[PATCH] i386: Relocatable kernel support

This patch modifies the i386 kernel so that if CONFIG_RELOCATABLE is
selected it will be able to be loaded at any 4K aligned address below
1G.  The technique used is to compile the decompressor with -fPIC and
modify it so the decompressor is fully relocatable.  For the main
kernel relocations are generated.  Resulting in a kernel that is relocatable
with no runtime overhead and no need to modify the source code.

A reserved 32bit word in the parameters has been assigned
to serve as a stack so we figure out where are running.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 563 insertions, 0 deletions

diff --git a/arch/i386/boot/compressed/relocs.c b/arch/i386/boot/compressed/relocs.c
new file mode 100644
index 00000000000..0551ceb21be
--- /dev/null
+++ b/arch/i386/boot/compressed/relocs.c
@@ -0,0 +1,563 @@
+#include <stdio.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <elf.h>
+#include <byteswap.h>
+#define USE_BSD
+#include <endian.h>
+
+#define MAX_SHDRS 100
+static Elf32_Ehdr ehdr;
+static Elf32_Shdr shdr[MAX_SHDRS];
+static Elf32_Sym  *symtab[MAX_SHDRS];
+static Elf32_Rel  *reltab[MAX_SHDRS];
+static char *strtab[MAX_SHDRS];
+static unsigned long reloc_count, reloc_idx;
+static unsigned long *relocs;
+
+static void die(char *fmt, ...)
+{
+	va_list ap;
+	va_start(ap, fmt);
+	vfprintf(stderr, fmt, ap);
+	va_end(ap);
+	exit(1);
+}
+
+static const char *sym_type(unsigned type)
+{
+	static const char *type_name[] = {
+#define SYM_TYPE(X) [X] = #X
+		SYM_TYPE(STT_NOTYPE),
+		SYM_TYPE(STT_OBJECT),
+		SYM_TYPE(STT_FUNC),
+		SYM_TYPE(STT_SECTION),
+		SYM_TYPE(STT_FILE),
+		SYM_TYPE(STT_COMMON),
+		SYM_TYPE(STT_TLS),
+#undef SYM_TYPE
+	};
+	const char *name = "unknown sym type name";
+	if (type < sizeof(type_name)/sizeof(type_name[0])) {
+		name = type_name[type];
+	}
+	return name;
+}
+
+static const char *sym_bind(unsigned bind)
+{
+	static const char *bind_name[] = {
+#define SYM_BIND(X) [X] = #X
+		SYM_BIND(STB_LOCAL),
+		SYM_BIND(STB_GLOBAL),
+		SYM_BIND(STB_WEAK),
+#undef SYM_BIND
+	};
+	const char *name = "unknown sym bind name";
+	if (bind < sizeof(bind_name)/sizeof(bind_name[0])) {
+		name = bind_name[bind];
+	}
+	return name;
+}
+
+static const char *sym_visibility(unsigned visibility)
+{
+	static const char *visibility_name[] = {
+#define SYM_VISIBILITY(X) [X] = #X
+		SYM_VISIBILITY(STV_DEFAULT),
+		SYM_VISIBILITY(STV_INTERNAL),
+		SYM_VISIBILITY(STV_HIDDEN),
+		SYM_VISIBILITY(STV_PROTECTED),
+#undef SYM_VISIBILITY
+	};
+	const char *name = "unknown sym visibility name";
+	if (visibility < sizeof(visibility_name)/sizeof(visibility_name[0])) {
+		name = visibility_name[visibility];
+	}
+	return name;
+}
+
+static const char *rel_type(unsigned type)
+{
+	static const char *type_name[] = {
+#define REL_TYPE(X) [X] = #X
+		REL_TYPE(R_386_NONE),
+		REL_TYPE(R_386_32),
+		REL_TYPE(R_386_PC32),
+		REL_TYPE(R_386_GOT32),
+		REL_TYPE(R_386_PLT32),
+		REL_TYPE(R_386_COPY),
+		REL_TYPE(R_386_GLOB_DAT),
+		REL_TYPE(R_386_JMP_SLOT),
