Re: [RESEND PATCH v2] bus: arm-cci: use asm unreachable

From: Robin Murphy
Date: Tue May 08 2018 - 08:19:41 EST

On 08/05/18 12:32, Stefan Agner wrote:
Mixing asm and C code is not recommended in a naked function by
gcc and leads to an error when using clang:
drivers/bus/arm-cci.c:2107:2: error: non-ASM statement in naked
function is not supported

While the function is marked __naked it actually properly return
in asm. There is no need for the unreachable() call.

The commit title is a bit out-of-date now (I guess it could just be something like "remove unnecessary unreachable()" now), but the rest looks OK to me - even GCC clearly doesn't expect anything beyond the asm to be reachable anyway since the lack of epilogue includes the lack of any compiler-generated return. I've checked that GCC 7.2 generates identical object files before and after, other than (for obvious reasons) the line numbers generated by WANT_WARN_ON_SLOWPATH for all the WARN()s appearing later in the file.

Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>

Suggested-by: Russell King <linux@xxxxxxxxxxxxxxxx>
Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
Acked-by: Nicolas Pitre <nico@xxxxxxxxxx>
drivers/bus/arm-cci.c | 2 --
1 file changed, 2 deletions(-)

diff --git a/drivers/bus/arm-cci.c b/drivers/bus/arm-cci.c
index 443e4c3fd357..b8184a903583 100644
--- a/drivers/bus/arm-cci.c
+++ b/drivers/bus/arm-cci.c
@@ -371,8 +371,6 @@ asmlinkage void __naked cci_enable_port_for_self(void)
[sizeof_struct_cpu_port] "i" (sizeof(struct cpu_port)),
[sizeof_struct_ace_port] "i" (sizeof(struct cci_ace_port)),
[offsetof_port_phys] "i" (offsetof(struct cci_ace_port, phys)) );
- unreachable();