From f94a0dcba4dfd31f511a286f95197ee3610edb21 Mon Sep 17 00:00:00 2001
From: Garritt McCune <glmccune@gmail.com>
Date: Mon, 22 Apr 2024 20:42:58 -0500
Subject: [PATCH] Finished writing the code to parse out the ELF header into a
 structure.

---
 elf_header.c | 107 +++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 86 insertions(+), 21 deletions(-)

diff --git a/elf_header.c b/elf_header.c
index a854a03..a4a826e 100644
--- a/elf_header.c
+++ b/elf_header.c
@@ -11,6 +11,11 @@
 #define ELF_BYTE_ORDER_LSB 1
 #define ELF_BYTE_ORDER_MSB 2
 
+#define ELF64_ADDR_SIZE sizeof(uint64_t)
+#define ELF64_OFFSET_SIZE ELF64_ADDR_SIZE
+#define ELF64_WORD_SIZE ELF64_ADDR_SIZE / 2
+#define ELF64_HALF_SIZE ELF64_WORD_SIZE / 2
+
 typedef enum EIdent
 {
 	EI_MAG0 = 0, //Magic number position zero - three.
@@ -24,10 +29,6 @@ typedef enum EIdent
 	EI_ABIVERSION = ELF_OSABI_VERSION_IDENT_INDEX,
 	EI_PAD = 9,
 	EI_NIDENT = ELF_IDENTITIFCATION_MAX_SIZE - 1, //End of reserved 16 bytes for the header.
-	EI_TYPE = EI_NIDENT + 1,
-	EI_MACHINE = EI_TYPE + 2,
-	EI_OBJECT_FILE_VERSION = EI_MACHINE + 2,
-	EI_ENTRY_ADDRESS_POINT = EI_OBJECT_FILE_VERSION + 4
 } ELFIdentOffsets;
 
 struct elf_header {
@@ -39,6 +40,12 @@ struct elf_header {
 	uint64_t ProgramHeaderOffset;
 	uint64_t SectionHeaderOffset;
 	uint32_t Flags;
+	uint16_t HeaderSize;
+	uint16_t ProgramHeaderEntrySize;
+	uint16_t ProgramHeaderEntryCount;
+	uint16_t SectionHeaderEntrySize;
+	uint16_t SectionHeaderEntryCount;
+	uint16_t SectionNamesIndex;
 };
 
 struct elf_header* CreateELFHeader(void);
@@ -61,17 +68,60 @@ struct elf_header* ParseObjectFile(const char* bytes, size_t count) {
 		return NULL;
 	}
 
