commit: b92d4495d9ee7661b8c5b75648821291b5f5cbfd
Author: Anthony G. Basile <blueness <AT> gentoo <DOT> org>
AuthorDate: Tue Jan 6 20:43:01 2015 +0000
Commit: Anthony G. Basile <blueness <AT> gentoo <DOT> org>
CommitDate: Tue Jan 6 20:43:01 2015 +0000
URL:
http://sources.gentoo.org/gitweb/?p=proj/elfix.git;a=commit;h=b92d4495
misc/elf-abi: manually read little/big endian half or full words
When reading on a native system, read() transparently reads two
byte or four bytes in the correct byte order and returns the correct
value. But if you read() a word in a big endian file from a little
endian system or vice versa, you get the wrong value. We wrap
read() in read_endian() to compensate for this.
---
misc/elf-abi/elf-abi.c | 133 +++++++++++++++++++++++++++++++------------------
1 file changed, 84 insertions(+), 49 deletions(-)
diff --git a/misc/elf-abi/elf-abi.c b/misc/elf-abi/elf-abi.c
index 5f47212..f4408cb 100644
--- a/misc/elf-abi/elf-abi.c
+++ b/misc/elf-abi/elf-abi.c
@@ -58,39 +58,62 @@
#include <unistd.h>
#include <fcntl.h>
-/* We reorder the big endian EM_ numbers to avoid also reading endian
information from
- * the Elf file. For a mapping between common macine names and EM_ see
<elf.h>. For a
- * more complete mapping, see elfutil's machines[] defined in
libebl/eblopenbackend.c.
+/* For a mapping between common macine names and EM_ number see <elf.h>. For
a more
+ * complete mapping, see elfutil's machines[] defined in
libebl/eblopenbackend.c.
*/
#define ELFMAG "\177ELF"
#define ELFCLASS32 1 /* 32-bit objects */
#define ELFCLASS64 2 /* 64-bit objects */
+#define ELFDATA2LSB 1 /* 2's complement, little endian */
+#define ELFDATA2MSB 2 /* 2's complement, big endian */
#define EM_ALPHA 0x9026 /* alpha */
#define EM_ARM 40 /* arm */
#define EM_AARCH64 183 /* arm64 */
-#define EM_PARISC_BE 0x0F00 /* hppa - big endian reordering of
EM_PARISC = 15 */
+#define EM_PARISC 15 /* hppa */
#define EM_IA_64 50 /* ia64 */
-#define EM_68K_BE 0x0400 /* m68k - big endian reordering of
EM_68K = 4 */
-
+#define EM_68K 4 /* m68k */
#define EM_MIPS 8 /* mips */
-#define EM_MIPS_BE 0x800 /* mips - big endian reordering of
EM_MIPS = 8 */
-
-#define EM_PPC_BE 0x1400 /* ppc - big endian reordering of
EM_PPC = 20 */
-#define EM_PPC64_BE 0x1500 /* ppc64 - bit endian reordering of
EM_PPC64 = 21 */
-#define EM_S390_BE 0x1600 /* s390 - big endian reordering of
EM_S390 */
+#define EM_PPC 20 /* ppc */
+#define EM_PPC64 21 /* ppc64 */
+#define EM_S390 22 /* s390 */
#define EM_SH 42 /* Hitachi SH */
-#define EM_SPARC32_BE 0x1200 /* sparc - big endian reordering of
EM_SPARC32PLUS = 18 */
-#define EM_SPARC64_BE 0x2B00 /* sparc - big endian reordinger of
EM_SPARCV9 = 43 */
+#define EM_SPARC32PLUS 18 /* sparc 32-bit */
+#define EM_SPARCV9 43 /* sparc 64-bit */
#define EM_386 3 /* x86 */
#define EM_X86_64 62 /* amd64 */
/* The arm and mips ABI flags housed in e_flags */
-#define EF_MIPS_ABI2 0x00000020 /* Mask for mips ABI */
-#define EF_MIPS_ABI2_BE 0x20000000 /* Mask for mips ABI */
+#define EF_MIPS_ABI2 0x00000020 /* Mask for mips n32 ABI */
#define EF_ARM_EABIMASK 0XFF000000 /* Mask for arm EABI -
we dont' destinguish versions */
+int
+get_wordsize(uint8_t ei_class)
+{
+ switch (ei_class) {
+ case ELFCLASS32:
+ return 32;
+ case ELFCLASS64:
+ return 64;
+ default:
+ errx(1, "Unknown machine word size.");
+ }
+}
+
+int
+get_endian(uint8_t ei_data)
+{
+ switch (ei_data) {
+ case ELFDATA2LSB:
+ return 0;
+ case ELFDATA2MSB:
+ return 1;
+ default:
+ errx(1, "Unknown endian.");
+ }
+}
+
char *
get_abi(uint16_t e_machine, int width, uint32_t e_flags)
@@ -117,7 +140,7 @@ get_abi(uint16_t e_machine, int width, uint32_t e_flags)
return "arm_64";
/* m68k: We support only one 32-bit ABI. */
- case EM_68K_BE:
+ case EM_68K:
return "m68k_32";
/* mips: We support o32, n32 and n64. The first is 32-bits and
the
@@ -132,33 +155,25 @@ get_abi(uint16_t e_machine, int width, uint32_t e_flags)
else
return "mips_o32";
- case EM_MIPS_BE:
