selftests/powerpc: Refactor the AUXV routines

Refactor the AUXV routines so they are more composable. In a future test
we want to look for many AUXV entries and we don't want to have to read
/proc/self/auxv each time.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/include/utils.h

@@ -24,7 +24,11 @@ typedef uint8_t u8;
 
 void test_harness_set_timeout(uint64_t time);
 int test_harness(int (test_function)(void), char *name);
-extern void *get_auxv_entry(int type);
+
+int read_auxv(char *buf, ssize_t buf_size);
+void *find_auxv_entry(int type, char *auxv);
+void *get_auxv_entry(int type);
+
 int pick_online_cpu(void);
 
 static inline bool have_hwcap(unsigned long ftr)

tools/testing/selftests/powerpc/utils.c

@@ -19,45 +19,64 @@
 
 static char auxv[4096];
 
-void *get_auxv_entry(int type)
+int read_auxv(char *buf, ssize_t buf_size)
 {
-	ElfW(auxv_t) *p;
-	void *result;
 	ssize_t num;
-	int fd;
+	int rc, fd;
 
 	fd = open("/proc/self/auxv", O_RDONLY);
 	if (fd == -1) {
 		perror("open");
-		return NULL;
+		return -errno;
 	}
 
-	result = NULL;
-
-	num = read(fd, auxv, sizeof(auxv));
+	num = read(fd, buf, buf_size);
 	if (num < 0) {
 		perror("read");
+		rc = -EIO;
 		goto out;
 	}
 
-	if (num > sizeof(auxv)) {
-		printf("Overflowed auxv buffer\n");
+	if (num > buf_size) {
+		printf("overflowed auxv buffer\n");
+		rc = -EOVERFLOW;
 		goto out;
 	}
 
+	rc = 0;
+out:
+	close(fd);
+	return rc;
+}
+
+void *find_auxv_entry(int type, char *auxv)
+{
+	ElfW(auxv_t) *p;
+
 	p = (ElfW(auxv_t) *)auxv;
 
 	while (p->a_type != AT_NULL) {
-		if (p->a_type == type) {
-			result = (void *)p->a_un.a_val;
-			break;
-		}
+		if (p->a_type == type)
+			return p;
 
 		p++;
 	}
-out:
-	close(fd);
-	return result;
+
+	return NULL;
+}
+
+void *get_auxv_entry(int type)
+{
+	ElfW(auxv_t) *p;
+
+	if (read_auxv(auxv, sizeof(auxv)))
+		return NULL;
+
+	p = find_auxv_entry(type, auxv);
+	if (p)
+		return (void *)p->a_un.a_val;
+
+	return NULL;
 }
 
 int pick_online_cpu(void)