Subject: kernel: add a config option for keeping the kallsyms table uncompressed, saving ~9kb kernel size after lzma on ar71xx
From: Felix Fietkau <[email-masked]>

[[email-masked]: added to my upstream queue 30.12.2016]
lede-commit: e0e3509b5ce2ccf93d4d67ea907613f5f7ec2eed
Signed-off-by: Felix Fietkau <[email-masked]>
---
 init/Kconfig            | 11 +++++++++++
 kernel/kallsyms.c       |  8 ++++++++
 scripts/kallsyms.c      | 12 ++++++++++++
 scripts/link-vmlinux.sh |  4 ++++
 4 files changed, 35 insertions(+)

--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1278,6 +1278,17 @@ config SYSCTL_ARCH_UNALIGN_ALLOW
 	  the unaligned access emulation.
 	  see arch/parisc/kernel/unaligned.c for reference
 
+config KALLSYMS_UNCOMPRESSED
+	bool "Keep kallsyms uncompressed"
+	depends on KALLSYMS
+	help
+		Normally kallsyms contains compressed symbols (using a token table),
+		reducing the uncompressed kernel image size. Keeping the symbol table
+		uncompressed significantly improves the size of this part in compressed
+		kernel images.
+
+		Say N unless you need compressed kernel images to be small.
+
 config HAVE_PCSPKR_PLATFORM
 	bool
 
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -75,6 +75,11 @@ static unsigned int kallsyms_expand_symb
 	 * For every byte on the compressed symbol data, copy the table
 	 * entry for that byte.
 	 */
+#ifdef CONFIG_KALLSYMS_UNCOMPRESSED
+	memcpy(result, data + 1, len - 1);
+	result += len - 1;
+	len = 0;
+#endif
 	while (len) {
 		tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
 		data++;
@@ -107,6 +112,9 @@ tail:
  */
 static char kallsyms_get_symbol_type(unsigned int off)
 {
+#ifdef CONFIG_KALLSYMS_UNCOMPRESSED
+	return kallsyms_names[off + 1];
+#endif
 	/*
 	 * Get just the first code, look it up in the token table,
 	 * and return the first char from this token.
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -59,6 +59,7 @@ static struct addr_range percpu_range =
 static struct sym_entry *table;
 static unsigned int table_size, table_cnt;
 static int all_symbols = 0;
+static int uncompressed = 0;
 static int absolute_percpu = 0;
 static int base_relative = 0;
 
@@ -440,6 +441,9 @@ static void write_src(void)
 
 	free(markers);
 
+	if (uncompressed)
+		return;
+
 	output_label("kallsyms_token_table");
 	off = 0;
 	for (i = 0; i < 256; i++) {
@@ -500,6 +504,9 @@ static void *find_token(unsigned char *s
 {
 	int i;
 
+	if (uncompressed)
+		return NULL;
+
 	for (i = 0; i < len - 1; i++) {
 		if (str[i] == token[0] && str[i+1] == token[1])
 			return &str[i];
@@ -572,6 +579,9 @@ static void optimize_result(void)
 {
 	int i, best;
 
+	if (uncompressed)
+		return;
+
 	/* using the '\0' symbol last allows compress_symbols to use standard
 	 * fast string functions */
 	for (i = 255; i >= 0; i--) {
@@ -751,6 +761,8 @@ int main(int argc, char **argv)
 				absolute_percpu = 1;
 			else if (strcmp(argv[i], "--base-relative") == 0)
 				base_relative = 1;
+			else if (strcmp(argv[i], "--uncompressed") == 0)
+				uncompressed = 1;
 			else
 				usage();
 		}
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -160,6 +160,10 @@ kallsyms()
 		kallsymopt="${kallsymopt} --base-relative"
 	fi
 
+	if [ -n "${CONFIG_KALLSYMS_UNCOMPRESSED}" ]; then
+		kallsymopt="${kallsymopt} --uncompressed"
+	fi
+
 	local aflags="${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL}               \
 		      ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS}"