x86, realmode: 16-bit real-mode code support for relocs tool

A new option is added to the relocs tool called '--realmode'.
This option causes the generation of 16-bit segment relocations
and 32-bit linear relocations for the real-mode code. When
the real-mode code is moved to the low-memory during kernel
initialization, these relocation entries can be used to
relocate the code properly.

In the assembly code 16-bit segment relocations must be relative
to the 'real_mode_seg' absolute symbol. Linear relocations must be
relative to a symbol prefixed with 'pa_'.

16-bit segment relocation is used to load cs:ip in 16-bit code.
Linear relocations are used in the 32-bit code for relocatable
data references. They are declared in the linker script of the
real-mode code.

The relocs tool is moved to arch/x86/tools/relocs.c, and added new
target archscripts that can be used to build scripts needed building
an architecture.  be compiled before building the arch/x86 tree.

[ hpa: accelerating this because it detects invalid absolute
  relocations, a serious bug in binutils 2.22.52.0.x which currently
  produces bad kernels. ]

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1336501366-28617-2-git-send-email-jarkko.sakkinen@intel.com
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: <stable@vger.kernel.org>

3 files changed, 802 insertions, 0 deletions

diff --git a/arch/x86/tools/.gitignore b/arch/x86/tools/.gitignore
new file mode 100644
index 000000000000..be0ed065249b
--- /dev/null
+++ b/arch/x86/tools/.gitignore
@@ -0,0 +1 @@
+relocs
diff --git a/arch/x86/tools/Makefile b/arch/x86/tools/Makefile
index d511aa97533a..733057b435b0 100644
--- a/arch/x86/tools/Makefile
+++ b/arch/x86/tools/Makefile
@@ -36,3 +36,7 @@ HOSTCFLAGS_insn_sanity.o := -Wall -I$(objtree)/arch/x86/lib/ -I$(srctree)/arch/x
 $(obj)/test_get_len.o: $(srctree)/arch/x86/lib/insn.c $(srctree)/arch/x86/lib/inat.c $(srctree)/arch/x86/include/asm/inat_types.h $(srctree)/arch/x86/include/asm/inat.h $(srctree)/arch/x86/include/asm/insn.h $(objtree)/arch/x86/lib/inat-tables.c
 
