x86: Regex support and known-movable symbols for relocs, fix _end

This adds a new category of symbols to the relocs program: symbols
which are known to be relative, even though the linker emits them as
absolute; this is the case for symbols that live in the linker script,
which currently applies to _end.

Unfortunately the previous workaround of putting _end in its own empty
section was defeated by newer binutils, which remove empty sections
completely.

This patch also changes the symbol matching to use regular expressions
instead of hardcoded C for specific patterns.

This is a decidedly non-minimal patch: a modified version of the
relocs program is used as part of the Syslinux build, and this 	is
basically a backport to Linux of some of those changes; they have
thus been well tested.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <4AF86211.3070103@zytor.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>

2 files changed, 60 insertions, 31 deletions

diff --git a/arch/x86/boot/compressed/relocs.c b/arch/x86/boot/compressed/relocs.c
index bbeb0c3fbd90..89bbf4e4d05d 100644
--- a/arch/x86/boot/compressed/relocs.c
+++ b/arch/x86/boot/compressed/relocs.c
@@ -9,6 +9,9 @@
 #include <byteswap.h>
 #define USE_BSD
 #include <endian.h>
+#include <regex.h>
+
+static void die(char *fmt, ...);
 
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
 static Elf32_Ehdr ehdr;
@@ -30,25 +33,47 @@ static struct section *secs;
  * the address for which it has been compiled. Don't warn user about
  * absolute relocations present w.r.t these symbols.
  */
-static const char* safe_abs_relocs[] = {
-                "xen_irq_disable_direct_reloc",
-                "xen_save_fl_direct_reloc",
-};
+static const char abs_sym_regex[] =
+        "^(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);
+}
 
-static int is_safe_abs_reloc(const char* sym_name)
+/*
+ * 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)
 {
-        int i;
+        return !regexec(&rel_sym_regex_c, sym_name, 0, NULL, 0);
+}
 
-        for (i = 0; i < ARRAY_SIZE(safe_abs_relocs); i++) {
-                if (!strcmp(sym_name, safe_abs_relocs[i]))
-                        /* Match found */
-                        return 1;
-        }
-        if (strncmp(sym_name, "VDSO", 4) == 0)
-                return 1;
-        if (strncmp(sym_name, "__crc_", 6) == 0)
-                return 1;
-        return 0;
+static void regex_init(void)
+{
+        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);
+        }
+
+        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);
+        }
 }
 
 static void die(char *fmt, ...)
@@ -131,7 +156,7 @@ static const char *rel_type(unsigned type)
 #undef REL_TYPE
         };
         const char *name = "unknown type rel type name";
-        if (type < ARRAY_SIZE(type_name)) {
+        if (type < ARRAY_SIZE(type_name) && type_name[type]) {
                 name = type_name[type];
         }
         return name;
@@ -448,7 +473,7 @@ static void print_absolute_relocs(void)
                          * Before warning check if this absolute symbol
                          * relocation is harmless.
                          */
-                        if (is_safe_abs_reloc(name))
+                        if (is_abs_reloc(name) || is_rel_reloc(name))
                                 continue;
 
                         if (!printed) {
@@ -501,21 +526,26 @@ static void walk_relocs(void (*visit)(Elf32_Rel *rel, Elf32_Sym *sym))
                         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) {
+                        if (sym->st_shndx == SHN_ABS &&
+                            !is_rel_reloc(sym_name(sym_strtab, sym))) {
                                 continue;
                         }
-                        if (r_type == R_386_NONE || r_type == R_386_PC32) {
+                        switch (r_type) {
+                        case R_386_NONE:
+                        case R_386_PC32:
                                 /*
                                  * NONE can be ignored and and PC relative
                                  * relocations don't need to be adjusted.
                                  */
-                        }
-                        else if (r_type == R_386_32) {
+                                break;
+                        case R_386_32:
                                 /* Visit relocations that need to be adjusted */
                                 visit(rel, sym);
-                        }
-                        else {
-                                die("Unsupported relocation type: %d\n", r_type);
+                                break;
+                        default:
+                                die("Unsupported relocation type: %s (%d)\n",
+                                    rel_type(r_type), r_type);
+                                break;
                         }
                 }
         }
@@ -571,16 +601,15 @@ static void emit_relocs(int as_text)
         }
         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]);
+                fwrite("\0\0\0\0", 4, 1, stdout);
                 /* 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]);
+                        fwrite(buf, 4, 1, stdout);
                 }
         }
 }
@@ -598,6 +627,8 @@ int main(int argc, char **argv)
         FILE *fp;
         int i;
 
+        regex_init();
+
         show_absolute_syms = 0;
         show_absolute_relocs = 0;
         as_text = 0;
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index f3f2104408d9..f92a0da608cb 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -319,9 +319,7 @@ SECTIONS
                 __brk_limit = .;
         }
 
-        .end : AT(ADDR(.end) - LOAD_OFFSET) {
-                _end = .;
-        }
+        _end = .;
 
         STABS_DEBUG
         DWARF_DEBUG