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-rw-r--r--payloads/libpayload/arch/x86/exec.S59
1 files changed, 20 insertions, 39 deletions
diff --git a/payloads/libpayload/arch/x86/exec.S b/payloads/libpayload/arch/x86/exec.S
index 54c83f653e..f5cb0e3398 100644
--- a/payloads/libpayload/arch/x86/exec.S
+++ b/payloads/libpayload/arch/x86/exec.S
@@ -37,67 +37,48 @@
.text
.global i386_do_exec
- .type i386_do_exec,@function
+ .type i386_do_exec,@function
i386_do_exec:
pushl %ebp
movl %esp, %ebp
- pushl %eax
-
- /* Put the run address in %eax */
- movl 8(%ebp), %eax
-
- /* Save off the rest of the registers */
+ /* Save the remaining callee preserved registers */
+ pushl %ebx
pushl %esi
- pushl %ecx
- pushl %ebp
+ pushl %edi
/* Push argc and argv on to the stack.
*
* We need to put a dummy value inbetween, as argc should be at offset
* 0x10, according to the payload API.
*/
-
- movl 12(%ebp), %esi
- movl 16(%ebp), %ecx
-
- pushl %esi
+ pushl 12(%ebp)
pushl $0
- pushl %ecx
+ pushl 16(%ebp)
- /* Move a "magic" number on the stack - the other
- * payload will use this as a clue that the argc
- * and argv are sane
+ /* Push a "magic" number on the stack - the other payload will use this
+ * as a clue that the argc and argv values on the stack are sane.
*/
-
- movl $0x12345678, %ecx
- pushl %ecx
+ pushl $0x12345678
/* Jump to the code */
- call *%eax
-
+ call *8(%ebp)
/* %eax has the return value */
- /* Skip over the argc/argv stuff still on the stack */
- addl $12, %esp
+ /* Skip over the argc/argv stuff still on the stack.
+ * Don't assume %ebp is sane, here. Restore it from the stack.
+ */
+ addl $0x10, %esp
- /* Get back %ebp */
+ /* Restore the saved registers */
+ popl %edi
+ popl %esi
+ popl %ebx
popl %ebp
- /* Get the pointer to the return value
- * and save the return value in it
- */
-
- movl 20(%ebp), %ecx
+ /* Get pointer to return value and save the return value in it. */
+ movl 16(%esp), %ecx
movl %eax, (%ecx)
- /* Get the rest of the saved registers */
- popl %ecx
- popl %esi
- popl %eax
-
- /* Restore the stack pointer */
- movl %ebp,%esp
- popl %ebp
ret