libpayload: Add an exec() and i386_do_exec() function

Add functions for libpayload to execute other payloads in memory,
and have those functions return cleanly.

Signed-off-by: Jordan Crouse <jordan.crouse@amd.com>
Acked-by: Uwe Hermann <uwe@hermann-uwe.de>


git-svn-id: svn://svn.coreboot.org/coreboot/trunk@3338 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1

3 files changed, 104 insertions, 3 deletions

diff --git a/payloads/libpayload/i386/Makefile.inc b/payloads/libpayload/i386/Makefile.inc
index 90b071ff35..e8d9339880 100644
--- a/payloads/libpayload/i386/Makefile.inc
+++ b/payloads/libpayload/i386/Makefile.inc
@@ -29,3 +29,4 @@
 
 TARGETS-y += i386/head.o i386/main.o i386/sysinfo.o
 TARGETS-y += i386/timer.o i386/coreboot.o i386/util.o
+TARGETS-y += i386/exec.o
diff --git a/payloads/libpayload/i386/exec.S b/payloads/libpayload/i386/exec.S
new file mode 100644
index 0000000000..9a44196e6b
--- /dev/null
+++ b/payloads/libpayload/i386/exec.S
@@ -0,0 +1,99 @@
+/*
+ * This file is part of the libpayload project.
+ *
+ * Copyright (C) 2008 Advanced Micro Devices, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/* calling syntax:  i386_do_exec(long addr, int argc, char **argv, int *ret) */
+
+/* This implements the payload API detailed here:
+ * http://www.coreboot.org/Payload_API
+ */
+
+.align 4
+.text
+
+.global i386_do_exec
+        .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 */
+
+	pushl %esi
+	pushl %ecx
+	pushl %ebp
+
+	/* Push the argc and argv pointers on to the stack */
+
+	movl 12(%ebp), %esi
+	movl 16(%ebp), %ecx
+
+	pushl %esi
+	pushl %ecx
+
+	/* Move a "magic" number on the stack - the other
+	 * payload will use this as a clue that the argc
+	 * and argv are sane
+	 */
+
+	movl  $12345678, %ecx
+	pushl %ecx
+
+	/* Jump to the code */
+	call *%eax
+
+	/* %eax has the return value */
+
+	/* Skip over the argc/argv stuff still on the stack */
+	addl $12, %esp
+
+	/* Get back %ebp */
+	popl %ebp
+
+	/* Get the pointer to the return value
+	 * and save the return value in it
+         */
+
+	movl 20(%ebp), %ecx
+	movl %eax, (%eax)
+
+	/* Get the rest of the saved registers */
+	popl %ecx
+	popl %esi
+	popl %eax
+
+	/* Restore the stack pointer */
+	movl %ebp,%esp
+	popl %ebp
+	ret
+
diff --git a/payloads/libpayload/i386/head.S b/payloads/libpayload/i386/head.S
index 8dc31aa54d..54f60e1469 100644
--- a/payloads/libpayload/i386/head.S
+++ b/payloads/libpayload/i386/head.S
@@ -63,13 +63,14 @@ _init:
 
 	/* Let's rock. */
 	call start_main
-	
+
+	/* %eax has the return value - pass it on unmolested */
 _leave:
 	/* Get old stack pointer. */
 	popl %ebx
 
 	/* Restore old stack. */
-	movl %esp, %ebx
+	movl %ebx, %esp
 
 	/* Return to the original context. */
-	lret
+	ret