x86: fix stack zeroing when dropping to user mode
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>
diff --git a/arch/x86/core/userspace.S b/arch/x86/core/userspace.S
index f06d336..188441a 100644
--- a/arch/x86/core/userspace.S
+++ b/arch/x86/core/userspace.S
@@ -120,18 +120,19 @@
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
