libbpf: Support Debian in resolve_full_path()

attach_probe selftest fails on Debian-based distros with `failed to
resolve full path for 'libc.so.6'`. The reason is that these distros
embraced multiarch to the point where even for the "main" architecture
they store libc in /lib/<triple>.

This is configured in /etc/ld.so.conf and in theory it's possible to
replicate the loader's parsing and processing logic in libbpf, however
a much simpler solution is to just enumerate the known library paths.

Signed-off-by: Ilya Leoshkevich <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: iii-i

tools/lib/bpf/libbpf.c

@@ -10707,15 +10707,53 @@ static long elf_find_func_offset(const char *binary_path, const char *name)
 	return ret;
 }
 
+static const char *arch_specific_lib_paths(void)
+{
+	/*
+	 * Based on https://packages.debian.org/sid/libc6.
+	 *
+	 * Assume that the traced program is built for the same architecture
+	 * as libbpf, which should cover the vast majority of cases.
+	 */
+#if defined(__x86_64__)
+	return "/lib/x86_64-linux-gnu";
+#elif defined(__i386__)
+	return "/lib/i386-linux-gnu";
+#elif defined(__s390x__)
+	return "/lib/s390x-linux-gnu";
+#elif defined(__s390__)
+	return "/lib/s390-linux-gnu";
+#elif defined(__arm__) && defined(__SOFTFP__)
+	return "/lib/arm-linux-gnueabi";
+#elif defined(__arm__) && !defined(__SOFTFP__)
+	return "/lib/arm-linux-gnueabihf";
+#elif defined(__aarch64__)
+	return "/lib/aarch64-linux-gnu";
+#elif defined(__mips__) && defined(__MIPSEL__) && _MIPS_SZLONG == 64
+	return "/lib/mips64el-linux-gnuabi64";
+#elif defined(__mips__) && defined(__MIPSEL__) && _MIPS_SZLONG == 32
+	return "/lib/mipsel-linux-gnu";
+#elif defined(__powerpc64__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+	return "/lib/powerpc64le-linux-gnu";
+#elif defined(__sparc__) && defined(__arch64__)
+	return "/lib/sparc64-linux-gnu";
+#elif defined(__riscv) && __riscv_xlen == 64
+	return "/lib/riscv64-linux-gnu";
+#else
+	return NULL;
+#endif
+}
+
 /* Get full path to program/shared library. */
 static int resolve_full_path(const char *file, char *result, size_t result_sz)
 {
-	const char *search_paths[2];
+	const char *search_paths[3] = {};
 	int i;
 
 	if (strstr(file, ".so")) {
 		search_paths[0] = getenv("LD_LIBRARY_PATH");
 		search_paths[1] = "/usr/lib64:/usr/lib";
+		search_paths[2] = arch_specific_lib_paths();
 	} else {
 		search_paths[0] = getenv("PATH");
 		search_paths[1] = "/usr/bin:/usr/sbin";