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[PATCH] i386: Warn upon absolute relocations being present

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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>
This commit is contained in:
Vivek Goyal 2006-12-07 02:14:04 +01:00 committed by Andi Kleen
parent 968de4f026
commit 6a044b3a0a
2 changed files with 73 additions and 11 deletions
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2
arch/i386/boot/compressed/Makefile
View file

@ -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)

82
arch/i386/boot/compressed/relocs.c
View file

@ -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;
}