[PATCH 4/6] ftrace syscalls: Allow arch specific syscall symbol matching

[Ian Munsie]

From: Ian Munsie <imunsie at au1.ibm.com>

Some architectures have unusual symbol names and the generic code to
match the symbol name with the function name for the syscall metadata
will fail. For example, symbols on PPC64 start with a period and the
generic code will fail to match them.

This patch moves the match logic out into a separate function which an
arch can override by defining ARCH_HAS_SYSCALL_MATCH_SYM_NAME in
asm/ftrace.h and implementing arch_syscall_match_sym_name.

Signed-off-by: Ian Munsie <imunsie at au1.ibm.com>
---
 Documentation/trace/ftrace-design.txt |    4 ++++
 kernel/trace/trace_syscalls.c         |   21 ++++++++++++++-------
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/Documentation/trace/ftrace-design.txt b/Documentation/trace/ftrace-design.txt
index 6fca17b..79fcafc 100644
--- a/Documentation/trace/ftrace-design.txt
+++ b/Documentation/trace/ftrace-design.txt
@@ -250,6 +250,10 @@ You need very few things to get the syscalls tracing in an arch.
 - If the system call table on this arch is more complicated than a simple array
   of addresses of the system calls, implement an arch_syscall_addr to return
   the address of a given system call.
+- If the symbol names of the system calls do not match the function names on
+  this arch, define ARCH_HAS_SYSCALL_MATCH_SYM_NAME in asm/ftrace.h and
+  implement arch_syscall_match_sym_name with the appropriate logic to return
+  true if the function name corresponds with the symbol name.
 - Tag this arch as HAVE_SYSCALL_TRACEPOINTS.
 
 
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 33360b9..7b76a65 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -60,6 +60,19 @@ extern unsigned long __stop_syscalls_metadata[];
 
 static struct syscall_metadata **syscalls_metadata;
 
+#ifndef ARCH_HAS_SYSCALL_MATCH_SYM_NAME
+static inline bool arch_syscall_match_sym_name(const char *sym, const char *name)
+{
+	/*
+	 * Only compare after the "sys" prefix. Archs that use
+	 * syscall wrappers may have syscalls symbols aliases prefixed
+	 * with "SyS" instead of "sys", leading to an unwanted
+	 * mismatch.
+	 */
+	return !strcmp(sym + 3, name + 3);
+}
+#endif
+
 static struct syscall_metadata *find_syscall_meta(unsigned long syscall)
 {
 	struct syscall_metadata *start;
@@ -72,13 +85,7 @@ static struct syscall_metadata *find_syscall_meta(unsigned long syscall)
 	kallsyms_lookup(syscall, NULL, NULL, NULL, str);
 
 	for ( ; start < stop; start++) {
-		/*
-		 * Only compare after the "sys" prefix. Archs that use
-		 * syscall wrappers may have syscalls symbols aliases prefixed
-		 * with "SyS" instead of "sys", leading to an unwanted
-		 * mismatch.
-		 */
-		if (start->name && !strcmp(start->name + 3, str + 3))
+		if (start->name && arch_syscall_match_sym_name(str, start->name))
 			return start;
 	}
 	return NULL;
-- 
1.7.2.3