From 29a8eebf9231692f965f29221d140e20b0a1f64b Mon Sep 17 00:00:00 2001
From: Regia König
Date: Wed, 24 Aug 2022 14:28:23 +0200
Subject: Analyse memtest86 binary structure

---
 .../24_08_22_memtest_build_process                 | 205 +++++++++++++++++++++
 1 file changed, 205 insertions(+)
 create mode 100644 documentation/memtest86_build_process/24_08_22_memtest_build_process

diff --git a/documentation/memtest86_build_process/24_08_22_memtest_build_process b/documentation/memtest86_build_process/24_08_22_memtest_build_process
new file mode 100644
index 0000000..9847a5b
--- /dev/null
+++ b/documentation/memtest86_build_process/24_08_22_memtest_build_process
@@ -0,0 +1,205 @@
+
+Linker scripts: 
+	memtest_shared.lds
+	memtest_efi.lds
+boot/
+	header.S			|| The standard EFI header
+	setup.S
+	efisetup.c			|| Macros + private functions 
+					|| Only for 32-bit boot entry point???
+	startup64.S
+
+*.c files in app/, lib/, system/, tests/
+
+##########################################################################
+##									##
+##		MEMTEST LINKING PART 1 - MEMTEST_SHARED			##
+##									##
+##########################################################################
+
+#
+#	memtest_shared.lds
+#
+
+OUTPUT_FORMAT("elf64-x86-64")
+
+ENTRY(startup64);   <--------- in startup64.S
+
+SECTIONS {
+	.text : {
+		_start = .;  <---------- First section in memtest_shared-.text
+		*(.text)
+		*(.text.*)
+		...
+
+	.rodata
+	.dynsym
+	.dynstr
+	.hash
+	.gnu.hash
+	.dynamic
+
+	.rela.text
+	.rela.rodata
+	.rela.data
+	.rela.got
+	.rela.plt
+
+	.data
+	.got
+	.bss
+
+#
+#	startup64.S
+#
+118:	.globl startup64
+119:	startup64:
+120:		cld
+121:		cli
+
+		# Save the boot params pointer
+125:		movq	%rsi, boot_params_addr(%rip)
+
+127:		jmp startup
+
+143:	.globl	startup
+144:	startup:
+		Use startup stack until we pick a correct one
+		Pick the correct stack
+		Initialize the pml4 and pdp tables
+		Set the page directory base address
+		Initialise the GDT and the segment registers
+		Load the GDT and the segment registers
+		Initialise the IDT
+		Initialise the IDT descriptor
+		Zero the BSS (if first boot)
+		Initialise the FPU
+		Enable SSE
+		Call the dynamic linker to fix up the addresses in the GOT
+
+268:	call reloc  <---------------- system/reloc64.c:151
+		get_load_address()
+		get_dynamic_section_offset()
+		get_dynamic_info()
+		do_relocations
+
+276:	call main  <---------------- app/main.c:499  # main entry point called from the startup code
+
+#
+# Analysis of the binary
+#
+
+* objdump -h memtest_shared
+	.text	...	File off	Algn
+			00200000	2**4
+
+* objdump -g memtest_shared | grep efi_setup		# check for occurences
+			    | grep efi_handover	
+
+* readelf -h memtest_shared
+	ELF Header:
+	  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
+	  Class:                             ELF64
+	  Data:                              2's complement, little endian
+	  Version:                           1 (current)
+	  OS/ABI:                            UNIX - System V
+	  ABI Version:                       0
+	  Type:                              DYN (Shared object file)
+	  Machine:                           Advanced Micro Devices X86-64
+	  Version:                           0x1
+	  Entry point address:               0x200  <-----------------That's startup64 !!!
+	  Start of program headers:          64 (bytes into file)
+	  Start of section headers:          2821656 (bytes into file)
+	  Flags:                             0x0
+	  Size of this header:               64 (bytes)
+	  Size of program headers:           56 (bytes)
+	  Number of program headers:         3
+	  Size of section headers:           64 (bytes)
+	  Number of section headers:         26
+	  Section header string table index: 25
+
+* objdump -d memtest_shared
+	memtest_shared: file format elf64-x86-64
+
+	Disassembly of section .text:
+
+	0000000000000000 <_start>:
+	0:	cld
+	1:	cli
+
+	9f:	ljmp	*-0x6(%rsp)
+
+	00000000000001e0 <efi_boot>:
+	
+	1ed:	jmp 210 <efi_handover>
+
+	0000000000000200 <startup64>:
+
+	202:	mov %rsi,0x23df7(%rip)		# 2400 <boot_params_addr>
+	209:	jmp 220 <startup>
+
+	0000000000000210 <efi_handover>:
+
+	214:	callq 68f <efi_setup>
+	219:	mov %rax,0x23de0(%rip)		# 2400 <boot_params_addr> 
+
+	0000000000000220 <startup>:
+
+	2ce:	ljmp *-0x6(%rsp)
+
+
+
+##########################################################################
+##									##
+##		MEMTEST LINKING PART 2 - MEMTEST.EFI			##
+##									##
+##########################################################################
+
+#
+#	memtest_efi.lds
+#
+OUTPUT_FORMAT("binary")
+
+ENTRY(boot);			<----- in boot/header.S:36
+
+SECTIONS {
+	.header : {		<----- boot/header.S
+		*(.header)
+	}
+	.setup : {		<----- boot/setup.S
+		*(.setup)
+	}
+	.text : {
+		_text_start = .;
+		*(.data)	<----- !!! NO .text !!!!
+		...
+
+#
+#	header.S
+#
+The EFI loader loads the header at ImageBase, so we have to locate the main program
+after that. This means we can't load the main program at HIGH_LOAD_ADDR. Pick a load
+address well away from HIGH_LOAD_ADDR, to avoid overlap when relocating code.
+
+. # define IMAGE_BASE	0x200000
+. # define BASE_OF_CODE	0x1000		<- where do these values come from?????
+
+	.section ".header", "ax", @progbits
+	.code16
+
+	.globl boot
+
+boot:
+	"MZ", the MS-DOS header signature
+	.byte 0x4d
+	.byte 0x5a
+
+pe_header:
+
+coff_header:
+
+...
+
+#
+#	setup.S
+#
-- 
cgit v1.2.3-55-g7522