 $(obj)/insn_sanity.o: $(srctree)/arch/x86/lib/insn.c $(srctree)/arch/x86/lib/inat.c $(srctree)/arch/x86/include/asm/inat_types.h $(srctree)/arch/x86/include/asm/inat.h $(srctree)/arch/x86/include/asm/insn.h $(objtree)/arch/x86/lib/inat-tables.c
+
+HOST_EXTRACFLAGS += -I$(srctree)/tools/include
+hostprogs-y     += relocs
+relocs: $(obj)/relocs
diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
new file mode 100644
index 000000000000..02914706e5b9
--- /dev/null
+++ b/arch/x86/tools/relocs.c
@@ -0,0 +1,797 @@
+#include <stdio.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <elf.h>
+#include <byteswap.h>
+#define USE_BSD
+#include <endian.h>
+#include <regex.h>
+#include <tools/le_byteshift.h>
+
+static void die(char *fmt, ...);
+
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+static Elf32_Ehdr ehdr;
+static unsigned long reloc_count, reloc_idx;
+static unsigned long *relocs;
+static unsigned long reloc16_count, reloc16_idx;
+static unsigned long *relocs16;
+
+struct section {
+        Elf32_Shdr     shdr;
+        struct section *link;
+        Elf32_Sym      *symtab;
+        Elf32_Rel      *reltab;
+        char           *strtab;
+};
+static struct section *secs;
+
+enum symtype {
+        S_ABS,
+        S_REL,
+        S_SEG,
+        S_LIN,
+        S_NSYMTYPES
+};
+
+static const char * const sym_regex_kernel[S_NSYMTYPES] = {
+/*
+ * Following symbols have been audited. There values are constant and do
+ * not change if bzImage is loaded at a different physical address than
+ * the address for which it has been compiled. Don't warn user about
+ * absolute relocations present w.r.t these symbols.
+ */
+        [S_ABS] =
+        "^(xen_irq_disable_direct_reloc$|"
+        "xen_save_fl_direct_reloc$|"
+        "VDSO|"
+        "__crc_)",
+
+/*
+ * These symbols are known to be relative, even if the linker marks them
+ * as absolute (typically defined outside any section in the linker script.)
+ */
+        [S_REL] =
+        "^_end$",
+};
+
+
+static const char * const sym_regex_realmode[S_NSYMTYPES] = {
+/*
+ * These are 16-bit segment symbols when compiling 16-bit code.
+ */
+        [S_SEG] =
+        "^real_mode_seg$",
+
+/*
+ * These are offsets belonging to segments, as opposed to linear addresses,
+ * when compiling 16-bit code.
+ */
+        [S_LIN] =
+        "^pa_",
+};
+
+static const char * const *sym_regex;
+
+static regex_t sym_regex_c[S_NSYMTYPES];
+static int is_reloc(enum symtype type, const char *sym_name)
+{
+        return sym_regex[type] &&
+                !regexec(&sym_regex_c[type], sym_name, 0, NULL, 0);
+}
+
+static void regex_init(int use_real_mode)
+{
+        char errbuf[128];
+        int err;
+        int i;
+
+        if (use_real_mode)
+                sym_regex = sym_regex_realmode;
+        else
+                sym_regex = sym_regex_kernel;
+
+        for (i = 0; i < S_NSYMTYPES; i++) {
+                if (!sym_regex[i])
+                        continue;
+
+                err = regcomp(&sym_regex_c[i], sym_regex[i],
+                              REG_EXTENDED|REG_NOSUB);
+
+                if (err) {
+                        regerror(err, &sym_regex_c[i], errbuf, sizeof errbuf);
+                        die("%s", errbuf);
+                }
+        }
+}
+
+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 < ARRAY_SIZE(type_name)) {
+                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 < ARRAY_SIZE(bind_name)) {
+                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 < ARRAY_SIZE(visibility_name)) {
+                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),
+                REL_TYPE(R_386_8),
+                REL_TYPE(R_386_PC8),
+                REL_TYPE(R_386_16),
+                REL_TYPE(R_386_PC16),
+#undef REL_TYPE
+        };
+        const char *name = "unknown type rel type name";
+        if (type < ARRAY_SIZE(type_name) && type_name[type]) {
+                name = type_name[type];
+        }
+        return name;
+}
+
+static const char *sec_name(unsigned shndx)
+{
+        const char *sec_strtab;
+        const char *name;
+        sec_strtab = secs[ehdr.e_shstrndx].strtab;
+        name = "<noname>";
+        if (shndx < ehdr.e_shnum) {
+                name = sec_strtab + secs[shndx].shdr.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(sym->st_shndx);
+        }
+        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, SELFMAG) != 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;
+        Elf32_Shdr shdr;
+
+        secs = calloc(ehdr.e_shnum, sizeof(struct section));
+        if (!secs) {
+                die("Unable to allocate %d section headers\n",
+                    ehdr.e_shnum);
+        }
+        if (fseek(fp, ehdr.e_shoff, SEEK_SET) < 0) {
+                die("Seek to %d failed: %s\n",
+                        ehdr.e_shoff, strerror(errno));
+        }
+        for (i = 0; i < ehdr.e_shnum; i++) {
+                struct section *sec = &secs[i];
+                if (fread(&shdr, sizeof shdr, 1, fp) != 1)
+                        die("Cannot read ELF section headers %d/%d: %s\n",
+                            i, ehdr.e_shnum, strerror(errno));
+                sec->shdr.sh_name      = elf32_to_cpu(shdr.sh_name);
+                sec->shdr.sh_type      = elf32_to_cpu(shdr.sh_type);
+                sec->shdr.sh_flags     = elf32_to_cpu(shdr.sh_flags);
+                sec->shdr.sh_addr      = elf32_to_cpu(shdr.sh_addr);
+                sec->shdr.sh_offset    = elf32_to_cpu(shdr.sh_offset);
