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Separate out ELF header parsing to another file

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This commit is contained in:
Curle 2020-12-02 02:33:59 +00:00
parent 986c7816b1
commit c843c418ad
Signed by: TheCurle
GPG Key ID: 5942F13718443F79
4 changed files with 119 additions and 62 deletions
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1
CMakeLists.txt
View File

@ -24,6 +24,7 @@ SET(src_files
${CMAKE_SOURCE_DIR}/chroma/system/memory/abstract_allocator.c
${CMAKE_SOURCE_DIR}/chroma/system/memory/physmem.c
${CMAKE_SOURCE_DIR}/chroma/system/drivers/keyboard.c
${CMAKE_SOURCE_DIR}/chroma/system/drivers/elf.c
)
SET(lib_files

48
chroma/inc/kernel/boot/boot.h
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@ -11,6 +11,30 @@
extern "C" {
#endif
/* ELF headers hate me.
* Let's do this the hard way. */
#define ELF_IDENT_MAGIC_OFF 0x0
#define ELF_IDENT_CLASS_OFF 0x4
#define ELF_IDENT_DATA_OFF 0x5
#define ELF_IDENT_VERSION_OFF 0x6
#define ELF_IDENT_OSABI_OFF 0x7
#define ELF_IDENT_ABI_VERSION_OFF 0x8
#define ELF_IDENT_PAD_OFF 0x9
#define ELFTYPE_OFF 0x10
#define ELFMACHINE_OFF 0x12
#define ELFVERSION_OFF 0x14
#define ELFENTRY_OFF 0x18
#define ELFPHOFF_OFF 0x20
#define ELFSHOFF_OFF 0x28
#define ELFFLAGS_OFF 0x30
#define ELFEHSIZE_OFF 0x34
#define ELFPHENTSIZE_OFF 0x36
#define ELFPHNUM_OFF 0x38
#define ELFSHENTSIZE_OFF 0x3A
#define ELFSHNUM_OFF 0x3C
#define ELFSHSTRNDX_OFF 0x40
#define BOOT_MAGIC "BOOT"
/* minimum protocol level:
@ -108,30 +132,6 @@ typedef struct {
} __attribute__((packed)) bootinfo;
typedef struct {
uint32_t Magic;
uint8_t Class;
uint8_t Endianness;
uint8_t Version;
uint8_t ABI;
uint8_t ABIVersion;
uint8_t Unused[7];
uint16_t Type;
uint16_t TargetArchitecture;
uint32_t ELFVersion;
size_t EntryPoint;
size_t ProgramHeadersTable;
size_t SectionHeadersTable;
uint32_t Flags;
uint16_t ELFHeaderSize;
uint16_t ProgramHeadersEntrySize;
uint16_t ProgramHeaderEntries;
uint16_t SectionHeadersEntrySize;
uint16_t SectionHeaderEntries;
uint16_t SectionHeaderNameEntry;
uint8_t End;
} __attribute__((packed)) ELF64Header_t;
#ifdef __cplusplus
}

41
chroma/kernel.c
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@ -20,48 +20,13 @@ address_space_t KernelAddressSpace;
int Main(void) {
KernelAddressSpace = (address_space_t) {0};
KernelLocation = 0x112600;
SerialPrintf("\r\n[ boot] Booting Chroma..\r\n");
SerialPrintf("[ boot] Kernel loaded at 0x%p, ends at 0x%p, is %d bytes long.\r\n", KernelAddr, KernelEnd, KernelEnd - KernelAddr);
SerialPrintf("[ boot] Initrd is physically at 0x%p, and is %d bytes long.\r\n", bootldr.initrd_ptr, bootldr.initrd_size);
SerialPrintf("[ boot] Searching for kernel... Constants start at 0x%p\r\n", &_kernel_text_start);
// We stop at the constants in the kernel, otherwise we'll read the constant ELF64MAGIC which is stored inside the kernel...
size_t headerLoc = 0;
for(size_t i = KernelAddr; i < KernelEnd; i++) {
if(i < (size_t) (&_kernel_text_start) - KernelAddr) {
if(*((volatile uint32_t*)(i)) == ELF64MAGIC) {
SerialPrintf("[ boot] Matched kernel header at 0x%p.\r\n", i);
}
}
}
int flag = 0;
if(headerLoc) {
ELF64Header_t* PotentialKernelHeader = (ELF64Header_t*) &headerLoc;
SerialPrintf(
"[ boot] Considering ELF with:\r\n\tBitness %d\r\n\tEntry point 0x%p\r\n\tFile type %s : %d\r\n\tArchitecture %s : %d\r\n",
PotentialKernelHeader->Class == 2 ? 64 : 32, PotentialKernelHeader->EntryPoint, PotentialKernelHeader->Type == 0x02 ? "EXECUTABLE" : "OTHER", PotentialKernelHeader->Type, PotentialKernelHeader->TargetArchitecture == 0x3E ? "AMD64" : "OTHER", PotentialKernelHeader->TargetArchitecture);
if(PotentialKernelHeader->EntryPoint == KernelAddr) {
SerialPrintf("[ boot] Header at 0x%p matches kernel header.\r\n", headerLoc);
flag = 1;
}
if(!flag) {
for(size_t i = 0; i < 8; i++) {
SerialPrintf("[ boot] Header dump part %d: 0x%x\r\n", i, *((volatile uint32_t*)(headerLoc + i)));
}
}
}
if(!flag) {
SerialPrintf("[ boot] Unable to find kernel in memory. Fatal error.\r\n");
//for(;;) {}
}
SerialPrintf("[ boot] Initrd's header is 0x%p\r\n", FIXENDIAN32(*((volatile uint32_t*)(bootldr.initrd_ptr))));
ParseKernelHeader(bootldr.initrd_ptr);
SerialPrintf("[ boot] The bootloader has put the paging tables at 0x%p.\r\n", ReadControlRegister(3));

