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x86: fix stack zeroing when dropping to user mode

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For 'rep stosl' ECX isn't a size value, it's how many times to repeat
the 4-byte string copy operation.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
This commit is contained in:
Andrew Boie 2017-10-05 14:34:24 -07:00 committed by Anas Nashif
parent d5894a17d0
commit 3e3a237930
1 changed files with 5 additions and 4 deletions
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9
arch/x86/core/userspace.S
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@ -120,18 +120,19 @@ SECTION_FUNC(TEXT, _x86_userspace_enter)
push %edi
push %eax
/* Compute size of user stack and put in ECX */
/* Compute size of user stack in 4-byte chunks and put in ECX */
mov %ebx, %ecx
sub %edi, %ecx
shr $2, %ecx /* Divide by 4 */
#ifdef CONFIG_INIT_STACKS
mov $0xAAAAAAAA, %eax
#else
xor %eax, %eax
#endif
/* Fill ECX bytes of memory, 4 bytes at a time, starting at ES:EDI,
* with whatever is in EAX. Stack sizes are always at least 4-byte
* aligned.
/* Copy 4 bytes of memory at a time, starting at ES:EDI, with whatever
* is in EAX. Repeat this ECX times. Stack sizes are always at least
* 4-byte aligned.
*/
cld
rep stosl