elfboot: initial version

.gitignore

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+*.o
+*.elf
+

elfboot/Makefile

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+CFLAGS=-c -Wall -O
+CFLAGS_TEST=-DTEST
+
+all: elfboot elfboot_test
+
+elfboot: elfboot.bin
+	cp $^ $@
+	truncate -s $(shell expr '(' `stat -c '%s' $^` + 4095 ')' / 4096 '*' 4096) $@
+
+elfboot.bin: elfboot.elf
+	objcopy -O binary $^ $@
+
+elfboot.elf: head.o elfboot.raw.o raw.lds
+	ld $(LDFLAGS_RAW) -T raw.lds -o $@ $^
+
+elfboot_test: elfboot.test.o test_main.o
+	gcc $(LDFLAGS) -o $@ $^
+
+elfboot.raw.o: elfboot.c
+	gcc $(CFLAGS) -o $@ $^
+elfboot.test.o: elfboot.c
+	gcc $(CFLAGS) $(CFLAGS_TEST) -o $@ $^
+
+clean:
+	$(RM) elfboot *.bin *.elf elfboot_test *.o
+
+disas:
+	objdump -b binary -m i386:x86-64 -D elfboot.bin

elfboot/elfboot.c

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+#include <elf.h>
+#include "test.h"
+
+#ifdef TEST
+static void *memcpy(void *dest, void *src, unsigned long len)
+{
+	dprintf("Copying %p to %p for %08ld bytes\n", src, dest, len);
+
+	return dest;
+}
+static void *memset(void *dest, int v, unsigned long len)
+{
+	dprintf("Filling %p with %02x for %08ld bytes\n", dest, (unsigned char)v, len);
+
+	return dest;
+}
+#else
+static void *memcpy(void *dest, void *src, unsigned long len)
+{
+	char *d = dest, *s = src;
+
+	for ( ; len ; len--) {
+		*(d++) = *(s++);
+	}
+
+	return d;
+}
+static void *memset(void *dest, int v, unsigned long len)
+{
+	char *d = dest;
+
+	for ( ; len ; len--) {
+		*(d++) = (char)v;
+	}
+
+	return d;
+}
+#endif
+
+static void load_programs(unsigned char *image, Elf64_Phdr *hdrs, int nhdr)
+{
+	int i;
+
+	for (i = 0; i < nhdr; i++) {
+		if (hdrs[i].p_type == PT_LOAD) {
+			dprintf("PT_LOAD : %lx: %lx - %lx (%lx)\n",
+			        hdrs[i].p_vaddr,
+			        hdrs[i].p_offset, hdrs[i].p_filesz,
+			        hdrs[i].p_memsz);
+
+			memcpy((void *)hdrs[i].p_vaddr,
+			       image + hdrs[i].p_offset,
+			       hdrs[i].p_filesz);
+			if (hdrs[i].p_filesz < hdrs[i].p_memsz) {
+				memset((void *)hdrs[i].p_vaddr + 
+				       hdrs[i].p_filesz, 0,
+				       hdrs[i].p_memsz - hdrs[i].p_filesz);
+			}
+		}
+	}
+}
+
+
+/*
+ * Return value: If success, the entry point address. Otherwise, 0.
+ */
+unsigned long elfboot_main(unsigned char *image)
+{
+	Elf64_Ehdr *hdr;
+
+	hdr = (Elf64_Ehdr *)image;
+	if (hdr->e_ident[0] != 0x7f || hdr->e_ident[1] != 'E'
+	    || hdr->e_ident[2] != 'L' || hdr->e_ident[3] != 'F') {
+		return 0;
+	}
+	/* TODO: We may overlap. So copying should be more sophisticated */
+	if (!hdr->e_phoff || hdr->e_phentsize != sizeof(Elf64_Phdr)) {
+		return 0;
+	}
+	load_programs(image, 
+	              (Elf64_Phdr *)(image + hdr->e_phoff), hdr->e_phnum);
+	return hdr->e_entry;
+}
+

elfboot/head.S

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+.text
+.globl _start
+_start:	
+		leaq _stack_end(%rip), %rsp
+		/* preserve arguments */
+		pushq %rdi
+		pushq %rsi
+		pushq %rdx
+		pushq %rcx
+		leaq _stack_end(%rip), %rdi
+		call elfboot_main
+		andq %rax, %rax
+		jz   1f
+		popq %rcx
+		popq %rdx
+		popq %rsi
+		popq %rdi
+		jmpq *%rax				
+1:		
+		cli
+		hlt
+		jmp 1b
+		

elfboot/raw.lds

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+ENTRY(_start)
+
+PHDRS
+{
+	text PT_LOAD;
+	data PT_LOAD;
+}
+
+SECTIONS
+{
+	. = SIZEOF_HEADERS;
+    . = ALIGN(4096);
+	.text :	{
+	      *(.text)
+	} :text
+	.data : {
+	      *(.data)
+	      *(.data.*)
+	} :data
+	.rodata : {
+	      *(.rodata .rodata.*)
+	} :data
+
+	. = ALIGN(8);
+	.bss : {
+	     _bss_start = .;
+	     *(.bss .bss.*)
+	     _bss_end = .;
+         . = ALIGN(4096);
+         _stack_end = .;
+    } :data
+
+	/DISCARD/ : {
+	     *(.eh_frame)
+         *(.note.gnu.build-id)
+	}
+}

elfboot/test.h

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+#ifdef TEST
+#include <stdio.h>
+#include <stdlib.h>
+
+#define dprintf printf
+#else
+#define dprintf(...)
+#endif
+

elfboot/test_main.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+
+unsigned long elfboot_main(unsigned char *image);
+
+int main(int argc, char **argv)
+{
+	int fd;
+	struct stat st;
+	void *p;
+
+	if (argc < 2) {
+		fprintf(stderr, "Usage : %s (elf)\n", argv[0]);
+		return 1;
+	}
+	fd = open(argv[1], O_RDONLY);
+	if (fd < 0){ 
+		perror("open");
+		return 1;
+	}
+
+	fstat(fd, &st);
+	
+	p = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	if (p == MAP_FAILED) {
+		perror("mmap");
+		return 2;
+	}
+
+	printf("read result : %lx\n", elfboot_main(p));
+
+	munmap(p, st.st_size);
+	close(fd);
+
+	return 0;
+}