Mathias Krause (minipli@googlemail.com) just uploaded a new patch set to gerrit, which you can find at https://review.coreboot.org/18335
-gerrit
commit b8df53bcbdaf7200a2a93caf042578b0f3fbfa49 Author: Mathias Krause minipli@googlemail.com Date: Sat Feb 11 21:02:08 2017 +0100
libpayload: x86/exec - simplify and robustify the code
Simplify the code by directly using the arguments on the stack as base pointer relative memory references, instead of loading them into intermediate registers first.
Make it more robust by preserving all callee saved registers mandated by the C calling convention (and only those), namely EBP, EBX, ESI and EDI.
Don't assume anything about the register state when the called function returns -- beside the segment registers and the stack pointer to be still the same as before the call.
Change-Id: I383d6ccefc5b3d5cca37a1c9b638c231bbc48aa8 Signed-off-by: Mathias Krause minipli@googlemail.com --- payloads/libpayload/arch/x86/exec.S | 59 +++++++++++++------------------------ 1 file changed, 20 insertions(+), 39 deletions(-)
diff --git a/payloads/libpayload/arch/x86/exec.S b/payloads/libpayload/arch/x86/exec.S index 54c83f6..f5cb0e3 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