+                sec->shdr.sh_size      = elf32_to_cpu(shdr.sh_size);
+                sec->shdr.sh_link      = elf32_to_cpu(shdr.sh_link);
+                sec->shdr.sh_info      = elf32_to_cpu(shdr.sh_info);
+                sec->shdr.sh_addralign = elf32_to_cpu(shdr.sh_addralign);
+                sec->shdr.sh_entsize   = elf32_to_cpu(shdr.sh_entsize);
+                if (sec->shdr.sh_link < ehdr.e_shnum)
+                        sec->link = &secs[sec->shdr.sh_link];
+        }
+
+}
+
+static void read_strtabs(FILE *fp)
+{
+        int i;
+        for (i = 0; i < ehdr.e_shnum; i++) {
+                struct section *sec = &secs[i];
+                if (sec->shdr.sh_type != SHT_STRTAB) {
+                        continue;
+                }
+                sec->strtab = malloc(sec->shdr.sh_size);
+                if (!sec->strtab) {
+                        die("malloc of %d bytes for strtab failed\n",
+                                sec->shdr.sh_size);
+                }
+                if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0) {
+                        die("Seek to %d failed: %s\n",
+                                sec->shdr.sh_offset, strerror(errno));
+                }
+                if (fread(sec->strtab, 1, sec->shdr.sh_size, fp)
+                    != sec->shdr.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++) {
+                struct section *sec = &secs[i];
+                if (sec->shdr.sh_type != SHT_SYMTAB) {
+                        continue;
+                }
+                sec->symtab = malloc(sec->shdr.sh_size);
+                if (!sec->symtab) {
+                        die("malloc of %d bytes for symtab failed\n",
+                                sec->shdr.sh_size);
+                }
+                if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0) {
+                        die("Seek to %d failed: %s\n",
+                                sec->shdr.sh_offset, strerror(errno));
+                }
+                if (fread(sec->symtab, 1, sec->shdr.sh_size, fp)
+                    != sec->shdr.sh_size) {
+                        die("Cannot read symbol table: %s\n",
+                                strerror(errno));
+                }
+                for (j = 0; j < sec->shdr.sh_size/sizeof(Elf32_Sym); j++) {
+                        Elf32_Sym *sym = &sec->symtab[j];
+                        sym->st_name  = elf32_to_cpu(sym->st_name);
+                        sym->st_value = elf32_to_cpu(sym->st_value);
+                        sym->st_size  = elf32_to_cpu(sym->st_size);
+                        sym->st_shndx = elf16_to_cpu(sym->st_shndx);
+                }
+        }
+}
+
+
+static void read_relocs(FILE *fp)
+{
+        int i,j;
+        for (i = 0; i < ehdr.e_shnum; i++) {
+                struct section *sec = &secs[i];
+                if (sec->shdr.sh_type != SHT_REL) {
+                        continue;
+                }
+                sec->reltab = malloc(sec->shdr.sh_size);
+                if (!sec->reltab) {
+                        die("malloc of %d bytes for relocs failed\n",
+                                sec->shdr.sh_size);
+                }
+                if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0) {
+                        die("Seek to %d failed: %s\n",
+                                sec->shdr.sh_offset, strerror(errno));
+                }
+                if (fread(sec->reltab, 1, sec->shdr.sh_size, fp)
+                    != sec->shdr.sh_size) {
+                        die("Cannot read symbol table: %s\n",
+                                strerror(errno));
+                }
+                for (j = 0; j < sec->shdr.sh_size/sizeof(Elf32_Rel); j++) {
+                        Elf32_Rel *rel = &sec->reltab[j];
+                        rel->r_offset = elf32_to_cpu(rel->r_offset);
+                        rel->r_info   = elf32_to_cpu(rel->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++) {
+                struct section *sec = &secs[i];
+                char *sym_strtab;
+                int j;
+
+                if (sec->shdr.sh_type != SHT_SYMTAB) {
+                        continue;
+                }
+                sym_strtab = sec->link->strtab;
+                for (j = 0; j < sec->shdr.sh_size/sizeof(Elf32_Sym); j++) {
+                        Elf32_Sym *sym;
+                        const char *name;
+                        sym = &sec->symtab[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, printed = 0;
+
+        for (i = 0; i < ehdr.e_shnum; i++) {
+                struct section *sec = &secs[i];
+                struct section *sec_applies, *sec_symtab;
+                char *sym_strtab;
+                Elf32_Sym *sh_symtab;
+                int j;
+                if (sec->shdr.sh_type != SHT_REL) {
+                        continue;
+                }
+                sec_symtab  = sec->link;
+                sec_applies = &secs[sec->shdr.sh_info];
+                if (!(sec_applies->shdr.sh_flags & SHF_ALLOC)) {
+                        continue;
+                }
+                sh_symtab  = sec_symtab->symtab;
+                sym_strtab = sec_symtab->link->strtab;
+                for (j = 0; j < sec->shdr.sh_size/sizeof(Elf32_Rel); j++) {
+                        Elf32_Rel *rel;
+                        Elf32_Sym *sym;
+                        const char *name;
+                        rel = &sec->reltab[j];
+                        sym = &sh_symtab[ELF32_R_SYM(rel->r_info)];
