diff --git a/init/Kconfig b/init/Kconfig
index b17824a875fa67c212996b2fca4565e03daba7ac..fd664b3ab99ef79432643ab3e954943e759f81ca 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1424,6 +1424,24 @@ config KALLSYMS_ABSOLUTE_PERCPU
bool
default X86_64 && SMP
+config KALLSYMS_BASE_RELATIVE
+ bool
+ depends on KALLSYMS
+ default !IA64 && !(TILE && 64BIT)
+ help
+ Instead of emitting them as absolute values in the native word size,
+ emit the symbol references in the kallsyms table as 32-bit entries,
+ each containing a relative value in the range [base, base + U32_MAX]
+ or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
+ an absolute value in the range [0, S32_MAX] or a relative value in the
+ range [base, base + S32_MAX], where base is the lowest relative symbol
+ address encountered in the image.
+
+ On 64-bit builds, this reduces the size of the address table by 50%,
+ but more importantly, it results in entries whose values are build
+ time constants, and no relocation pass is required at runtime to fix
+ up the entries based on the runtime load address of the kernel.
+
config PRINTK
default y
bool "Enable support for printk" if EXPERT
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 5c5987f1081964109f96cd6cc52b285b948f0a9e..fafd1a3ef0da56c6887fb5edd631e8e4a925a0e4 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -38,6 +38,7 @@
* during the second link stage.
*/
extern const unsigned long kallsyms_addresses[] __weak;
+extern const int kallsyms_offsets[] __weak;
extern const u8 kallsyms_names[] __weak;
/*
@@ -47,6 +48,9 @@ extern const u8 kallsyms_names[] __weak;
extern const unsigned long kallsyms_num_syms
__attribute__((weak, section(".rodata")));
+extern const unsigned long kallsyms_relative_base
+__attribute__((weak, section(".rodata")));
+
extern const u8 kallsyms_token_table[] __weak;
extern const u16 kallsyms_token_index[] __weak;
@@ -176,6 +180,23 @@ static unsigned int get_symbol_offset(unsigned long pos)
return name - kallsyms_names;
}
+static unsigned long kallsyms_sym_address(int idx)
+{
+ if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
+ return kallsyms_addresses[idx];
+
+ /* values are unsigned offsets if --absolute-percpu is not in effect */
+ if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
+ return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
+
+ /* ...otherwise, positive offsets are absolute values */
+ if (kallsyms_offsets[idx] >= 0)
+ return kallsyms_offsets[idx];
+
+ /* ...and negative offsets are relative to kallsyms_relative_base - 1 */
+ return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
+}
+
/* Lookup the address for this symbol. Returns 0 if not found. */
unsigned long kallsyms_lookup_name(const char *name)
{
@@ -187,7 +208,7 @@ unsigned long kallsyms_lookup_name(const char *name)
off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
if (strcmp(namebuf, name) == 0)
- return kallsyms_addresses[i];
+ return kallsyms_sym_address(i);
}
return module_kallsyms_lookup_name(name);
}
@@ -204,7 +225,7 @@ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
- ret = fn(data, namebuf, NULL, kallsyms_addresses[i]);
+ ret = fn(data, namebuf, NULL, kallsyms_sym_address(i));
if (ret != 0)
return ret;
}
@@ -220,7 +241,10 @@ static unsigned long get_symbol_pos(unsigned long addr,
unsigned long i, low, high, mid;
/* This kernel should never had been booted. */
- BUG_ON(!kallsyms_addresses);
+ if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
+ BUG_ON(!kallsyms_addresses);
+ else
+ BUG_ON(!kallsyms_offsets);
/* Do a binary search on the sorted kallsyms_addresses array. */
low = 0;
@@ -228,7 +252,7 @@ static unsigned long get_symbol_pos(unsigned long addr,
while (high - low > 1) {
mid = low + (high - low) / 2;
- if (kallsyms_addresses[mid] <= addr)
+ if (kallsyms_sym_address(mid) <= addr)
low = mid;
else
high = mid;
@@ -238,15 +262,15 @@ static unsigned long get_symbol_pos(unsigned long addr,
* Search for the first aliased symbol. Aliased
* symbols are symbols with the same address.
*/
- while (low && kallsyms_addresses[low-1] == kallsyms_addresses[low])
+ while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low))
--low;
- symbol_start = kallsyms_addresses[low];
+ symbol_start = kallsyms_sym_address(low);
/* Search for next non-aliased symbol. */
for (i = low + 1; i < kallsyms_num_syms; i++) {
- if (kallsyms_addresses[i] > symbol_start) {
- symbol_end = kallsyms_addresses[i];
+ if (kallsyms_sym_address(i) > symbol_start) {
+ symbol_end = kallsyms_sym_address(i);
break;
}
}
@@ -470,7 +494,7 @@ static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
unsigned off = iter->nameoff;
iter->module_name[0] = '\0';
- iter->value = kallsyms_addresses[iter->pos];
+ iter->value = kallsyms_sym_address(iter->pos);
iter->type = kallsyms_get_symbol_type(off);
diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index d39a1eeb080e25d77006ca76172991919242b41e..638b143ee60f4246cc16d67936bc62095a66c646 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -22,6 +22,7 @@
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
+#include <limits.h>
#ifndef ARRAY_SIZE
#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
@@ -43,6 +44,7 @@ struct addr_range {
};
static unsigned long long _text;
+static unsigned long long relative_base;
static struct addr_range text_ranges[] = {
{ "_stext", "_etext" },
{ "_sinittext", "_einittext" },
@@ -62,6 +64,7 @@ static int all_symbols = 0;
static int absolute_percpu = 0;
static char symbol_prefix_char = '\0';
static unsigned long long kernel_start_addr = 0;
+static int base_relative = 0;
int token_profit[0x10000];
@@ -75,7 +78,7 @@ static void usage(void)
fprintf(stderr, "Usage: kallsyms [--all-symbols] "
"[--symbol-prefix=<prefix char>] "
"[--page-offset=<CONFIG_PAGE_OFFSET>] "
- "< in.map > out.S\n");
+ "[--base-relative] < in.map > out.S\n");
exit(1);
}
@@ -205,6 +208,8 @@ static int symbol_valid(struct sym_entry *s)
*/
static char *special_symbols[] = {
"kallsyms_addresses",
+ "kallsyms_offsets",
+ "kallsyms_relative_base",
"kallsyms_num_syms",
"kallsyms_names",
"kallsyms_markers",
@@ -349,16 +354,48 @@ static void write_src(void)
printf("\t.section .rodata, \"a\"\n");
- /* Provide proper symbols relocatability by their '_text'
- * relativeness. The symbol names cannot be used to construct
- * normal symbol references as the list of symbols contains
- * symbols that are declared static and are private to their
- * .o files. This prevents .tmp_kallsyms.o or any other
- * object from referencing them.