+		REL_TYPE(R_386_RELATIVE),
+		REL_TYPE(R_386_GOTOFF),
+		REL_TYPE(R_386_GOTPC),
+#undef REL_TYPE
+	};
+	const char *name = "unknown type rel type name";
+	if (type < sizeof(type_name)/sizeof(type_name[0])) {
+		name = type_name[type];
+	}
+	return name;
+}
+
+static const char *sec_name(unsigned shndx)
+{
+	const char *sec_strtab;
+	const char *name;
+	sec_strtab = strtab[ehdr.e_shstrndx];
+	name = "<noname>";
+	if (shndx < ehdr.e_shnum) {
+		name = sec_strtab + shdr[shndx].sh_name;
+	}
+	else if (shndx == SHN_ABS) {
+		name = "ABSOLUTE";
+	}
+	else if (shndx == SHN_COMMON) {
+		name = "COMMON";
+	}
+	return name;
+}
+
+static const char *sym_name(const char *sym_strtab, Elf32_Sym *sym)
+{
+	const char *name;
+	name = "<noname>";
+	if (sym->st_name) {
+		name = sym_strtab + sym->st_name;
+	}
+	else {
+		name = sec_name(shdr[sym->st_shndx].sh_name);
+	}
+	return name;
+}
+
+
+
+#if BYTE_ORDER == LITTLE_ENDIAN
+#define le16_to_cpu(val) (val)
+#define le32_to_cpu(val) (val)
+#endif
+#if BYTE_ORDER == BIG_ENDIAN
+#define le16_to_cpu(val) bswap_16(val)
+#define le32_to_cpu(val) bswap_32(val)
+#endif
+
+static uint16_t elf16_to_cpu(uint16_t val)
+{
+	return le16_to_cpu(val);
+}
+
+static uint32_t elf32_to_cpu(uint32_t val)
+{
+	return le32_to_cpu(val);
+}
+
+static void read_ehdr(FILE *fp)
+{
+	if (fread(&ehdr, sizeof(ehdr), 1, fp) != 1) {
+		die("Cannot read ELF header: %s\n",
+			strerror(errno));
+	}
+	if (memcmp(ehdr.e_ident, ELFMAG, 4) != 0) {
+		die("No ELF magic\n");
+	}
+	if (ehdr.e_ident[EI_CLASS] != ELFCLASS32) {
+		die("Not a 32 bit executable\n");
+	}
+	if (ehdr.e_ident[EI_DATA] != ELFDATA2LSB) {
+		die("Not a LSB ELF executable\n");
+	}
+	if (ehdr.e_ident[EI_VERSION] != EV_CURRENT) {
+		die("Unknown ELF version\n");
+	}
+	/* Convert the fields to native endian */
+	ehdr.e_type      = elf16_to_cpu(ehdr.e_type);
+	ehdr.e_machine   = elf16_to_cpu(ehdr.e_machine);
+	ehdr.e_version   = elf32_to_cpu(ehdr.e_version);
+	ehdr.e_entry     = elf32_to_cpu(ehdr.e_entry);
+	ehdr.e_phoff     = elf32_to_cpu(ehdr.e_phoff);
+	ehdr.e_shoff     = elf32_to_cpu(ehdr.e_shoff);
+	ehdr.e_flags     = elf32_to_cpu(ehdr.e_flags);
+	ehdr.e_ehsize    = elf16_to_cpu(ehdr.e_ehsize);
+	ehdr.e_phentsize = elf16_to_cpu(ehdr.e_phentsize);
+	ehdr.e_phnum     = elf16_to_cpu(ehdr.e_phnum);
+	ehdr.e_shentsize = elf16_to_cpu(ehdr.e_shentsize);
+	ehdr.e_shnum     = elf16_to_cpu(ehdr.e_shnum);
+	ehdr.e_shstrndx  = elf16_to_cpu(ehdr.e_shstrndx);
+
+	if ((ehdr.e_type != ET_EXEC) && (ehdr.e_type != ET_DYN)) {
+		die("Unsupported ELF header type\n");
+	}
+	if (ehdr.e_machine != EM_386) {
+		die("Not for x86\n");
+	}
+	if (ehdr.e_version != EV_CURRENT) {
+		die("Unknown ELF version\n");
+	}
+	if (ehdr.e_ehsize != sizeof(Elf32_Ehdr)) {
+		die("Bad Elf header size\n");
+	}
+	if (ehdr.e_phentsize != sizeof(Elf32_Phdr)) {
+		die("Bad program header entry\n");
+	}
+	if (ehdr.e_shentsize != sizeof(Elf32_Shdr)) {
+		die("Bad section header entry\n");
+	}
+	if (ehdr.e_shstrndx >= ehdr.e_shnum) {
