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 scripts/x86-relocs.c so it will
be compiled before building the arch/x86 tree.

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>

4 files changed, 185 insertions, 63 deletions

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index fd55a2ff3ad8..0435e8a2d20e 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -40,13 +40,12 @@ OBJCOPYFLAGS_vmlinux.bin :=  -R .comment -S
 $(obj)/vmlinux.bin: vmlinux FORCE
         $(call if_changed,objcopy)
 
+targets += vmlinux.bin.all vmlinux.relocs
 
-targets += vmlinux.bin.all vmlinux.relocs relocs
-hostprogs-$(CONFIG_X86_NEED_RELOCS) += relocs
-
-quiet_cmd_relocs = RELOCS  $@
-      cmd_relocs = $(obj)/relocs $< > $@;$(obj)/relocs --abs-relocs $<
-$(obj)/vmlinux.relocs: vmlinux $(obj)/relocs FORCE
+CMD_RELOCS = scripts/x86-relocs
+quiet_cmd_relocs = RELOCS $@
+      cmd_relocs = $(CMD_RELOCS) $< > $@;$(CMD_RELOCS) --abs-relocs $<
+$(obj)/vmlinux.relocs: vmlinux FORCE
         $(call if_changed,relocs)
 
 vmlinux.bin.all-y := $(obj)/vmlinux.bin
diff --git a/scripts/.gitignore b/scripts/.gitignore
index 105b21f08185..68c0f32fdc9b 100644
--- a/scripts/.gitignore
+++ b/scripts/.gitignore
@@ -9,3 +9,4 @@ unifdef
 ihex2fw
 recordmcount
 docproc
+x86-relocs
diff --git a/scripts/Makefile b/scripts/Makefile
index df7678febf27..a241359d2c82 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -8,11 +8,14 @@
 # conmakehash:   Create arrays for initializing the kernel console tables
 # docproc:       Used in Documentation/DocBook
 
+HOST_EXTRACFLAGS += -I$(srctree)/tools/include
+
 hostprogs-$(CONFIG_KALLSYMS)     += kallsyms
 hostprogs-$(CONFIG_LOGO)         += pnmtologo
 hostprogs-$(CONFIG_VT)           += conmakehash
 hostprogs-$(CONFIG_IKCONFIG)     += bin2c
 hostprogs-$(BUILD_C_RECORDMCOUNT) += recordmcount
+hostprogs-$(CONFIG_X86)          += x86-relocs
 
 always          := $(hostprogs-y) $(hostprogs-m)
 
diff --git a/arch/x86/boot/compressed/relocs.c b/scripts/x86-relocs.c
index fb7117a4ade1..02914706e5b9 100644
--- a/arch/x86/boot/compressed/relocs.c
+++ b/scripts/x86-relocs.c
@@ -18,6 +18,8 @@ static void die(char *fmt, ...);
 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;
@@ -28,52 +30,82 @@ struct section {
 };
 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.
  */
-static const char abs_sym_regex[] =
+        [S_ABS] =
         "^(xen_irq_disable_direct_reloc$|"
         "xen_save_fl_direct_reloc$|"
         "VDSO|"
-        "__crc_)";
-static regex_t abs_sym_regex_c;
-static int is_abs_reloc(const char *sym_name)
-{
-        return !regexec(&abs_sym_regex_c, sym_name, 0, NULL, 0);
-}
+        "__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.)
  */
-static const char rel_sym_regex[] =
-        "^_end$";
-static regex_t rel_sym_regex_c;
-static int is_rel_reloc(const char *sym_name)
+        [S_REL] =
+        "^_end$",
+};
+
+
+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 !regexec(&rel_sym_regex_c, sym_name, 0, NULL, 0);
+        return sym_regex[type] &&
+                !regexec(&sym_regex_c[type], sym_name, 0, NULL, 0);
 }
 
-static void regex_init(void)
+static void regex_init(int use_real_mode)
 {
         char errbuf[128];
         int err;
-        
-        err = regcomp(&abs_sym_regex_c, abs_sym_regex,
-                      REG_EXTENDED|REG_NOSUB);
-        if (err) {
-                regerror(err, &abs_sym_regex_c, errbuf, sizeof errbuf);
-                die("%s", errbuf);
-        }
+        int i;
 
