From 1a48bec601a02ad8d7e821cab29e813fd90ab710 Mon Sep 17 00:00:00 2001
From: mintsuki <mintsuki@protonmail.com>
Date: Wed, 25 Mar 2020 01:04:18 +0100
Subject: [PATCH] Add elf parser

---
 Makefile      |  3 +-
 src/lib/elf.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++
 src/lib/elf.h |  8 +++++
 src/main.c    |  1 +
 test/Makefile |  2 +-
 test/test.asm |  4 ++-
 6 files changed, 104 insertions(+), 3 deletions(-)
 create mode 100644 src/lib/elf.c
 create mode 100644 src/lib/elf.h

diff --git a/Makefile b/Makefile
index a6e5be1f..a31b7889 100644
--- a/Makefile
+++ b/Makefile
@@ -8,6 +8,7 @@ clean:
 
 test:
 	$(MAKE) -C test
+	rm -f test.img
 	dd if=/dev/zero bs=1M count=0 seek=64 of=test.img
 	parted -s test.img mklabel msdos
 	parted -s test.img mkpart primary 1 100%
@@ -15,4 +16,4 @@ test:
 	echfs-utils -m -p0 test.img import test/test.elf test.elf
 	echfs-utils -m -p0 test.img import test/qloader2.cfg qloader2.cfg
 	./qloader2-install test.img
-	qemu-system-x86_64 -hda test.img
+	qemu-system-x86_64 -hda test.img -monitor stdio
diff --git a/src/lib/elf.c b/src/lib/elf.c
new file mode 100644
index 00000000..71e3be6b
--- /dev/null
+++ b/src/lib/elf.c
@@ -0,0 +1,89 @@
+#include <stdint.h>
+#include <stddef.h>
+#include <lib/blib.h>
+#include <lib/libc.h>
+#include <lib/elf.h>
+
+#define PT_LOAD     0x00000001
+#define PT_INTERP   0x00000003
+#define PT_PHDR     0x00000006
+
+#define ABI_SYSV 0x00
+#define ARCH_X86_64 0x3e
+#define BITS_LE 0x01
+
+/* Indices into identification array */
+#define	EI_CLASS	4
+#define	EI_DATA		5
+#define	EI_VERSION	6
+#define	EI_OSABI	7
+
+struct elf_hdr {
+    uint8_t ident[16];
+    uint16_t type;
+    uint16_t machine;
+    uint32_t version;
+    uint32_t entry;
+    uint32_t phoff;
+    uint32_t shoff;
+    uint32_t flags;
+    uint16_t hdr_size;
+    uint16_t phdr_size;
+    uint16_t ph_num;
+    uint16_t shdr_size;
+    uint16_t sh_num;
+    uint16_t shstrndx;
+};
+
+struct elf_phdr {
+    uint32_t p_type;
+    uint32_t p_offset;
+    uint32_t p_vaddr;
+    uint32_t p_paddr;
+    uint32_t p_filesz;
+    uint32_t p_memsz;
+    uint32_t p_flags;
+};
+
+int echfs_read(struct echfs_file_handle *file, void *buf, uint64_t loc, uint64_t count);
+
+int elf_load(struct echfs_file_handle *fd) {
+    struct elf_hdr hdr;
+    echfs_read(fd, &hdr, 0, sizeof(struct elf_hdr));
+
+    if (strncmp((char *)hdr.ident, "\177ELF", 4)) {
+        print("Not a valid ELF file.\n");
+        return 1;
+    }
+
+    if (hdr.ident[EI_DATA] != BITS_LE) {
+        print("Not a Little-endian ELF file.\n");
+        return -1;
+    }
+
+    for (uint16_t i = 0; i < hdr.ph_num; i++) {
+        struct elf_phdr phdr;
+        echfs_read(fd, &phdr, hdr.phoff + i * sizeof(struct elf_phdr),
+                   sizeof(struct elf_phdr));
+
+        if (phdr.p_type != PT_LOAD)
+            continue;
+
+
+        echfs_read(fd, (void *)phdr.p_vaddr, phdr.p_offset, phdr.p_filesz);
+
+        size_t to_zero = (size_t)(phdr.p_memsz - phdr.p_filesz);
+
+        if (to_zero) {
+            void *ptr = (void *)(phdr.p_vaddr + phdr.p_filesz);
+            memset(ptr, 0, to_zero);
+        }
+    }
+
+    asm volatile (
+        "jmp %0\n\t"
+        :
+        : "r" (hdr.entry)
+        : "memory"
+    );
+}
diff --git a/src/lib/elf.h b/src/lib/elf.h
new file mode 100644
index 00000000..d3234d83
--- /dev/null
+++ b/src/lib/elf.h
@@ -0,0 +1,8 @@
+#ifndef __LIB__ELF_H__
+#define __LIB__ELF_H__
+
+#include <fs/echfs.h>
+
+int elf_load(struct echfs_file_handle *fd);
+
+#endif
diff --git a/src/main.c b/src/main.c
index bcb4eb4d..3bc04472 100644
--- a/src/main.c
+++ b/src/main.c
@@ -12,6 +12,7 @@ asm (
 #include <lib/config.h>
 #include <fs/echfs.h>
 #include <sys/interrupt.h>
+#include <lib/elf.h>
 
 #define CONFIG_NAME "qloader2.cfg"
 
diff --git a/test/Makefile b/test/Makefile
index e822929d..04d67e36 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -1,3 +1,3 @@
-test.elf:
+test.elf: test.asm linker.ld
 	nasm test.asm -felf32 -o test.o
 	../toolchain/bin/i386-elf-ld test.o -nostdlib -T ./linker.ld -o test.elf
diff --git a/test/test.asm b/test/test.asm
index 037d08b2..4f0bdb03 100644
--- a/test/test.asm
+++ b/test/test.asm
@@ -6,5 +6,7 @@
 section .text
 
 ; Entry point
+global _start
 _start:
-
+    mov eax, 0xdeadbeef
+    jmp $