+		die("String table index out of bounds\n");
+	}
+}
+
+static void read_shdrs(FILE *fp)
+{
+	int i;
+	if (ehdr.e_shnum > MAX_SHDRS) {
+		die("%d section headers supported: %d\n",
+			ehdr.e_shnum, MAX_SHDRS);
+	}
+	if (fseek(fp, ehdr.e_shoff, SEEK_SET) < 0) {
+		die("Seek to %d failed: %s\n",
+			ehdr.e_shoff, strerror(errno));
+	}
+	if (fread(&shdr, sizeof(shdr[0]), ehdr.e_shnum, fp) != ehdr.e_shnum) {
+		die("Cannot read ELF section headers: %s\n",
+			strerror(errno));
+	}
+	for(i = 0; i < ehdr.e_shnum; i++) {
+		shdr[i].sh_name      = elf32_to_cpu(shdr[i].sh_name);
+		shdr[i].sh_type      = elf32_to_cpu(shdr[i].sh_type);
+		shdr[i].sh_flags     = elf32_to_cpu(shdr[i].sh_flags);
+		shdr[i].sh_addr      = elf32_to_cpu(shdr[i].sh_addr);
+		shdr[i].sh_offset    = elf32_to_cpu(shdr[i].sh_offset);
+		shdr[i].sh_size      = elf32_to_cpu(shdr[i].sh_size);
+		shdr[i].sh_link      = elf32_to_cpu(shdr[i].sh_link);
+		shdr[i].sh_info      = elf32_to_cpu(shdr[i].sh_info);
+		shdr[i].sh_addralign = elf32_to_cpu(shdr[i].sh_addralign);
+		shdr[i].sh_entsize   = elf32_to_cpu(shdr[i].sh_entsize);
+	}
+
+}
+
+static void read_strtabs(FILE *fp)
+{
+	int i;
+	for(i = 0; i < ehdr.e_shnum; i++) {
+		if (shdr[i].sh_type != SHT_STRTAB) {
+			continue;
+		}
+		strtab[i] = malloc(shdr[i].sh_size);
+		if (!strtab[i]) {
+			die("malloc of %d bytes for strtab failed\n",
+				shdr[i].sh_size);
+		}
+		if (fseek(fp, shdr[i].sh_offset, SEEK_SET) < 0) {
+			die("Seek to %d failed: %s\n",
+				shdr[i].sh_offset, strerror(errno));
+		}
+		if (fread(strtab[i], 1, shdr[i].sh_size, fp) != shdr[i].sh_size) {
+			die("Cannot read symbol table: %s\n",
+				strerror(errno));
+		}
+	}
+}
+
+static void read_symtabs(FILE *fp)
+{
+	int i,j;
+	for(i = 0; i < ehdr.e_shnum; i++) {
+		if (shdr[i].sh_type != SHT_SYMTAB) {
+			continue;
+		}
+		symtab[i] = malloc(shdr[i].sh_size);
+		if (!symtab[i]) {
+			die("malloc of %d bytes for symtab failed\n",
+				shdr[i].sh_size);
+		}
+		if (fseek(fp, shdr[i].sh_offset, SEEK_SET) < 0) {
+			die("Seek to %d failed: %s\n",
+				shdr[i].sh_offset, strerror(errno));
+		}
+		if (fread(symtab[i], 1, shdr[i].sh_size, fp) != shdr[i].sh_size) {
+			die("Cannot read symbol table: %s\n",
+				strerror(errno));
+		}
+		for(j = 0; j < shdr[i].sh_size/sizeof(symtab[i][0]); j++) {
+			symtab[i][j].st_name  = elf32_to_cpu(symtab[i][j].st_name);
+			symtab[i][j].st_value = elf32_to_cpu(symtab[i][j].st_value);
+			symtab[i][j].st_size  = elf32_to_cpu(symtab[i][j].st_size);
+			symtab[i][j].st_shndx = elf16_to_cpu(symtab[i][j].st_shndx);
+		}
+	}
+}
+
+
+static void read_relocs(FILE *fp)
+{
+	int i,j;
+	for(i = 0; i < ehdr.e_shnum; i++) {
+		if (shdr[i].sh_type != SHT_REL) {
+			continue;
+		}
+		reltab[i] = malloc(shdr[i].sh_size);
+		if (!reltab[i]) {
+			die("malloc of %d bytes for relocs failed\n",
+				shdr[i].sh_size);
+		}
+		if (fseek(fp, shdr[i].sh_offset, SEEK_SET) < 0) {
+			die("Seek to %d failed: %s\n",
+				shdr[i].sh_offset, strerror(errno));
+		}
