tracing/syscalls: Make arch_syscall_addr weak

Some architectures use non-trivial system call tables and will not work
with the generic arch_syscall_addr code. For example, PowerPC64 uses a
table of twin long longs.

This patch makes the generic arch_syscall_addr weak to allow
architectures with non-trivial system call tables to override it.

Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
LKML-Reference: <1296703645-18718-4-git-send-email-imunsie@au1.ibm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 4 insertions, 1 deletions

diff --git a/Documentation/trace/ftrace-design.txt b/Documentation/trace/ftrace-design.txt
index dc52bd442c92..6fca17beee2f 100644
--- a/Documentation/trace/ftrace-design.txt
+++ b/Documentation/trace/ftrace-design.txt
@@ -247,6 +247,9 @@ You need very few things to get the syscalls tracing in an arch.
 - Support the TIF_SYSCALL_TRACEPOINT thread flags.
 - Put the trace_sys_enter() and trace_sys_exit() tracepoints calls from ptrace
   in the ptrace syscalls tracing path.
+- 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.
 - Tag this arch as HAVE_SYSCALL_TRACEPOINTS.
 
 
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 423094288fb5..af831545f656 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -446,7 +446,7 @@ int init_syscall_trace(struct ftrace_event_call *call)
         return id;
 }
 
-unsigned long __init arch_syscall_addr(int nr)
+unsigned long __init __weak arch_syscall_addr(int nr)
 {
         return (unsigned long)sys_call_table[nr];
 }