-        err = regcomp(&rel_sym_regex_c, rel_sym_regex,
-                      REG_EXTENDED|REG_NOSUB);
-        if (err) {
-                regerror(err, &rel_sym_regex_c, errbuf, sizeof errbuf);
-                die("%s", errbuf);
+        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);
+                }
         }
 }
 
@@ -154,6 +186,10 @@ static const char *rel_type(unsigned type)
                 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";
@@ -189,7 +225,7 @@ static const char *sym_name(const char *sym_strtab, Elf32_Sym *sym)
                 name = sym_strtab + sym->st_name;
         }
         else {
-                name = sec_name(secs[sym->st_shndx].shdr.sh_name);
+                name = sec_name(sym->st_shndx);
         }
         return name;
 }
@@ -472,7 +508,7 @@ static void print_absolute_relocs(void)
                          * Before warning check if this absolute symbol
                          * relocation is harmless.
                          */
-                        if (is_abs_reloc(name) || is_rel_reloc(name))
+                        if (is_reloc(S_ABS, name) || is_reloc(S_REL, name))
                                 continue;
 
                         if (!printed) {
@@ -496,7 +532,8 @@ static void print_absolute_relocs(void)
                 printf("\n");
 }
 
-static void walk_relocs(void (*visit)(Elf32_Rel *rel, Elf32_Sym *sym))
+static void walk_relocs(void (*visit)(Elf32_Rel *rel, Elf32_Sym *sym),
+                        int use_real_mode)
 {
         int i;
         /* Walk through the relocations */
@@ -521,30 +558,62 @@ static void walk_relocs(void (*visit)(Elf32_Rel *rel, Elf32_Sym *sym))
                         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);
-                        /* Don't visit relocations to absolute symbols */
-                        if (sym->st_shndx == SHN_ABS &&
-                            !is_rel_reloc(sym_name(sym_strtab, sym))) {
-                                continue;
-                        }
+
                         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:
-                                /* Visit relocations that need to be adjusted */
+                                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);
                         }
                 }
         }
@@ -552,13 +621,19 @@ static void walk_relocs(void (*visit)(Elf32_Rel *rel, Elf32_Sym *sym))
 
 static void count_reloc(Elf32_Rel *rel, Elf32_Sym *sym)
 {
-        reloc_count += 1;
+        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. */
-        relocs[reloc_idx++] = rel->r_offset;
+        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)
@@ -568,23 +643,41 @@ static int cmp_relocs(const void *va, const void *vb)
         return (*a == *b)? 0 : (*a > *b)? 1 : -1;
 }
 
-static void emit_relocs(int as_text)
+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);
+        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);
+        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) {
@@ -593,58 +686,83 @@ static void emit_relocs(int as_text)
                  */
                 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]);
+                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 {
-                unsigned char buf[4];
-                /* Print a stop */
-                fwrite("\0\0\0\0", 4, 1, stdout);
-                /* Now print each relocation */
-                for (i = 0; i < reloc_count; i++) {
-                        put_unaligned_le32(relocs[i], buf);
-                        fwrite(buf, 4, 1, stdout);
+                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] vmlinux\n");
+        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;
+        int as_text, use_real_mode;
         const char *fname;
         FILE *fp;
         int i;
 
-        regex_init();
-
         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(argv[1], "--abs-syms") == 0) {
+                        if (strcmp(arg, "--abs-syms") == 0) {
                                 show_absolute_syms = 1;
                                 continue;
                         }
-
-                        if (strcmp(argv[1], "--abs-relocs") == 0) {
+                        if (strcmp(arg, "--abs-relocs") == 0) {
                                 show_absolute_relocs = 1;
                                 continue;
                         }
-                        else if (strcmp(argv[1], "--text") == 0) {
+                        if (strcmp(arg, "--text") == 0) {
                                 as_text = 1;
                                 continue;
                         }
+                        if (strcmp(arg, "--realmode") == 0) {
+                                use_real_mode = 1;
+                                continue;
+                        }
                 }
                 else if (!fname) {
                         fname = arg;
@@ -655,6 +773,7 @@ int main(int argc, char **argv)
         if (!fname) {
                 usage();
         }
+        regex_init(use_real_mode);
         fp = fopen(fname, "r");
         if (!fp) {
                 die("Cannot open %s: %s\n",
@@ -673,6 +792,6 @@ int main(int argc, char **argv)
                 print_absolute_relocs();
                 return 0;
         }
-        emit_relocs(as_text);
+        emit_relocs(as_text, use_real_mode);
         return 0;
 }