selftests/bpf: Fix test_attach_probe

Fix two issues in test_attach_probe:

1. it was not able to parse /proc/self/maps beyond the first line,
   since %s means parse string until white space.
2. offset has to be accounted for otherwise uprobed address is incorrect.

Fixes: 1e8611b ("selftests/bpf: add kprobe/uprobe selftests")
Signed-off-by: Alexei Starovoitov <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Yonghong Song <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: Alexei Starovoitov

tools/testing/selftests/bpf/prog_tests/attach_probe.c

@@ -3,18 +3,19 @@
 #include "test_attach_probe.skel.h"
 
 ssize_t get_base_addr() {
-	size_t start;
+	size_t start, offset;
 	char buf[256];
 	FILE *f;
 
 	f = fopen("/proc/self/maps", "r");
 	if (!f)
 		return -errno;
 
-	while (fscanf(f, "%zx-%*x %s %*s\n", &start, buf) == 2) {
+	while (fscanf(f, "%zx-%*x %s %zx %*[^\n]\n",
+		      &start, buf, &offset) == 3) {
 		if (strcmp(buf, "r-xp") == 0) {
 			fclose(f);
-			return start;
+			return start - offset;
 		}
 	}