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Message-ID: <20061023194041.GJ13263@in.ibm.com>
Date: Mon, 23 Oct 2006 15:40:41 -0400
From: Vivek Goyal <vgoyal@...ibm.com>
To: linux kernel mailing list <linux-kernel@...r.kernel.org>
Cc: Reloc Kernel List <fastboot@...ts.osdl.org>, ebiederm@...ssion.com,
akpm@...l.org, ak@...e.de, hpa@...or.com, magnus.damm@...il.com,
lwang@...hat.com, dzickus@...hat.com, maneesh@...ibm.com
Subject: [PATCH 9/11] 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@...ibm.com>
---
arch/i386/boot/compressed/Makefile | 2
arch/i386/boot/compressed/relocs.c | 82 ++++++++++++++++++++++++++++++++-----
2 files changed, 73 insertions(+), 11 deletions(-)
diff -puN arch/i386/boot/compressed/Makefile~i386-explicitly-warn-about-absolute-symbols-during-compile arch/i386/boot/compressed/Makefile
--- linux-2.6.19-rc2-git7-reloc/arch/i386/boot/compressed/Makefile~i386-explicitly-warn-about-absolute-symbols-during-compile 2006-10-23 13:15:21.000000000 -0400
+++ linux-2.6.19-rc2-git7-reloc-root/arch/i386/boot/compressed/Makefile 2006-10-23 13:15:21.000000000 -0400
@@ -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 -puN arch/i386/boot/compressed/relocs.c~i386-explicitly-warn-about-absolute-symbols-during-compile arch/i386/boot/compressed/relocs.c
--- linux-2.6.19-rc2-git7-reloc/arch/i386/boot/compressed/relocs.c~i386-explicitly-warn-about-absolute-symbols-during-compile 2006-10-23 13:15:21.000000000 -0400
+++ linux-2.6.19-rc2-git7-reloc-root/arch/i386/boot/compressed/relocs.c 2006-10-23 13:15:21.000000000 -0400
@@ -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;
}
_
-
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