elfinspect

Commit: a42d40b02ffe7269c267c5bb0e9e46986e65bc76
Parent: 4b47bf2622fd0e8a62f5d59f8c05c1250b8b16c6
Author: Randy Palamar
Date:   Sun, 27 Apr 2025 09:43:01 -0600

elf header dumping

Diffstat:
A
build.sh
 | 
3
+++
A
elfinspect.c
 | 
135
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
A
main_posix.c
 | 
45
+++++++++++++++++++++++++++++++++++++++++++++

3 files changed, 183 insertions(+), 0 deletions(-)
diff --git a/build.sh b/build.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+clang -march=native -O0 -ggdb main_posix.c -o elfinspect
diff --git a/elfinspect.c b/elfinspect.c
@@ -0,0 +1,135 @@
+#define local_persist static
+#define global        static
+#define function      static
+
+/* TODO(rnp) platform specific */
+#define ASSERT(c) do { if (!(c)) asm("int3"); } while (0)
+
+#define countof(a) (sizeof(a) / sizeof(*a))
+
+typedef struct {u8 *beg, *end;} Arena;
+
+#define str8(s) (str8){.len = countof(s) - 1, .data = (u8 *)s}
+typedef struct { iz len; u8 *data;} str8;
+
+/* NOTE: platform api; defined here so that other platform symbols are not visible to this TU */
+function str8 os_map_file(u8 *);
+
+/* X(ctype, name) */
+#define ELF_HEADER_MEMBERS(ptrsize) \
+	X(u16,     type)      \
+	X(u16,     machine)   \
+	X(u32,     version)   \
+	X(ptrsize, entry)     \
+	X(ptrsize, phoff)     \
+	X(ptrsize, shoff)     \
+	X(u32,     flags)     \
+	X(u16,     ehsize)    \
+	X(u16,     phentsize) \
+	X(u16,     phnum)     \
+	X(u16,     shentsize) \
+	X(u16,     shnum)     \
+	X(u16,     shstrndx)
+
+#define X(ctype, name) ctype name;
+typedef struct { u8 identifier[16]; ELF_HEADER_MEMBERS(u32) } ELFHeader32;
+typedef struct { u8 identifier[16]; ELF_HEADER_MEMBERS(u64) } ELFHeader64;
+#undef X
+
+typedef enum {
+	EHK_NONE = 0x00,
+	EHK_32   = 0x01,
+	EHK_64   = 0x02,
+} ELFHeaderKind;
+
+typedef struct {
+	union {
+		ELFHeader64 eh64;
+		ELFHeader32 eh32;
+	} u;
+	ELFHeaderKind kind;
+} ELFHeader;
+
+typedef enum {
+	EEK_NONE   = 0x00,
+	EEK_LITTLE = 0x01,
+	EEK_BIG    = 0x02,
+} ELFEndianKind;
+
+function void
+print_u64(u64 v)
+{
+	printf("%zu", v);
+}
+
+function void print_u16(u16 v) { print_u64(v); }
+function void print_u32(u32 v) { print_u64(v); }
+
+function void
+print_elf_header_32(ELFHeader *eh)
+{
+	ASSERT(eh->kind == EHK_32);
+	printf("TODO: print 32 bit elf header\n");
+}
+
+function void
+print_elf_header_64(ELFHeader *eh)
+{
+	ASSERT(eh->kind == EHK_64);
+	printf("ELF Header:\nidentifier: 0x");
+	for (u32 i = 0; i < countof(eh->u.eh64.identifier); i++)
+		printf(" %02x", eh->u.eh64.identifier[i]);
+	#define X(ctype, name) printf("\n"); printf(#name ": "); print_##ctype(eh->u.eh64.name);
+	ELF_HEADER_MEMBERS(u64)
+	#undef X
+	printf("\n");
+}
+
+function void
+print_elf_header(ELFHeader *eh)
+{
+	switch (eh->kind) {
+	case EHK_32: print_elf_header_32(eh);    break;
+	case EHK_64: print_elf_header_64(eh);    break;
+	default: printf("invalid elf header\n"); break;
+	}
+}
+
+function b32
+is_elf(str8 file)
+{
+	b32 result = file.len >= 16;
+	result &= file.data[0] == 0x7F;
+	result &= file.data[1] == 'E';
+	result &= file.data[2] == 'L';
+	result &= file.data[3] == 'F';
+	return result;
+}
+
+function ELFHeader
+elf_header_from_file(str8 file)
+{
+	ELFHeader result = {0};
+	ASSERT(file.len > sizeof(ELFHeader64));
+	ASSERT(file.data[4] == EHK_64);
+	ASSERT(file.data[5] == EEK_LITTLE);
+
+	result.u.eh64 = *(ELFHeader64 *)file.data;
+	result.kind   = file.data[4];
+
+	return result;
+}
+
+function b32
+elfinspect(str8 file)
+{
+	b32 result = 0;
+
+	if (is_elf(file)) {
+		ELFHeader header = elf_header_from_file(file);
+		print_elf_header(&header);
+		result = 1;
+	}
+
+	return result;
+}
diff --git a/main_posix.c b/main_posix.c
@@ -0,0 +1,45 @@
+#include <stdint.h>
+#include <stddef.h>
+
+typedef uint8_t    u8;
+typedef uint16_t  u16;
+typedef uint32_t  u32;
+typedef uint32_t  b32;
+typedef uint64_t  u64;
+typedef int8_t     s8;
+typedef int16_t   s16;
+typedef int32_t   s32;
+typedef int64_t   s64;
+typedef ptrdiff_t  iz;
+
+#include <stdio.h>
+
+#include "elfinspect.c"
+
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+function str8
+os_map_file(u8 *name)
+{
+	str8 result = {0};
+	s32 fd = open((char *)name, O_RDONLY);
+	struct stat sb;
+	if (fd != -1 && fstat(fd, &sb) != -1) {
+		result.data = mmap(0, sb.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+		if (result.data != MAP_FAILED)
+			result.len = sb.st_size;
+	}
+	if (fd != -1) close(fd);
+	return result;
+}
+
+s32
+main(s32 argc, char *argv[])
+{
+	str8 file = os_map_file((u8 *)argv[0]);
+	elfinspect(file);
+	return 0;
+}