+		if (fread(reltab[i], 1, shdr[i].sh_size, fp) != shdr[i].sh_size) {
+			die("Cannot read symbol table: %s\n",
+				strerror(errno));
+		}
+		for(j = 0; j < shdr[i].sh_size/sizeof(reltab[0][0]); j++) {
+			reltab[i][j].r_offset = elf32_to_cpu(reltab[i][j].r_offset);
+			reltab[i][j].r_info   = elf32_to_cpu(reltab[i][j].r_info);
+		}
+	}
+}
+
+
+static void print_absolute_symbols(void)
+{
+	int i;
+	printf("Absolute symbols\n");
+	printf(" Num:    Value Size  Type       Bind        Visibility  Name\n");
+	for(i = 0; i < ehdr.e_shnum; i++) {
+		char *sym_strtab;
+		Elf32_Sym *sh_symtab;
+		int j;
+		if (shdr[i].sh_type != SHT_SYMTAB) {
+			continue;
+		}
+		sh_symtab = symtab[i];
+		sym_strtab = strtab[shdr[i].sh_link];
+		for(j = 0; j < shdr[i].sh_size/sizeof(symtab[0][0]); j++) {
+			Elf32_Sym *sym;
+			const char *name;
+			sym = &symtab[i][j];
+			name = sym_name(sym_strtab, sym);
+			if (sym->st_shndx != SHN_ABS) {
+				continue;
+			}
+			printf("%5d %08x %5d %10s %10s %12s %s\n",
+				j, sym->st_value, sym->st_size,
+				sym_type(ELF32_ST_TYPE(sym->st_info)),
+				sym_bind(ELF32_ST_BIND(sym->st_info)),
+				sym_visibility(ELF32_ST_VISIBILITY(sym->st_other)),
+				name);
+		}
+	}
+	printf("\n");
+}
+
+static void print_absolute_relocs(void)
+{
+	int i;
+	printf("Absolute relocations\n");
+	printf("Offset     Info     Type     Sym.Value Sym.Name\n");
+	for(i = 0; i < ehdr.e_shnum; i++) {
+		char *sym_strtab;
+		Elf32_Sym *sh_symtab;
+		unsigned sec_applies, sec_symtab;
+		int j;
+		if (shdr[i].sh_type != SHT_REL) {
+			continue;
+		}
+		sec_symtab  = shdr[i].sh_link;
+		sec_applies = shdr[i].sh_info;
+		if (!(shdr[sec_applies].sh_flags & SHF_ALLOC)) {
+			continue;
+		}
+		sh_symtab = symtab[sec_symtab];
+		sym_strtab = strtab[shdr[sec_symtab].sh_link];
+		for(j = 0; j < shdr[i].sh_size/sizeof(reltab[0][0]); j++) {
+			Elf32_Rel *rel;
+			Elf32_Sym *sym;
+			const char *name;
+			rel = &reltab[i][j];
+			sym = &sh_symtab[ELF32_R_SYM(rel->r_info)];
+			name = sym_name(sym_strtab, sym);
+			if (sym->st_shndx != SHN_ABS) {
+				continue;
+			}
+			printf("%08x %08x %10s %08x  %s\n",
+				rel->r_offset,
+				rel->r_info,
+				rel_type(ELF32_R_TYPE(rel->r_info)),
+				sym->st_value,
+				name);
+		}
+	}
+	printf("\n");
+}
+
+static void walk_relocs(void (*visit)(Elf32_Rel *rel, Elf32_Sym *sym))
+{
+	int i;
+	/* Walk through the relocations */
+	for(i = 0; i < ehdr.e_shnum; i++) {
+		char *sym_strtab;
+		Elf32_Sym *sh_symtab;
+		unsigned sec_applies, sec_symtab;
+		int j;
+		if (shdr[i].sh_type != SHT_REL) {
+			continue;
+		}
+		sec_symtab  = shdr[i].sh_link;
+		sec_applies = shdr[i].sh_info;
+		if (!(shdr[sec_applies].sh_flags & SHF_ALLOC)) {
+			continue;
+		}
+		sh_symtab = symtab[sec_symtab];
+		sym_strtab = strtab[shdr[sec_symtab].sh_link];
+		for(j = 0; j < shdr[i].sh_size/sizeof(reltab[0][0]); j++) {
+			Elf32_Rel *rel;
+			Elf32_Sym *sym;
+			unsigned r_type;
+			rel = &reltab[i][j];
+			sym = &sh_symtab[ELF32_R_SYM(rel->r_info)];
+			r_type = ELF32_R_TYPE(rel->r_info);
