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Commit 6a044b3a authored by Vivek Goyal's avatar Vivek Goyal Committed by Andi Kleen
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[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: default avatarVivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
parent 968de4f0

arch/i386/boot/compressed/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -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)

arch/i386/boot/compressed/relocs.c

+72 −10
Original line number Diff line number Diff line
@@ -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,
@@ -395,6 +446,8 @@ static void print_absolute_relocs(void) 
				name);

		}

	}



	if (printed)

		printf("\n");

}
@@ -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;

	}