- if (width == 64)
- return "mips_n64";
- else
- if (e_flags & EF_MIPS_ABI2_BE)
- return "mips_n32";
- else
- return "mips_o32";
/* ia64: We support only one 64-bit ABI. */
case EM_IA_64:
return "ia_64";
/* hppa: We support only one 32-bit ABI. */
- case EM_PARISC_BE:
+ case EM_PARISC:
return "hppa_32";
/* ppc: We support only one 32-bit ABI. */
- case EM_PPC_BE:
+ case EM_PPC:
return "ppc_32";
/* ppc64: We support only one 64-bit ABI. */
- case EM_PPC64_BE:
+ case EM_PPC64:
return "ppc_64";
/* s390: We support one 32-bit and one 64-bit ABI. */
- case EM_S390_BE:
+ case EM_S390:
if (width == 64)
return "s390_64";
else
@@ -169,9 +184,9 @@ get_abi(uint16_t e_machine, int width, uint32_t e_flags)
return "sh_32";
/* sparc: We support one 32-bit and one 64-bit ABI. */
- case EM_SPARC32_BE:
+ case EM_SPARC32PLUS:
return "sparc_32";
- case EM_SPARC64_BE:
+ case EM_SPARCV9:
return "sparc_64";
/* amd64 + x86: We support X86-64, X86-X32, and X86-32 ABI. The
first
@@ -192,16 +207,42 @@ get_abi(uint16_t e_machine, int width, uint32_t e_flags)
}
+/* Sublte point about read(): If you run elf-abi from a little endian machine
on an */
+/* Elf object on a big endian (eg. if you are cross compiling), then you get
the wrong */
+/* byte order. If howerver, you read it natively, you get it right. We'll
wrap read() */
+/* with our own version which reads one byte at a time and corrects this.
*/
+ssize_t
+read_endian(int fd, void *buf, size_t count, int endian)
+{
+ ssize_t i;
+ uint8_t data;
+
+ for(i = 0; i < count; i++) {
+ if (read(fd, &data, 1) == -1)
+ errx(1, "read() ei_class failed");
+ if (endian)
+ ((uint8_t *)buf)[count-i-1] = data;
+ else
+ ((uint8_t *)buf)[i] = data;
+ }
+
+ return count;
+}
+
+
int
main(int argc, char* argv[])
{
int width; /* Machine word size. Either 32 or 64
bits. */
+ int endian; /* Endian, 0 = little, 1 = big
*/
char *abi; /* Abi name from glibc's
<bits/syscall.h> */
int fd; /* file descriptor for opened Elf
object. */
struct stat s; /* stat on opened Elf object.
*/
char magic[4]; /* magic number at the begining of the
file */
uint8_t ei_class; /* ei_class is one byte of e_ident[]
*/
+ uint8_t ei_data; /* ei_data is one byte of e_ident[]
*/
+
uint16_t e_machine; /* Size is Elf32_Half or Elf64_Half.
Both are 2 bytes. */
uint32_t e_flags; /* Size is Elf32_Word or Elf64_Word.
Both are 4 bytes. */
uint64_t e_machine_offset, e_flags_offset; /* Wide enough for either
32 or 64 bits. */
@@ -216,25 +257,21 @@ main(int argc, char* argv[])
/* Can we read it and is it an ELF object? */
if ((fd = open(argv[1], O_RDONLY)) == -1)
- err(1, "failed to open %s", argv[1]);
+ errx(1, "failed to open %s", argv[1]);
if (read(fd, magic, 4) == -1)
- err(1, "read() magic failed");
+ errx(1, "read() magic failed");
if (strncmp(magic, ELFMAG, 4) != 0)
errx(1, "%s is not an ELF object", argv[1]);
/* 32 or 64 bits machine word size? */
if (read(fd, &ei_class, 1) == -1)
- err(1, "read() ei_class failed");
- switch (ei_class) {
- case ELFCLASS32:
- width = 32;
- break;
- case ELFCLASS64:
- width = 64;
- break;
- default:
- errx(1, "Unknown machine word size.");
- }
+ errx(1, "read() ei_class failed");
+ width = get_wordsize(ei_class);
+
+ /* Little or Big Endian? */
+ if (read(fd, &ei_data, 1) == -1)
+ errx(1, "read() ei_data failed");
+ endian = get_endian(ei_data);
/*
All Elf files begin with the following Elf header:
@@ -258,14 +295,12 @@ main(int argc, char* argv[])
/* What is the abi? */
if (lseek(fd, e_machine_offset, SEEK_SET) == -1)
- err(1, "lseek() e_machine failed");
- if (read(fd, &e_machine, 2) == -1)
- err(1, "read() e_machine failed");
+ errx(1, "lseek() e_machine failed");
+ read_endian(fd, &e_machine, 2, endian);
if (lseek(fd, e_flags_offset, SEEK_SET) == -1)
- err(1, "lseek() e_flags failed");
- if (read(fd, &e_flags, 4) == -1)
- err(1, "read() e_flags failed");
+ errx(1, "lseek() e_flags failed");
+ read_endian(fd, &e_flags, 4, endian);
abi = get_abi(e_machine, width, e_flags);
printf("%s\n", abi);
