[PATCH 1/2] kallsyms: get rid of code for absolute kallsyms

From: Jann Horn
Date: Wed Feb 21 2024 - 15:27:16 EST

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To compile code for absolute kallsyms, you had to turn off
KALLSYMS_BASE_RELATIVE. I think based on the way it was declared in
Kconfig (without a string after "bool"), it wasn't even possible to
select it.

Get rid of this config option, as preparation for some kallsyms
optimizations that would otherwise be infeasible.

Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
---
init/Kconfig | 18 -------
kernel/crash_core.c | 4 --
kernel/kallsyms.c | 10 +---
kernel/kallsyms_internal.h | 1 -
scripts/kallsyms.c | 78 ++++++++++++-----------------
scripts/link-vmlinux.sh | 4 --
tools/perf/tests/vmlinux-kallsyms.c | 1 -
7 files changed, 34 insertions(+), 82 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 8426d59cc634..ef525aacfc4c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1791,24 +1791,6 @@ config KALLSYMS_ABSOLUTE_PERCPU
depends on KALLSYMS
default X86_64 && SMP

-config KALLSYMS_BASE_RELATIVE
- bool
- depends on KALLSYMS
- default y
- 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.
-
# end of the "standard kernel features (expert users)" menu

config ARCH_HAS_MEMBARRIER_CALLBACKS
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 75cd6a736d03..1e72e65ca344 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -817,12 +817,8 @@ static int __init crash_save_vmcoreinfo_init(void)
VMCOREINFO_SYMBOL(kallsyms_num_syms);
VMCOREINFO_SYMBOL(kallsyms_token_table);
VMCOREINFO_SYMBOL(kallsyms_token_index);
-#ifdef CONFIG_KALLSYMS_BASE_RELATIVE
VMCOREINFO_SYMBOL(kallsyms_offsets);
VMCOREINFO_SYMBOL(kallsyms_relative_base);
-#else
- VMCOREINFO_SYMBOL(kallsyms_addresses);
-#endif /* CONFIG_KALLSYMS_BASE_RELATIVE */
#endif /* CONFIG_KALLSYMS */

arch_crash_save_vmcoreinfo();
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 18edd57b5fe8..db9bd5ff6383 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -148,9 +148,6 @@ static unsigned int get_symbol_offset(unsigned long pos)

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];
@@ -326,12 +323,9 @@ static unsigned long get_symbol_pos(unsigned long addr,
unsigned long i, low, high, mid;

/* This kernel should never had been booted. */
- if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
- BUG_ON(!kallsyms_addresses);
- else
- BUG_ON(!kallsyms_offsets);
+ 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;

diff --git a/kernel/kallsyms_internal.h b/kernel/kallsyms_internal.h
index 27fabdcc40f5..451a38b88db9 100644
--- a/kernel/kallsyms_internal.h
+++ b/kernel/kallsyms_internal.h
@@ -8,7 +8,6 @@
* These will be re-linked against their real values
* during the second link stage.
*/
-extern const unsigned long kallsyms_addresses[] __weak;
extern const int kallsyms_offsets[] __weak;
extern const u8 kallsyms_names[] __weak;

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 653b92f6d4c8..f35be95adfbe 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -6,7 +6,7 @@
* of the GNU General Public License, incorporated herein by reference.
*
* Usage: kallsyms [--all-symbols] [--absolute-percpu]
- * [--base-relative] [--lto-clang] in.map > out.S
+ * [--lto-clang] 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
@@ -63,7 +63,6 @@ static struct sym_entry **table;
static unsigned int table_size, table_cnt;
static int all_symbols;
static int absolute_percpu;
-static int base_relative;
static int lto_clang;

static int token_profit[0x10000];
@@ -76,7 +75,7 @@ static unsigned char best_table_len[256];
static void usage(void)
{
fprintf(stderr, "Usage: kallsyms [--all-symbols] [--absolute-percpu] "
- "[--base-relative] [--lto-clang] in.map > out.S\n");
+ "[--lto-clang] in.map > out.S\n");
exit(1);
}

@@ -484,54 +483,43 @@ static void write_src(void)
printf("\t.short\t%d\n", best_idx[i]);
printf("\n");

- if (!base_relative)
- output_label("kallsyms_addresses");
- else
- output_label("kallsyms_offsets");
+ output_label("kallsyms_offsets");

for (i = 0; i < table_cnt; i++) {
- if (base_relative) {
- /*
- * 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.
- */
+ /*
+ * 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.
+ */

- 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 /* %s */\n", (int)offset, table[i]->sym);
- } else if (!symbol_absolute(table[i])) {
- output_address(table[i]->addr);
+ 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 {
- printf("\tPTR\t%#llx\n", table[i]->addr);
+ 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 /* %s */\n", (int)offset, table[i]->sym);
}
printf("\n");

- if (base_relative) {
- output_label("kallsyms_relative_base");
- output_address(relative_base);
- printf("\n");
- }
+ output_label("kallsyms_relative_base");
+ output_address(relative_base);
+ printf("\n");

if (lto_clang)
for (i = 0; i < table_cnt; i++)
@@ -813,7 +801,6 @@ int main(int argc, char **argv)
static const struct option long_options[] = {
{"all-symbols", no_argument, &all_symbols, 1},
{"absolute-percpu", no_argument, &absolute_percpu, 1},
- {"base-relative", no_argument, &base_relative, 1},
{"lto-clang", no_argument, &lto_clang, 1},
{},
};
@@ -834,8 +821,7 @@ int main(int argc, char **argv)
if (absolute_percpu)
make_percpus_absolute();
sort_symbols();
- if (base_relative)
- record_relative_base();
+ record_relative_base();
optimize_token_table();
write_src();

diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 7862a8101747..5127371d3393 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -157,10 +157,6 @@ kallsyms()
kallsymopt="${kallsymopt} --absolute-percpu"
fi

- if is_enabled CONFIG_KALLSYMS_BASE_RELATIVE; then
- kallsymopt="${kallsymopt} --base-relative"
- fi
-
if is_enabled CONFIG_LTO_CLANG; then
kallsymopt="${kallsymopt} --lto-clang"
fi
diff --git a/tools/perf/tests/vmlinux-kallsyms.c b/tools/perf/tests/vmlinux-kallsyms.c
index 822f893e67d5..1bb91f2ec5ba 100644
--- a/tools/perf/tests/vmlinux-kallsyms.c
+++ b/tools/perf/tests/vmlinux-kallsyms.c
@@ -26,7 +26,6 @@ static bool is_ignored_symbol(const char *name, char type)
* when --all-symbols is specified so exclude them to get a
* stable symbol list.
*/
- "kallsyms_addresses",
"kallsyms_offsets",
"kallsyms_relative_base",
"kallsyms_num_syms",
--
2.44.0.rc0.258.g7320e95886-goog

Next message: Jann Horn: "[PATCH 2/2] kallsyms: build faster by using .incbin"
Previous message: H.J. Lu: "Re: [musl] Re: [PATCH v8 00/38] arm64/gcs: Provide support for GCS in userspace"
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