-	switch(bytes[EI_CLASS])
-	{
-		case ELF_CLASS_TYPE32:
-			memcpy(&header->EntryAddress, &bytes[EI_ENTRY_ADDRESS_POINT], sizeof(int32_t));
-			break;
-		case ELF_CLASS_TYPE64:
-			memcpy(&header->EntryAddress, &bytes[EI_ENTRY_ADDRESS_POINT], sizeof(int64_t));
-			break;
-		default:
-			header->EntryAddress = -1;
-	}
+	uint64_t offsetSize = header->Identitication[EI_CLASS] == ELF_CLASS_TYPE32 ? ELF64_OFFSET_SIZE / 2 : ELF64_OFFSET_SIZE;
+	uint64_t wordSize = ELF64_WORD_SIZE;//header->Identitication[EI_CLASS] == ELF_CLASS_TYPE32 ? ELF64_WORD_SIZE / 2 : ELF64_WORD_SIZE;
+	uint64_t halfSize = ELF64_HALF_SIZE;//header->Identitication[EI_CLASS] == ELF_CLASS_TYPE32 ? ELF64_HALF_SIZE / 2 : ELF64_HALF_SIZE;
+	size_t cursor = ELF_IDENTITIFCATION_MAX_SIZE;
+	
+	memcpy(&header->FileType, &bytes[cursor], halfSize); //e_type
+
+	cursor += halfSize;
+
+	memcpy(&header->ISA, &bytes[cursor], halfSize); //e_machine
+
+	cursor += halfSize;
+
+	memcpy(&header->ELFVersion, &bytes[cursor], wordSize); //e_version
+
+	cursor += wordSize;
+
+	memcpy(&header->EntryAddress, &bytes[cursor], offsetSize); //e_entry
+
+	cursor += offsetSize;
+
+	memcpy(&header->ProgramHeaderOffset, &bytes[cursor], offsetSize); //e_phoff
+
+	cursor += offsetSize;
+
+	memcpy(&header->SectionHeaderOffset, &bytes[cursor], offsetSize); //e_shoff
+
+	cursor += offsetSize;
+
+	memcpy(&header->Flags, &bytes[cursor], wordSize); //e_flags
+
+	cursor += wordSize;
+
+	memcpy(&header->HeaderSize, &bytes[cursor], halfSize); //e_ehsize
+
+	cursor += halfSize;
+
+	memcpy(&header->ProgramHeaderEntrySize, &bytes[cursor], halfSize); //e_phentsize
+
+	cursor += halfSize;
+
+	memcpy(&header->ProgramHeaderEntryCount, &bytes[cursor], halfSize); //e_phnum
+
+	cursor += halfSize;
+
+	memcpy(&header->SectionHeaderEntrySize, &bytes[cursor], halfSize); //e_shentsize
+
+	cursor += halfSize;
+
+	memcpy(&header->SectionHeaderEntryCount, &bytes[cursor], halfSize); //e_shnum
+
+	cursor += halfSize;
+
+	memcpy(&header->SectionNamesIndex, &bytes[cursor], halfSize); //e_shstrndx
 
 	switch(bytes[EI_DATA])
 	{
@@ -94,16 +144,31 @@ struct elf_header* ParseObjectFile(const char* bytes, size_t count) {
 
 	printf("OS ABI: %s\n", buffer);
 
-	GetELFMachineTypeText(bytes[EI_MACHINE], buffer);
+	GetELFMachineTypeText((ELFMachine)header->ISA, buffer);
 
 	printf("Machine type: %s\n", buffer);
-	printf("Machine: %d\n", bytes[EI_MACHINE]);
 
-	// int64_t entryAddress;
+	printf("Object File Version: %#02x\n", header->ELFVersion);
 
-	// memcpy(&entryAddress, &bytes[EI_ENTRY_ADDRESS_POINT], sizeof(int64_t));
+	printf("Entry point address: %#06lx\n", header->EntryAddress);
 
-	// printf("Entry point address: %#06lx\n", entryAddress);
+	printf("Program Header Offset: %ld bytes\n", header->ProgramHeaderOffset);
+
+	printf("Section Header Offset: %ld bytes\n", header->SectionHeaderOffset);
+
+	printf("Flags: %#04x\n", header->Flags);
+
+	printf("Size of Header: %d bytes\n", header->HeaderSize);
+
+	printf("Size of Program Headers: %d bytes\n", header->ProgramHeaderEntrySize);
+
+	printf("Number of Programer Headers: %d\n", header->ProgramHeaderEntryCount);
+
+	printf("Size of Section Header: %d bytes\n", header->SectionHeaderEntrySize);
+
+	printf("Number of Section Headers: %d\n", header->SectionHeaderEntryCount);
+
+	printf("Section Header string table index: %d\n", header->SectionNamesIndex);
 	
     return header;
 }
@@ -121,7 +186,7 @@ void ELFPrintMagic(const struct elf_header* header) {
 
     for(int i = 0; i < ELF_IDENTITIFCATION_MAX_SIZE; i++)
 	{
-		printf("%02X ", header->Identitication[i]);
+		printf("%02x ", header->Identitication[i]);
 	}
 
 	printf("\n");