1// SPDX-License-Identifier: GPL-2.0
 2#include <byteswap.h>
 3#include <elf.h>
 4#include <endian.h>
 5#include <inttypes.h>
 6#include <stdint.h>
 7#include <stdio.h>
 8#include <stdlib.h>
 9#include <string.h>
10
11#ifdef be32toh
12/* If libc provides [bl]e{32,64}toh() then we'll use them */
13#elif BYTE_ORDER == LITTLE_ENDIAN
14# define be32toh(x)	bswap_32(x)
15# define le32toh(x)	(x)
16# define be64toh(x)	bswap_64(x)
17# define le64toh(x)	(x)
18#elif BYTE_ORDER == BIG_ENDIAN
19# define be32toh(x)	(x)
20# define le32toh(x)	bswap_32(x)
21# define be64toh(x)	(x)
22# define le64toh(x)	bswap_64(x)
23#endif
24
25__attribute__((noreturn))
26static void die(const char *msg)
27{
28	fputs(msg, stderr);
29	exit(EXIT_FAILURE);
30}
31
32int main(int argc, const char *argv[])
33{
34	uint64_t entry;
35	size_t nread;
36	FILE *file;
37	union {
38		Elf32_Ehdr ehdr32;
39		Elf64_Ehdr ehdr64;
40	} hdr;
41
42	if (argc != 2)
43		die("Usage: elf-entry <elf-file>\n");
44
45	file = fopen(argv[1], "r");
46	if (!file) {
47		perror("Unable to open input file");
48		return EXIT_FAILURE;
49	}
50
51	nread = fread(&hdr, 1, sizeof(hdr), file);
52	if (nread != sizeof(hdr)) {
53		perror("Unable to read input file");
54		return EXIT_FAILURE;
55	}
56
57	if (memcmp(hdr.ehdr32.e_ident, ELFMAG, SELFMAG))
58		die("Input is not an ELF\n");
59
60	switch (hdr.ehdr32.e_ident[EI_CLASS]) {
61	case ELFCLASS32:
62		switch (hdr.ehdr32.e_ident[EI_DATA]) {
63		case ELFDATA2LSB:
64			entry = le32toh(hdr.ehdr32.e_entry);
65			break;
66		case ELFDATA2MSB:
67			entry = be32toh(hdr.ehdr32.e_entry);
68			break;
69		default:
70			die("Invalid ELF encoding\n");
71		}
72
73		/* Sign extend to form a canonical address */
74		entry = (int64_t)(int32_t)entry;
75		break;
76
77	case ELFCLASS64:
78		switch (hdr.ehdr32.e_ident[EI_DATA]) {
79		case ELFDATA2LSB:
80			entry = le64toh(hdr.ehdr64.e_entry);
81			break;
82		case ELFDATA2MSB:
83			entry = be64toh(hdr.ehdr64.e_entry);
84			break;
85		default:
86			die("Invalid ELF encoding\n");
87		}
88		break;
89
90	default:
91		die("Invalid ELF class\n");
92	}
93
94	printf("0x%016" PRIx64 "\n", entry);
95	return EXIT_SUCCESS;
96}