+			/* Don't visit relocations to absolute symbols */
+			if (sym->st_shndx == SHN_ABS) {
+				continue;
+			}
+			if (r_type == R_386_PC32) {
+				/* PC relative relocations don't need to be adjusted */
+			}
+			else if (r_type == R_386_32) {
+				/* Visit relocations that need to be adjusted */
+				visit(rel, sym);
+			}
+			else {
+				die("Unsupported relocation type: %d\n", r_type);
+			}
+		}
+	}
+}
+
+static void count_reloc(Elf32_Rel *rel, Elf32_Sym *sym)
+{
+	reloc_count += 1;
+}
+
+static void collect_reloc(Elf32_Rel *rel, Elf32_Sym *sym)
+{
+	/* Remember the address that needs to be adjusted. */
+	relocs[reloc_idx++] = rel->r_offset;
+}
+
+static int cmp_relocs(const void *va, const void *vb)
+{
+	const unsigned long *a, *b;
+	a = va; b = vb;
+	return (*a == *b)? 0 : (*a > *b)? 1 : -1;
+}
+
+static void emit_relocs(int as_text)
+{
+	int i;
+	/* Count how many relocations I have and allocate space for them. */
+	reloc_count = 0;
+	walk_relocs(count_reloc);
+	relocs = malloc(reloc_count * sizeof(relocs[0]));
+	if (!relocs) {
+		die("malloc of %d entries for relocs failed\n",
+			reloc_count);
+	}
+	/* Collect up the relocations */
+	reloc_idx = 0;
+	walk_relocs(collect_reloc);
+
+	/* Order the relocations for more efficient processing */
+	qsort(relocs, reloc_count, sizeof(relocs[0]), cmp_relocs);
+
+	/* Print the relocations */
+	if (as_text) {
+		/* Print the relocations in a form suitable that
+		 * gas will like.
+		 */
+		printf(".section \".data.reloc\",\"a\"\n");
+		printf(".balign 4\n");
+		for(i = 0; i < reloc_count; i++) {
+			printf("\t .long 0x%08lx\n", relocs[i]);
+		}
+		printf("\n");
+	}
+	else {
+		unsigned char buf[4];
+		buf[0] = buf[1] = buf[2] = buf[3] = 0;
+		/* Print a stop */
+		printf("%c%c%c%c", buf[0], buf[1], buf[2], buf[3]);
+		/* Now print each relocation */
+		for(i = 0; i < reloc_count; i++) {
+			buf[0] = (relocs[i] >>  0) & 0xff;
+			buf[1] = (relocs[i] >>  8) & 0xff;
+			buf[2] = (relocs[i] >> 16) & 0xff;
+			buf[3] = (relocs[i] >> 24) & 0xff;
+			printf("%c%c%c%c", buf[0], buf[1], buf[2], buf[3]);
+		}
+	}
+}
+
+static void usage(void)
+{
+	die("i386_reloc [--abs | --text] vmlinux\n");
+}
+
+int main(int argc, char **argv)
+{
+	int show_absolute;
+	int as_text;
+	const char *fname;
+	FILE *fp;
+	int i;
+
+	show_absolute = 0;
+	as_text = 0;
+	fname = NULL;
+	for(i = 1; i < argc; i++) {
+		char *arg = argv[i];
+		if (*arg == '-') {
+			if (strcmp(argv[1], "--abs") == 0) {
+				show_absolute = 1;
+				continue;
+			}
+			else if (strcmp(argv[1], "--text") == 0) {
+				as_text = 1;
+				continue;
+			}
+		}
+		else if (!fname) {
+			fname = arg;
+			continue;
+		}
+		usage();
+	}
+	if (!fname) {
+		usage();
+	}
+	fp = fopen(fname, "r");
+	if (!fp) {
+		die("Cannot open %s: %s\n",
+			fname, strerror(errno));
+	}
+	read_ehdr(fp);
+	read_shdrs(fp);
+	read_strtabs(fp);
+	read_symtabs(fp);
+	read_relocs(fp);
+	if (show_absolute) {
+		print_absolute_symbols();
+		print_absolute_relocs();
+		return 0;
+	}
+	emit_relocs(as_text);
+	return 0;
+}