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)) 26 static void die(const char *msg) 27 { 28 fputs(msg, stderr); 29 exit(EXIT_FAILURE); 30 } 31 32 int 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 fclose(file); 55 return EXIT_FAILURE; 56 } 57 58 if (memcmp(hdr.ehdr32.e_ident, ELFMAG, SELFMAG)) { 59 fclose(file); 60 die("Input is not an ELF\n"); 61 } 62 63 switch (hdr.ehdr32.e_ident[EI_CLASS]) { 64 case ELFCLASS32: 65 switch (hdr.ehdr32.e_ident[EI_DATA]) { 66 case ELFDATA2LSB: 67 entry = le32toh(hdr.ehdr32.e_entry); 68 break; 69 case ELFDATA2MSB: 70 entry = be32toh(hdr.ehdr32.e_entry); 71 break; 72 default: 73 fclose(file); 74 die("Invalid ELF encoding\n"); 75 } 76 77 /* Sign extend to form a canonical address */ 78 entry = (int64_t)(int32_t)entry; 79 break; 80 81 case ELFCLASS64: 82 switch (hdr.ehdr32.e_ident[EI_DATA]) { 83 case ELFDATA2LSB: 84 entry = le64toh(hdr.ehdr64.e_entry); 85 break; 86 case ELFDATA2MSB: 87 entry = be64toh(hdr.ehdr64.e_entry); 88 break; 89 default: 90 fclose(file); 91 die("Invalid ELF encoding\n"); 92 } 93 break; 94 95 default: 96 fclose(file); 97 die("Invalid ELF class\n"); 98 } 99 100 printf("0x%016" PRIx64 "\n", entry); 101 fclose(file); 102 return EXIT_SUCCESS; 103 } 104