[RFC PATCH] kernel/kallsyms.c: only show legal kernel symbol

[Ming Lei]

On Mon, 28 Oct 2013 13:44:30 +1030
Rusty Russell <rusty at rustcorp.com.au> wrote:

> Ming Lei <tom.leiming at gmail.com> writes:
> 
> I don't know...  It would be your job, as the person making the change,
> to find all the users of kallsyms and prove that.
> 
> This is why it is easier not to include incorrect values in the kernel's
> kallsyms in the first place.

OK, thanks for your comment, and I figured out one way to do it in
scripts/kallsyms.c, could you comment on below patch?

--
From 4327534dedfa60d208ac3e23db7556c243e1c7dc Mon Sep 17 00:00:00 2001
From: Ming Lei <tom.leiming at gmail.com>
Date: Mon, 28 Oct 2013 13:04:49 +0800
Subject: [PATCH] scripts/kallsyms: filter symbols not in kernel address space

This patch uses CONFIG_PAGE_OFFSET to filter symbols which
are not in kernel address space because these symbols are
generally for generating code purpose and can't be run at
kernel mode, so we needn't keep them in /proc/kallsyms.

For example, on ARM there are some symbols which may be
linked in relocatable code section, then perf can't parse
symbols any more from /proc/kallsyms, this patch fixes the
problem.

Cc: Russell King <linux at arm.linux.org.uk>
Cc: linux-arm-kernel at lists.infradead.org
Cc: Rusty Russell <rusty at rustcorp.com.au>
Cc: Michal Marek <mmarek at suse.cz>
Signed-off-by: Ming Lei <tom.leiming at gmail.com>
---
 scripts/kallsyms.c      |   12 +++++++++++-
 scripts/link-vmlinux.sh |    2 ++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 487ac6f..9a11f9f 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -55,6 +55,7 @@ static struct sym_entry *table;
 static unsigned int table_size, table_cnt;
 static int all_symbols = 0;
 static char symbol_prefix_char = '\0';
+static unsigned long long kernel_start_addr = 0;
 
 int token_profit[0x10000];
 
@@ -65,7 +66,10 @@ unsigned char best_table_len[256];
 
 static void usage(void)
 {
-	fprintf(stderr, "Usage: kallsyms [--all-symbols] [--symbol-prefix=<prefix char>] < in.map > out.S\n");
+	fprintf(stderr, "Usage: kallsyms [--all-symbols] "
+			"[--symbol-prefix=<prefix char>] "
+			"[--page-offset=<CONFIG_PAGE_OFFSET>] "
+			"< in.map > out.S\n");
 	exit(1);
 }
 
@@ -194,6 +198,9 @@ static int symbol_valid(struct sym_entry *s)
 	int i;
 	int offset = 1;
 
+	if (s->addr < kernel_start_addr)
+		return 0;
+
 	/* skip prefix char */
 	if (symbol_prefix_char && *(s->sym + 1) == symbol_prefix_char)
 		offset++;
@@ -646,6 +653,9 @@ int main(int argc, char **argv)
 				if ((*p == '"' && *(p+2) == '"') || (*p == '\'' && *(p+2) == '\''))
 					p++;
 				symbol_prefix_char = *p;
+			} else if (strncmp(argv[i], "--page-offset=", 14) == 0) {
+				const char *p = &argv[i][14];
+				kernel_start_addr = strtoull(p, NULL, 16);
 			} else
 				usage();
 		}
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 0149949..32b10f5 100644
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -82,6 +82,8 @@ kallsyms()
 		kallsymopt="${kallsymopt} --all-symbols"
 	fi
 
+	kallsymopt="${kallsymopt} --page-offset=$CONFIG_PAGE_OFFSET"
+
 	local aflags="${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL}               \
 		      ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS}"
 
-- 
1.7.9.5




Thanks,
-- 
Ming Lei