[PATCH] i386: Warn upon absolute relocations being present

o Relocations generated w.r.t absolute symbols are not processed as by
  definition, absolute symbols are not to be relocated. Explicitly warn
  user about absolutions relocations present at compile time.

o These relocations get introduced either due to linker optimizations or
  some programming oversights.

o Also create a list of symbols which have been audited to be safe and
  don't emit warnings for these.

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

diff --git a/arch/i386/boot/compressed/Makefile b/arch/i386/boot/compressed/Makefile
index cc28da3a881e12015aad5a63f2d88ce0a9afd0af..a661217f33ec4eeba811cb9d987f626f5f7c3838 100644 (file)
--- a/arch/i386/boot/compressed/Makefile
+++ b/arch/i386/boot/compressed/Makefile
@@ -20,7 +20,7 @@ $(obj)/vmlinux.bin: vmlinux FORCE
        $(call if_changed,objcopy)
 
 quiet_cmd_relocs = RELOCS  $@
-      cmd_relocs = $(obj)/relocs $< > $@
+      cmd_relocs = $(obj)/relocs $< > $@;$(obj)/relocs --abs-relocs $<
 $(obj)/vmlinux.relocs: vmlinux $(obj)/relocs FORCE
        $(call if_changed,relocs)
 

diff --git a/arch/i386/boot/compressed/relocs.c b/arch/i386/boot/compressed/relocs.c
index 0551ceb21bedccae8608405e1bcf9ba1353e4434..468da89153c470ee2311a30ac445cabd2301755b 100644 (file)
--- a/arch/i386/boot/compressed/relocs.c
+++ b/arch/i386/boot/compressed/relocs.c
@@ -19,6 +19,33 @@ static char *strtab[MAX_SHDRS];
 static unsigned long reloc_count, reloc_idx;
 static unsigned long *relocs;
 
+/*
+ * 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* safe_abs_relocs[] = {
+               "__kernel_vsyscall",
+               "__kernel_rt_sigreturn",
+               "__kernel_sigreturn",
+               "SYSENTER_RETURN",
+};
+
+static int is_safe_abs_reloc(const char* sym_name)
+{
+       int i, array_size;
+
+       array_size = sizeof(safe_abs_relocs)/sizeof(char*);
+
+       for(i = 0; i < array_size; i++) {
+               if (!strcmp(sym_name, safe_abs_relocs[i]))
+                       /* Match found */
+                       return 1;
+       }
+       return 0;
+}
+
 static void die(char *fmt, ...)
 {
        va_list ap;
@@ -359,9 +386,8 @@ static void print_absolute_symbols(void)
 
 static void print_absolute_relocs(void)
 {
-       int i;
-       printf("Absolute relocations\n");
-       printf("Offset     Info     Type     Sym.Value Sym.Name\n");
+       int i, printed = 0;
+
        for(i = 0; i < ehdr.e_shnum; i++) {
                char *sym_strtab;
                Elf32_Sym *sh_symtab;
@@ -387,6 +413,31 @@ static void print_absolute_relocs(void)
                        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_safe_abs_reloc(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,
@@ -395,7 +446,9 @@ static void print_absolute_relocs(void)
                                name);
                }
        }
-       printf("\n");
+
+       if (printed)
+               printf("\n");
 }
 
 static void walk_relocs(void (*visit)(Elf32_Rel *rel, Elf32_Sym *sym))
@@ -508,25 +561,31 @@ static void emit_relocs(int as_text)
 
 static void usage(void)
 {
-       die("i386_reloc [--abs | --text] vmlinux\n");
+       die("relocs [--abs-syms |--abs-relocs | --text] vmlinux\n");
 }
 
 int main(int argc, char **argv)
 {
-       int show_absolute;
+       int show_absolute_syms, show_absolute_relocs;
        int as_text;
        const char *fname;
        FILE *fp;
        int i;
 
-       show_absolute = 0;
+       show_absolute_syms = 0;
+       show_absolute_relocs = 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;
+                       if (strcmp(argv[1], "--abs-syms") == 0) {
+                               show_absolute_syms = 1;
+                               continue;
+                       }
+
+                       if (strcmp(argv[1], "--abs-relocs") == 0) {
+                               show_absolute_relocs = 1;
                                continue;
                        }
                        else if (strcmp(argv[1], "--text") == 0) {
@@ -553,8 +612,11 @@ int main(int argc, char **argv)
        read_strtabs(fp);
        read_symtabs(fp);
        read_relocs(fp);
-       if (show_absolute) {
+       if (show_absolute_syms) {
                print_absolute_symbols();
+               return 0;
+       }
+       if (show_absolute_relocs) {
                print_absolute_relocs();
                return 0;
        }