+                        name = sym_name(sym_strtab, sym);
+                        if (sym->st_shndx != SHN_ABS) {
+                                continue;
+                        }
+
+                        /* Absolute symbols are not relocated if bzImage is
+                         * loaded at a non-compiled address. Display a warning
+                         * to user at compile time about the absolute
+                         * relocations present.
+                         *
+                         * User need to audit the code to make sure
+                         * some symbols which should have been section
+                         * relative have not become absolute because of some
+                         * linker optimization or wrong programming usage.
+                         *
+                         * Before warning check if this absolute symbol
+                         * relocation is harmless.
+                         */
+                        if (is_reloc(S_ABS, name) || is_reloc(S_REL, name))
+                                continue;
+
+                        if (!printed) {
+                                printf("WARNING: Absolute relocations"
+                                        " present\n");
+                                printf("Offset     Info     Type     Sym.Value "
+                                        "Sym.Name\n");
+                                printed = 1;
+                        }
+
+                        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);
+                }
+        }
+
+        if (printed)
+                printf("\n");
+}
+
+static void walk_relocs(void (*visit)(Elf32_Rel *rel, Elf32_Sym *sym),
+                        int use_real_mode)
+{
+        int i;
+        /* Walk through the relocations */
+        for (i = 0; i < ehdr.e_shnum; i++) {
+                char *sym_strtab;
+                Elf32_Sym *sh_symtab;
+                struct section *sec_applies, *sec_symtab;
+                int j;
+                struct section *sec = &secs[i];
+
+                if (sec->shdr.sh_type != SHT_REL) {
+                        continue;
+                }
+                sec_symtab  = sec->link;
+                sec_applies = &secs[sec->shdr.sh_info];
+                if (!(sec_applies->shdr.sh_flags & SHF_ALLOC)) {
+                        continue;
+                }
+                sh_symtab = sec_symtab->symtab;
+                sym_strtab = sec_symtab->link->strtab;
+                for (j = 0; j < sec->shdr.sh_size/sizeof(Elf32_Rel); j++) {
+                        Elf32_Rel *rel;
+                        Elf32_Sym *sym;
+                        unsigned r_type;
+                        const char *symname;
+                        rel = &sec->reltab[j];
+                        sym = &sh_symtab[ELF32_R_SYM(rel->r_info)];
+                        r_type = ELF32_R_TYPE(rel->r_info);
+
+                        switch (r_type) {
+                        case R_386_NONE:
+                        case R_386_PC32:
+                        case R_386_PC16:
+                        case R_386_PC8:
+                                /*
+                                 * NONE can be ignored and and PC relative
+                                 * relocations don't need to be adjusted.
+                                 */
+                                break;
+
+                        case R_386_16:
+                                symname = sym_name(sym_strtab, sym);
+                                if (!use_real_mode)
+                                        goto bad;
+                                if (sym->st_shndx == SHN_ABS) {
+                                        if (is_reloc(S_ABS, symname))
+                                                break;
+                                        else if (!is_reloc(S_SEG, symname))
+                                                goto bad;
+                                } else {
+                                        if (is_reloc(S_LIN, symname))
+                                                goto bad;
+                                        else
+                                                break;
+                                }
+                                visit(rel, sym);
+                                break;
+
+                        case R_386_32:
+                                symname = sym_name(sym_strtab, sym);
+                                if (sym->st_shndx == SHN_ABS) {
+                                        if (is_reloc(S_ABS, symname))
+                                                break;
+                                        else if (!is_reloc(S_REL, symname))
+                                                goto bad;
+                                } else {
+                                        if (use_real_mode &&
+                                            !is_reloc(S_LIN, symname))
+                                                break;
+                                }
+                                visit(rel, sym);
+                                break;
+                        default:
+                                die("Unsupported relocation type: %s (%d)\n",
+                                    rel_type(r_type), r_type);
+                                break;
+                        bad:
+                                symname = sym_name(sym_strtab, sym);
+                                die("Invalid %s relocation: %s\n",
