linux-kernel - [PATCH v2 53/59] kallsyms: Take callthunks into account

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Date:   Fri, 02 Sep 2022 15:07:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Johannes Wikner <kwikner@...z.ch>,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Jann Horn <jannh@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>,
        Joao Moreira <joao.moreira@...el.com>,
        Joseph Nuzman <joseph.nuzman@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juergen Gross <jgross@...e.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH v2 53/59] kallsyms: Take callthunks into account

From: Peter Zijlstra <peterz@...radead.org>

Since the pre-symbol function padding is an integral part of the
symbol make kallsyms report it as part of the symbol by reporting it
as sym-x instead of prev_sym+y.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/kallsyms.c |   45 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 40 insertions(+), 5 deletions(-)

--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -292,6 +292,12 @@ static unsigned long get_symbol_pos(unsi
 	return low;
 }
 
+#ifdef CONFIG_FUNCTION_PADDING_BYTES
+#define PADDING_BYTES	CONFIG_FUNCTION_PADDING_BYTES
+#else
+#define PADDING_BYTES	0
+#endif
+
 /*
  * Lookup an address but don't bother to find any names.
  */
@@ -299,13 +305,25 @@ int kallsyms_lookup_size_offset(unsigned
 				unsigned long *offset)
 {
 	char namebuf[KSYM_NAME_LEN];
+	int ret;
+
+	addr += PADDING_BYTES;
 
 	if (is_ksym_addr(addr)) {
 		get_symbol_pos(addr, symbolsize, offset);
-		return 1;
+		ret = 1;
+		goto found;
 	}
-	return !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf) ||
-	       !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
+
+	ret = !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf);
+	if (!ret) {
+		ret = !!__bpf_address_lookup(addr, symbolsize,
+					     offset, namebuf);
+	}
+found:
+	if (ret && offset)
+		*offset -= PADDING_BYTES;
+	return ret;
 }
 
 static const char *kallsyms_lookup_buildid(unsigned long addr,
@@ -318,6 +336,8 @@ static const char *kallsyms_lookup_build
 	namebuf[KSYM_NAME_LEN - 1] = 0;
 	namebuf[0] = 0;
 
+	addr += PADDING_BYTES;
+
 	if (is_ksym_addr(addr)) {
 		unsigned long pos;
 
@@ -347,6 +367,8 @@ static const char *kallsyms_lookup_build
 
 found:
 	cleanup_symbol_name(namebuf);
+	if (ret && offset)
+		*offset -= PADDING_BYTES;
 	return ret;
 }
 
@@ -373,6 +395,8 @@ int lookup_symbol_name(unsigned long add
 	symname[0] = '\0';
 	symname[KSYM_NAME_LEN - 1] = '\0';
 
+	addr += PADDING_BYTES;
+
 	if (is_ksym_addr(addr)) {
 		unsigned long pos;
 
@@ -400,6 +424,8 @@ int lookup_symbol_attrs(unsigned long ad
 	name[0] = '\0';
 	name[KSYM_NAME_LEN - 1] = '\0';
 
+	addr += PADDING_BYTES;
+
 	if (is_ksym_addr(addr)) {
 		unsigned long pos;
 
@@ -416,6 +442,8 @@ int lookup_symbol_attrs(unsigned long ad
 		return res;
 
 found:
+	if (offset)
+		*offset -= PADDING_BYTES;
 	cleanup_symbol_name(name);
 	return 0;
 }
@@ -441,8 +469,15 @@ static int __sprint_symbol(char *buffer,
 	len = strlen(buffer);
 	offset -= symbol_offset;
 
-	if (add_offset)
-		len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
+	if (add_offset) {
+		char s = '+';
+
+		if ((long)offset < 0) {
+			s = '-';
+			offset = 0UL - offset;
+		}
+		len += sprintf(buffer + len, "%c%#lx/%#lx", s, offset, size);
+	}
 
 	if (modname) {
 		len += sprintf(buffer + len, " [%s", modname);