The patch titled
i386: warn upon absolute relocations being present
has been added to the -mm tree. Its filename is
i386-warn-upon-absolute-relocations-being-present.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: i386: warn upon absolute relocations being present
From: Vivek Goyal <vgoyal@xxxxxxxxxx>
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.
These relocations get introduced either due to linker optimizations or some
programming oversights.
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@xxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
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-warn-upon-absolute-relocations-being-present arch/i386/boot/compressed/Makefile
--- a/arch/i386/boot/compressed/Makefile~i386-warn-upon-absolute-relocations-being-present
+++ a/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 -puN arch/i386/boot/compressed/relocs.c~i386-warn-upon-absolute-relocations-being-present arch/i386/boot/compressed/relocs.c
--- a/arch/i386/boot/compressed/relocs.c~i386-warn-upon-absolute-relocations-being-present
+++ a/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;
}
_
Patches currently in -mm which might be from vgoyal@xxxxxxxxxx are
i386-distinguish-absolute-symbols.patch
i386-remove-unnecessary-align-in-vmlinuxldss.patch
i386-force-data-segment-to-be-4k-aligned.patch
i386-define-__pa_symbol.patch
i386-reserve-kernel-memory-starting-from-_text.patch
i386-config_physical_start-cleanup.patch
i386-kallsyms-generate-relocatable-symbols.patch
i386-relocatable-kernel-support.patch
i386-warn-upon-absolute-relocations-being-present.patch
i386-implement-config_physical_align.patch
i386-extend-bzimage-protocol-for-relocatable-protected-mode-kernel.patch
-
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
