API: Use stack pointer as API signature search hint in the glue layer.

De-hardcode range in RAM we search for the API signature. Instead use the stack
pointer as a hint to narrow down the range in which the signature could reside
(it is malloc'ed on the U-Boot heap, and is hoped to remain in some proximity
from stack area). Adjust PowerPC code in API demo to the new scheme.

Signed-off-by: Rafal Czubak <rcz@semihalf.com>
Signed-off-by: Rafal Jaworowski <raj@semihalf.com>

api_examples/crt0.S

@@ -29,6 +29,9 @@
 
 	.globl _start
 _start:
+	lis	%r11, search_hint@ha
+	addi	%r11, %r11, search_hint@l
+	stw	%r1, 0(%r11)
 	b	main
 
 
@@ -39,12 +42,15 @@ syscall:
 	lwz	%r11, 0(%r11)
 	mtctr	%r11
 	bctr
-
+#else
+#error No support for this arch!
+#endif
 
 	.globl syscall_ptr
 syscall_ptr:
 	.align	4
 	.long	0
-#else
-#error No support for this arch!
-#endif
+
+	.globl search_hint
+search_hint:
+	.long   0

api_examples/glue.c

@@ -60,13 +60,20 @@ static int valid_sig(struct api_signature *sig)
 int api_search_sig(struct api_signature **sig) {
 
 	unsigned char *sp;
+	uint32_t search_start = 0;
+	uint32_t search_end = 0;
 
 	if (sig == NULL)
 		return 0;
 
-	sp = (unsigned char *)API_SEARCH_START;
+	if (search_hint == 0)
+		search_hint = 255 * 1024 * 1024;
 
-	while ((sp + (int)API_SIG_MAGLEN) < (unsigned char *)API_SEARCH_END) {
+	search_start = search_hint & ~0x000fffff;
+	search_end = search_start + API_SEARCH_LEN - API_SIG_MAGLEN;
+
+	sp = (unsigned char *)search_start;
+	while ((sp + API_SIG_MAGLEN) < (unsigned char *)search_end) {
 		if (!memcmp(sp, API_SIG_MAGIC, API_SIG_MAGLEN)) {
 			*sig = (struct api_signature *)sp;
 			if (valid_sig(*sig))

api_examples/glue.h

@@ -30,12 +30,12 @@
 #ifndef _API_GLUE_H_
 #define _API_GLUE_H_
 
-#define API_SEARCH_START	(255 * 1024 * 1024)	/* start at 1MB below top RAM */
-#define API_SEARCH_END		(256 * 1024 * 1024 - 1)	/* ...and search to the end */
+#define API_SEARCH_LEN		(3 * 1024 * 1024)	/* 3MB search range */
 
-int	syscall(int, int *, ...);
-void *	syscall_ptr;
+extern void *syscall_ptr;
+extern uint32_t search_hint;
 
+int	syscall(int, int *, ...);
 int	api_search_sig(struct api_signature **sig);
 
 /*