Message-ID: <20240925150059.3955569-38-ardb+git@google.com>
Date: Wed, 25 Sep 2024 17:01:08 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
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Subject: [RFC PATCH 08/28] scripts/kallsyms: Remove support for absolute
 per-CPU variables

From: Ard Biesheuvel <ardb@...nel.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@...nel.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

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