[RFC PATCH 08/28] scripts/kallsyms: Remove support for absolute per-CPU variables

Ard Biesheuvel
2024-09-25T15:02:11Z

From: Ard Biesheuvel <ardb@kernel.org>

SMP on x86_64 no longer needs absolute per-CPU variables, so this
support can be dropped from kallsyms as well, as no other architectures
rely on this functionality.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
init/Kconfig | 4 --
kernel/kallsyms.c | 12 +----
scripts/kallsyms.c | 51 +++-----------------
scripts/link-vmlinux.sh | 4 --
4 files changed, 9 insertions(+), 62 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index be8a9a786d3c..f6eeba81282d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1835,10 +1835,6 @@ config KALLSYMS_ALL

Say N unless you really need all symbols, or kernel live patching.

-config KALLSYMS_ABSOLUTE_PERCPU
- bool
- depends on KALLSYMS
-
# end of the "standard kernel features (expert users)" menu

config ARCH_HAS_MEMBARRIER_CALLBACKS
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index a9a0ca605d4a..4198f30aac3c 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -148,16 +148,8 @@ static unsigned int get_symbol_offset(unsigned long pos)

unsigned long kallsyms_sym_address(int 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];
+ /* values are unsigned offsets */
+ return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
}

static unsigned int get_symbol_seq(int index)
diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 09757d300a05..9c34b9397872 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -5,7 +5,7 @@
* This software may be used and distributed according to the terms
* of the GNU General Public License, incorporated herein by reference.
*
- * Usage: kallsyms [--all-symbols] [--absolute-percpu] in.map > out.S
+ * Usage: kallsyms [--all-symbols] in.map > out.S
*
* Table compression uses all the unused char codes on the symbols and
* maps these to the most used substrings (tokens). For instance, it might
@@ -37,7 +37,6 @@ struct sym_entry {
unsigned long long addr;
unsigned int len;
unsigned int seq;
- bool percpu_absolute;
unsigned char sym[];
};

@@ -62,7 +61,6 @@ static struct addr_range percpu_range = {
static struct sym_entry **table;
static unsigned int table_size, table_cnt;
static int all_symbols;
-static int absolute_percpu;

static int token_profit[0x10000];

@@ -73,7 +71,7 @@ static unsigned char best_table_len[256];

static void usage(void)
{
- fprintf(stderr, "Usage: kallsyms [--all-symbols] [--absolute-percpu] in.map > out.S\n");
+ fprintf(stderr, "Usage: kallsyms [--all-symbols] in.map > out.S\n");
exit(1);
}

@@ -175,7 +173,6 @@ static struct sym_entry *read_symbol(FILE *in, char **buf, size_t *buf_len)
sym->len = len;
sym->sym[0] = type;
strcpy(sym_name(sym), name);
- sym->percpu_absolute = false;

return sym;
}
@@ -319,11 +316,6 @@ static int expand_symbol(const unsigned char *data, int len, char *result)
return total;
}

-static bool symbol_absolute(const struct sym_entry *s)
-{
- return s->percpu_absolute;
-}
-
static int compare_names(const void *a, const void *b)
{
int ret;
@@ -457,20 +449,10 @@ static void write_src(void)
long long offset;
bool 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;
- }
+ offset = table[i]->addr - relative_base;
+ overflow = (offset < 0 || offset > UINT_MAX);
if (overflow) {
- fprintf(stderr, "kallsyms failure: "
- "%s symbol value %#llx out of range in relative mode\n",
- symbol_absolute(table[i]) ? "absolute" : "relative",
+ fprintf(stderr, "kallsyms failure: symbol value %#llx out of range\n",
table[i]->addr);
exit(EXIT_FAILURE);
}
@@ -725,32 +707,16 @@ static void sort_symbols(void)
qsort(table, table_cnt, sizeof(table[0]), compare_symbols);
}

-static void make_percpus_absolute(void)
-{
- unsigned int i;
-
- for (i = 0; i < table_cnt; i++)
- if (symbol_in_range(table[i], &percpu_range, 1)) {
- /*
- * Keep the 'A' override for percpu symbols to
- * ensure consistent behavior compared to older
- * versions of this tool.
- */
- table[i]->sym[0] = 'A';
- table[i]->percpu_absolute = true;
- }
-}
-
/* find the minimum non-absolute symbol address */
static void record_relative_base(void)
{
unsigned int i;

for (i = 0; i < table_cnt; i++)
- if (table[i]->addr && !symbol_absolute(table[i])) {
+ if (table[i]->addr) {
/*
* The table is sorted by address.
- * Take the first non-absolute symbol value.
+ * Take the first non-zero symbol value.
*/
relative_base = table[i]->addr;
return;
@@ -762,7 +728,6 @@ int main(int argc, char **argv)
while (1) {
static const struct option long_options[] = {
{"all-symbols", no_argument, &all_symbols, 1},
- {"absolute-percpu", no_argument, &absolute_percpu, 1},
{},
};

@@ -779,8 +744,6 @@ int main(int argc, char **argv)

read_map(argv[optind]);
shrink_table();
- if (absolute_percpu)
- make_percpus_absolute();
sort_symbols();
record_relative_base();
optimize_token_table();
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index a9b3f34a78d2..df5f3fbb46f3 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -140,10 +140,6 @@ kallsyms()
kallsymopt="${kallsymopt} --all-symbols"
fi

- if is_enabled CONFIG_KALLSYMS_ABSOLUTE_PERCPU; then
- kallsymopt="${kallsymopt} --absolute-percpu"
- fi
-
info KSYMS "${2}.S"
scripts/kallsyms ${kallsymopt} "${1}" > "${2}.S"

--
2.46.0.792.g87dc391469-goog