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Subject[PATCH 1/6] kbuild: Remove relocations from kallsyms table
Date
Remove the ELF relocations from the kallsyms_address[] table.
Instead we just store offsets to _text and relocate that while
accessing the kallsyms table. This is done with a new
kallsyms_offsets[] table. With these changes .tmp_kallsyms*.o
becomes relocation free.

In theory this would also allow to shrink the kallsyms table
on 64bit by using offsets.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
kernel/kallsyms.c | 27 ++++++++++++++++-----------
scripts/kallsyms.c | 18 ++++++------------
2 files changed, 22 insertions(+), 23 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 3127ad5..e7d7844 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -36,7 +36,7 @@
* These will be re-linked against their real values
* during the second link stage.
*/
-extern const unsigned long kallsyms_addresses[] __attribute__((weak));
+extern const long kallsyms_offsets[] __attribute__((weak));
extern const u8 kallsyms_names[] __attribute__((weak));

/*
@@ -51,6 +51,11 @@ extern const u16 kallsyms_token_index[] __attribute__((weak));

extern const unsigned long kallsyms_markers[] __attribute__((weak));

+static inline unsigned long kallsyms_address(int ind)
+{
+ return (unsigned long)RELOC_HIDE(&_text, kallsyms_offsets[ind]);
+}
+
static inline int is_kernel_inittext(unsigned long addr)
{
if (addr >= (unsigned long)_sinittext
@@ -186,7 +191,7 @@ 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_address(i);
}
return module_kallsyms_lookup_name(name);
}
@@ -203,7 +208,7 @@ 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_address(i));
if (ret != 0)
return ret;
}
@@ -219,15 +224,15 @@ 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);
+ BUG_ON(!kallsyms_offsets);

- /* Do a binary search on the sorted kallsyms_addresses array. */
+ /* Do a binary search on the sorted kallsyms_offsets array. */
low = 0;
high = kallsyms_num_syms;

while (high - low > 1) {
mid = low + (high - low) / 2;
- if (kallsyms_addresses[mid] <= addr)
+ if (kallsyms_address(mid) <= addr)
low = mid;
else
high = mid;
@@ -237,15 +242,15 @@ 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_address(low - 1) == kallsyms_address(low))
--low;

- symbol_start = kallsyms_addresses[low];
+ symbol_start = kallsyms_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_address(i) > symbol_start) {
+ symbol_end = kallsyms_address(i);
break;
}
}
@@ -469,7 +474,7 @@ 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_address(iter->pos);

iter->type = kallsyms_get_symbol_type(off);

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 10085de..56f5986 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -190,7 +190,7 @@ static int symbol_valid(struct sym_entry *s)
* specified so exclude them to get a stable symbol list.
*/
static char *special_symbols[] = {
- "kallsyms_addresses",
+ "kallsyms_offsets",
"kallsyms_num_syms",
"kallsyms_names",
"kallsyms_markers",
@@ -322,19 +322,13 @@ static void write_src(void)
* symbols that are declared static and are private to their
* .o files. This prevents .tmp_kallsyms.o or any other
* object from referencing them.
+ *
+ * We do the offsets to _text now in kallsyms.c at runtime,
+ * to get a relocationless symbol table.
*/
- output_label("kallsyms_addresses");
+ output_label("kallsyms_offsets");
for (i = 0; i < table_cnt; i++) {
- if (toupper(table[i].sym[0]) != 'A') {
- if (_text <= table[i].addr)
- printf("\tPTR\t_text + %#llx\n",
- table[i].addr - _text);
- else
- printf("\tPTR\t_text - %#llx\n",
- _text - table[i].addr);
- } else {
- printf("\tPTR\t%#llx\n", table[i].addr);
- }
+ printf("\tPTR\t%#llx\n", table[i].addr - _text);
}
printf("\n");

--
1.8.5.2


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