+                                    rel_type(r_type), symname);
+                        }
+                }
+        }
+}
+
+static void count_reloc(Elf32_Rel *rel, Elf32_Sym *sym)
+{
+        if (ELF32_R_TYPE(rel->r_info) == R_386_16)
+                reloc16_count++;
+        else
+                reloc_count++;
+}
+
+static void collect_reloc(Elf32_Rel *rel, Elf32_Sym *sym)
+{
+        /* Remember the address that needs to be adjusted. */
+        if (ELF32_R_TYPE(rel->r_info) == R_386_16)
+                relocs16[reloc16_idx++] = rel->r_offset;
+        else
+                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 int write32(unsigned int v, FILE *f)
+{
+        unsigned char buf[4];
+
+        put_unaligned_le32(v, buf);
+        return fwrite(buf, 1, 4, f) == 4 ? 0 : -1;
+}
+
+static void emit_relocs(int as_text, int use_real_mode)
+{
+        int i;
+        /* Count how many relocations I have and allocate space for them. */
+        reloc_count = 0;
+        walk_relocs(count_reloc, use_real_mode);
+        relocs = malloc(reloc_count * sizeof(relocs[0]));
+        if (!relocs) {
+                die("malloc of %d entries for relocs failed\n",
+                        reloc_count);
+        }
+
+        relocs16 = malloc(reloc16_count * sizeof(relocs[0]));
+        if (!relocs16) {
+                die("malloc of %d entries for relocs16 failed\n",
+                        reloc16_count);
+        }
+        /* Collect up the relocations */
+        reloc_idx = 0;
+        walk_relocs(collect_reloc, use_real_mode);
+
+        if (reloc16_count && !use_real_mode)
+                die("Segment relocations found but --realmode not specified\n");
+
+        /* Order the relocations for more efficient processing */
+        qsort(relocs, reloc_count, sizeof(relocs[0]), cmp_relocs);
+        qsort(relocs16, reloc16_count, sizeof(relocs16[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");
+                if (use_real_mode) {
+                        printf("\t.long %lu\n", reloc16_count);
+                        for (i = 0; i < reloc16_count; i++)
+                                printf("\t.long 0x%08lx\n", relocs16[i]);
+                        printf("\t.long %lu\n", reloc_count);
+                        for (i = 0; i < reloc_count; i++) {
+                                printf("\t.long 0x%08lx\n", relocs[i]);
+                        }
+                } else {
+                        /* Print a stop */
+                        printf("\t.long 0x%08lx\n", (unsigned long)0);
+                        for (i = 0; i < reloc_count; i++) {
+                                printf("\t.long 0x%08lx\n", relocs[i]);
+                        }
+                }
+
+                printf("\n");
+        }
+        else {
+                if (use_real_mode) {
+                        write32(reloc16_count, stdout);
+                        for (i = 0; i < reloc16_count; i++)
+                                write32(relocs16[i], stdout);
+                        write32(reloc_count, stdout);
+
+                        /* Now print each relocation */
+                        for (i = 0; i < reloc_count; i++)
+                                write32(relocs[i], stdout);
+                } else {
+                        /* Print a stop */
+                        write32(0, stdout);
+
+                        /* Now print each relocation */
+                        for (i = 0; i < reloc_count; i++) {
+                                write32(relocs[i], stdout);
+                        }
+                }
+        }
+}
+
+static void usage(void)
+{
+        die("relocs [--abs-syms|--abs-relocs|--text|--realmode] vmlinux\n");
+}
+
+int main(int argc, char **argv)
+{
+        int show_absolute_syms, show_absolute_relocs;
+        int as_text, use_real_mode;
+        const char *fname;
+        FILE *fp;
+        int i;
+
+        show_absolute_syms = 0;
+        show_absolute_relocs = 0;
+        as_text = 0;
+        use_real_mode = 0;
+        fname = NULL;
+        for (i = 1; i < argc; i++) {
+                char *arg = argv[i];
+                if (*arg == '-') {
+                        if (strcmp(arg, "--abs-syms") == 0) {
+                                show_absolute_syms = 1;
+                                continue;
+                        }
+                        if (strcmp(arg, "--abs-relocs") == 0) {
+                                show_absolute_relocs = 1;
+                                continue;
+                        }
+                        if (strcmp(arg, "--text") == 0) {
+                                as_text = 1;
+                                continue;
+                        }
+                        if (strcmp(arg, "--realmode") == 0) {
+                                use_real_mode = 1;
+                                continue;
+                        }
+                }
+                else if (!fname) {
+                        fname = arg;
+                        continue;
+                }
+                usage();
+        }
+        if (!fname) {
+                usage();
+        }
+        regex_init(use_real_mode);
+        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_syms) {
+                print_absolute_symbols();
+                return 0;
+        }
+        if (show_absolute_relocs) {
+                print_absolute_relocs();
+                return 0;
+        }
+        emit_relocs(as_text, use_real_mode);
+        return 0;
+}