diff options
| -rw-r--r-- | payloads/libpayload/arch/x86/exec.S | 59 |
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 |