[PATCH 3/4] selftests/arm: Add elf test

[Dev Jain]

This patch introduces an ELF parsing test; the 5th byte of the ELF header
must be 0x01 for a 32-bit process. A basic sanity check is required to ensure
that we are actually testing a 32-bit build.

Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
---
 tools/testing/selftests/arm/elf/parse_elf.c | 75 +++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 tools/testing/selftests/arm/elf/parse_elf.c

diff --git a/tools/testing/selftests/arm/elf/parse_elf.c b/tools/testing/selftests/arm/elf/parse_elf.c
new file mode 100644
index 000000000000..decd65699858
--- /dev/null
+++ b/tools/testing/selftests/arm/elf/parse_elf.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2024 ARM Limited
+ *
+ * Author : Dev Jain <dev.jain@xxxxxxx>
+ *
+ * Parse elf header to confirm 32-bit process
+ */
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <elf.h>
+#include <stdint.h>
+
+#include <kselftest.h>
+
+/* The ELF file header.  This appears at the start of every ELF file. */
+
+struct elf_header {
+	unsigned char	e_ident[16];	/* Magic number and other info */
+	uint16_t	e_type;		/* Object file type */
+	uint16_t	e_machine;	/* Architecture */
+	uint32_t	e_version;	/* Object file version */
+	uint64_t	e_entry;	/* Entry point virtual address */
+	uint64_t	e_phoff;	/* Program header table file offset */
+	uint64_t	e_shoff;	/* Section header table file offset */
+	uint32_t	e_flags;	/* Processor-specific flags */
+	uint16_t	e_ehsize;	/* ELF header size in bytes */
+	uint16_t	e_phentsize;	/* Program header table entry size */
+	uint16_t	e_phnum;	/* Program header table entry count */
+	uint16_t	e_shentsize;	/* Section header table entry size */
+	uint16_t	e_shnum;	/* Section header table entry count */
+	uint16_t	e_shstrndx;	/* Section header string table index */
+};
+
+static int read_elf_header(const char  *elfFile)
+{
+	struct elf_header header;
+	FILE *file;
+
+	file = fopen(elfFile, "r");
+	if (file) {
+
+		/* store header in struct */
+		fread(&header, 1, sizeof(header), file);
+		fclose(file);
+
+		/* sanity check: does it really follow ELF format */
+		if (header.e_ident[0] == 0x7f &&
+		    header.e_ident[1] == 'E' &&
+		    header.e_ident[2] == 'L' &&
+		    header.e_ident[3] == 'F') {
+			if (header.e_ident[4] == 0x01)
+				return 0;
+			return 1;
+		}
+		ksft_exit_fail_msg("Cannot parse /proc/self/exe\n");
+	}
+	ksft_exit_fail_msg("Cannot open /proc/self/exe\n");
+	exit(EXIT_FAILURE);
+}
+
+int main(int argc, char *argv[])
+{
+	const char *file_name;
+
+	ksft_print_header();
+	ksft_set_plan(1);
+
+	file_name = "/proc/self/exe";
+	ksft_test_result(read_elf_header(file_name) == 0, "ELF is 32 bit\n");
+	ksft_finished();
+}
-- 
2.39.2