linux-kernel - [PATCH 3.12 116/155] powerpc: Fix sys_call_table declaration to enable syscall tracing

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Message-Id: <abe90d6a71d2665c7198fdf538b1f64c5a0e1dce.1428411004.git.jslaby@suse.cz>
Date:	Tue,  7 Apr 2015 14:51:25 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Romeo Cane <romeo.cane.ext@...iant.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 116/155] powerpc: Fix sys_call_table declaration to enable syscall tracing

From: Romeo Cane <romeo.cane.ext@...iant.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 1028ccf560b97adbf272381a61a67e17d44d1054 upstream.

Declaring sys_call_table as a pointer causes the compiler to generate
the wrong lookup code in arch_syscall_addr().

     <arch_syscall_addr>:
        lis     r9,-16384
        rlwinm  r3,r3,2,0,29
  -     lwz     r11,30640(r9)
  -     lwzx    r3,r11,r3
  +     addi    r9,r9,30640
  +     lwzx    r3,r9,r3
        blr

The actual sys_call_table symbol, declared in assembler, is an
array. If we lie about that to the compiler we get the wrong code
generated, as above.

This definition seems only to be used by the syscall tracing code in
kernel/trace/trace_syscalls.c. With this patch I can successfully use
the syscall tracepoints:

  bash-3815  [002] ....   333.239082: sys_write -> 0x2
  bash-3815  [002] ....   333.239087: sys_dup2(oldfd: a, newfd: 1)
  bash-3815  [002] ....   333.239088: sys_dup2 -> 0x1
  bash-3815  [002] ....   333.239092: sys_fcntl(fd: a, cmd: 1, arg: 0)
  bash-3815  [002] ....   333.239093: sys_fcntl -> 0x1
  bash-3815  [002] ....   333.239094: sys_close(fd: a)
  bash-3815  [002] ....   333.239094: sys_close -> 0x0

Signed-off-by: Romeo Cane <romeo.cane.ext@...iant.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/powerpc/include/asm/syscall.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
index b54b2add07be..528ba9d8eed5 100644
--- a/arch/powerpc/include/asm/syscall.h
+++ b/arch/powerpc/include/asm/syscall.h
@@ -17,7 +17,7 @@
 
 /* ftrace syscalls requires exporting the sys_call_table */
 #ifdef CONFIG_FTRACE_SYSCALLS
-extern const unsigned long *sys_call_table;
+extern const unsigned long sys_call_table[];
 #endif /* CONFIG_FTRACE_SYSCALLS */
 
 static inline long syscall_get_nr(struct task_struct *task,
-- 
2.3.4

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