+ /* Provide proper symbols relocatability by their relativeness
+ * to a fixed anchor point in the runtime image, either '_text'
+ * for absolute address tables, in which case the linker will
+ * emit the final addresses at build time. Otherwise, use the
+ * offset relative to the lowest value encountered of all relative
+ * symbols, and emit non-relocatable fixed offsets that will be fixed
+ * up at runtime.
+ *
+ * The symbol names cannot be used to construct normal symbol
+ * references as the list of symbols contains symbols that are
+ * declared static and are private to their .o files. This prevents
+ * .tmp_kallsyms.o or any other object from referencing them.
*/
- output_label("kallsyms_addresses");
+ if (!base_relative)
+ output_label("kallsyms_addresses");
+ else
+ output_label("kallsyms_offsets");
+
for (i = 0; i < table_cnt; i++) {
- if (!symbol_absolute(&table[i])) {
+ if (base_relative) {
+ long long offset;
+ int overflow;
+
+ if (!absolute_percpu) {
+ offset = table[i].addr - relative_base;
+ overflow = (offset < 0 || offset > UINT_MAX);
+ } else if (symbol_absolute(&table[i])) {
+ offset = table[i].addr;
+ overflow = (offset < 0 || offset > INT_MAX);
+ } else {
+ offset = relative_base - table[i].addr - 1;
+ overflow = (offset < INT_MIN || offset >= 0);
+ }
+ if (overflow) {
+ fprintf(stderr, "kallsyms failure: "
+ "%s symbol value %#llx out of range in relative mode\n",
+ symbol_absolute(&table[i]) ? "absolute" : "relative",
+ table[i].addr);
+ exit(EXIT_FAILURE);
+ }
+ printf("\t.long\t%#x\n", (int)offset);
+ } else if (!symbol_absolute(&table[i])) {
if (_text <= table[i].addr)
printf("\tPTR\t_text + %#llx\n",
table[i].addr - _text);
@@ -371,6 +408,12 @@ static void write_src(void)
}
printf("\n");
+ if (base_relative) {
+ output_label("kallsyms_relative_base");
+ printf("\tPTR\t_text - %#llx\n", _text - relative_base);
+ printf("\n");
+ }
+
output_label("kallsyms_num_syms");
printf("\tPTR\t%d\n", table_cnt);
printf("\n");
@@ -695,6 +738,18 @@ static void make_percpus_absolute(void)
}
}
+/* find the minimum non-absolute symbol address */
+static void record_relative_base(void)
+{
+ unsigned int i;
+
+ relative_base = -1ULL;
+ for (i = 0; i < table_cnt; i++)
+ if (!symbol_absolute(&table[i]) &&
+ table[i].addr < relative_base)
+ relative_base = table[i].addr;
+}
+
int main(int argc, char **argv)
{
if (argc >= 2) {
@@ -713,7 +768,9 @@ int main(int argc, char **argv)
} else if (strncmp(argv[i], "--page-offset=", 14) == 0) {
const char *p = &argv[i][14];
kernel_start_addr = strtoull(p, NULL, 16);
- } else
+ } else if (strcmp(argv[i], "--base-relative") == 0)
+ base_relative = 1;
+ else
usage();
}
} else if (argc != 1)
@@ -722,6 +779,8 @@ int main(int argc, char **argv)
read_map(stdin);
if (absolute_percpu)
make_percpus_absolute();
+ if (base_relative)
+ record_relative_base();
sort_symbols();
optimize_token_table();
write_src();
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 7a08bf9a95766b366d086d266dc3477a6035969c..453ede9d2f3db672e9f36f62c7edbf1bc58f9e3b 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -90,6 +90,10 @@ kallsyms()
kallsymopt="${kallsymopt} --absolute-percpu"
fi
+ if [ -n "${CONFIG_KALLSYMS_BASE_RELATIVE}" ]; then
+ kallsymopt="${kallsymopt} --base-relative"
+ fi
+
local aflags="${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} \
${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS}"
diff --git a/scripts/namespace.pl b/scripts/namespace.pl
index a71be6b7cdec5b11a8644132f75819941dd2d3c7..9f3c9d47a4a5d89c4e95de825f67d84b0258f0df 100755
--- a/scripts/namespace.pl
+++ b/scripts/namespace.pl
@@ -117,6 +117,8 @@ my %nameexception = (
'kallsyms_names' => 1,
'kallsyms_num_syms' => 1,
'kallsyms_addresses'=> 1,
+ 'kallsyms_offsets' => 1,
+ 'kallsyms_relative_base'=> 1,
'__this_module' => 1,
'_etext' => 1,
'_edata' => 1,