91
chroma/system/drivers/elf.c Normal file
View File

@ -0,0 +1,91 @@
#include <kernel/chroma.h>
/************************
*** Team Kitty, 2020 ***
*** Chroma ***
***********************/
/*
* This file provides utility functions for parsing ELF headers.
* This exists so that the kernel can find itself for remapping,
* but I may end up using ELF as the kernel's executable format.
* Writing an ELF loader is on the to-do list, after all.
! This needs to be cleaned up.
! This creates a mess of numbers on the print
! This is hacky and hardcoded as heck and needs to be fixed
*/
extern size_t KernelLocation;
int ParseKernelHeader(size_t InitrdPtr) {
int flag = 0;
SerialPrintf("[ boot] Searching for kernel... Constants start at 0x%p / 0x%p\r\n", ((size_t) (&_kernel_text_start) - KernelAddr) + InitrdPtr, (size_t) (&_kernel_text_start));
// We stop at the constants in the kernel, otherwise we'll read the constant ELF64MAGIC which is stored inside the kernel...
size_t headerLoc = 0;
for(size_t i = InitrdPtr; i < ((size_t) (&_kernel_text_start) - KernelAddr) + InitrdPtr; i++) {
if(*((volatile uint32_t*)(i)) == ELF64MAGIC) {
SerialPrintf("[ boot] Matched kernel header at 0x%p.\r\n", i);
headerLoc = i;
}
if(FIXENDIAN32(*((volatile uint32_t*)(i))) == ELF64MAGIC) {
SerialPrintf("[ boot] Matched little-endian kernel header at 0x%p.\r\n", i);
headerLoc = i;
}
}
if(headerLoc) {
/* For whatever reason, reading a size_t here fails. The max that seems to work is uint16_t, so we read in the
* 64 bit address by constructing it from 4 individual reads.
* Note that these 4 reads are little endian, so we need to flip them around individually
*/
uint16_t EntryPoint0 = FIXENDIAN16(*((volatile uint16_t*)(headerLoc + ELFENTRY_OFF)));
uint16_t EntryPoint1 = FIXENDIAN16(*((volatile uint16_t*)(headerLoc + ELFENTRY_OFF + 2)));
uint16_t EntryPoint2 = FIXENDIAN16(*((volatile uint16_t*)(headerLoc + ELFENTRY_OFF + 4)));
uint16_t EntryPoint3 = FIXENDIAN16(*((volatile uint16_t*)(headerLoc + ELFENTRY_OFF + 6)));
size_t EntryPoint = ((size_t) EntryPoint0 << 48) | ((size_t) EntryPoint1 << 32) | ((size_t) EntryPoint2 << 16) | ((size_t) EntryPoint3);
/* At this point, EntryPoint is a little-endian 64 bit integer. That means we have to fix its endianness in order to read it */
SerialPrintf("[ boot] Fixing entry point from 0x%p to 0x%p\r\n", EntryPoint, FIXENDIAN64(EntryPoint));
EntryPoint = FIXENDIAN64(EntryPoint);
/* Now we can continue as normal */
uint8_t HeaderClass = *((volatile uint8_t*)(headerLoc + ELF_IDENT_CLASS_OFF));
uint16_t ExecutableType = (uint16_t) *((volatile uint8_t*)(headerLoc + ELFTYPE_OFF));
uint16_t MachineType = (uint16_t) *((volatile uint8_t*)(headerLoc + ELFMACHINE_OFF));
SerialPrintf(
"[ boot] ELF header at 0x%p.\r\n\tConsidering ELF with:\r\n\tBitness %d: %d\r\n\tEntry point 0x%p\r\n\tFile type %s : 0x%x\r\n\tArchitecture %s : 0x%x\r\n",
headerLoc,
HeaderClass == 2 ? 64 : 32,
HeaderClass,
EntryPoint,
ExecutableType == FIXENDIAN16(0x0200) ? "EXECUTABLE" : "OTHER",
FIXENDIAN16(ExecutableType),
MachineType == FIXENDIAN16(0x3E00) ? "AMD64" : "OTHER",
FIXENDIAN16(MachineType));
if(EntryPoint == (size_t) (&_kernel_text_start)) {
SerialPrintf("[ boot] Header at 0x%p matches kernel header.\r\n", headerLoc);
flag = 1;
// At this point, we've found the right ELF64 executable!
// Great, now we can map it into the proper place
KernelLocation = headerLoc;
}
if(!flag) {
for(char i = 0; i < 64; i++) {
SerialPrintf("[ boot] Header dump part %x: 0x%x\r\n", i, *((volatile uint8_t*)(headerLoc + i)));
}
}
}
return flag;
}