linux-kernel - [PATCH 3/6] ftrace syscalls: Make arch_syscall

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Message-Id: <1291696151-4336-4-git-send-email-imunsie@au1.ibm.com>
Date:	Tue,  7 Dec 2010 15:29:08 +1100
From:	"Ian Munsie" <imunsie@....ibm.com>
To:	Avantika Mathur <mathur@...ux.vnet.ibm.com>
Cc:	Jason Baron <jbaron@...hat.com>, Ian Munsie <imunsie@....ibm.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Mike Frysinger <vapier@...too.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/6] ftrace syscalls: Make arch_syscall_addr weak

From: Ian Munsie <imunsie@....ibm.com>

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@....ibm.com>
---
 Documentation/trace/ftrace-design.txt |    3 +++
 kernel/trace/trace_syscalls.c         |    2 +-
 2 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/Documentation/trace/ftrace-design.txt b/Documentation/trace/ftrace-design.txt
index dc52bd4..6fca17b 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 5e34b49..b31ea2d 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -447,7 +447,7 @@ 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];
 }
-- 
1.7.2.3

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