
Andy Ross 2019-02-14 07:53:41 -08:00 • committed by Anas Nashif
commit c9cba3a032
1 changed files with 16 additions and 24 deletions
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40
arch/x86_64/core/xuk.c
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@ -592,32 +592,24 @@ void _cstart64(int cpu_id)
long xuk_setup_stack(long sp, void *fn, unsigned int eflags,
long *args, int nargs)
{
long long *f = (long long *)(sp & ~7) - 20;
struct xuk_stack_frame *f;
/* FIXME: this should extend naturally to setting up usermode
* frames too: the frame should have a SS and RSP at the top
* that specifies the user stack into which to return (can be
* this same stack as long as the mapping is correct), and the
* CS should be a separate ring 3 segment.
*/
/* Align downward and make room for one frame */
f = &((struct xuk_stack_frame *)(sp & ~7))[-1];
f[19] = GDT_SELECTOR(2);
f[18] = sp;
f[17] = eflags;
f[16] = GDT_SELECTOR(1);
f[15] = (long)fn;
f[14] = nargs >= 1 ? args[0] : 0; /* RDI */
f[13] = nargs >= 3 ? args[2] : 0; /* RDX */
f[12] = 0; /* RAX */
f[11] = nargs >= 4 ? args[3] : 0; /* RCX */
f[10] = nargs >= 2 ? args[1] : 0; /* RSI */
f[9] = nargs >= 5 ? args[4] : 0; /* R8 */
f[8] = nargs >= 6 ? args[5] : 0; /* R9 */
/* R10, R11, RBX, RBP, R12, R13, R14, R15 */
for (int i = 7; i >= 0; i--) {
f[i] = 0;
}
*f = (struct xuk_stack_frame) {
.entry.ss = GDT_SELECTOR(2),
.entry.rsp = sp,
.entry.rflags = eflags,
.entry.cs = GDT_SELECTOR(1),
.entry.rip = (long)fn,
.entry.rdi = nargs >= 1 ? args[0] : 0,
.entry.rsi = nargs >= 2 ? args[1] : 0,
.entry.rdx = nargs >= 3 ? args[2] : 0,
.entry.rcx = nargs >= 4 ? args[3] : 0,
.entry.r8 = nargs >= 5 ? args[4] : 0,
.entry.r9 = nargs >= 6 ? args[5] : 0,
};
return (long)f;
}