Re: [PATCH 1/3] arm: include: asm: swab: mask rev16 instruction for clang

On Tue, Jul 27, 2021 at 10:53 AM Nick Desaulniers
[off-list ref] wrote:

On Tue, Jul 27, 2021 at 7:12 AM Pavo Banicevic
[off-list ref] wrote:

quoted

From: Ivan Khoronzhuk <redacted>

The samples/bpf with clang -emit-llvm reuses linux headers to build
bpf samples, and this w/a only for samples (samples/bpf/Makefile
CLANG-bpf).

It allows to build samples/bpf for arm bpf using clang.
In another way clang -emit-llvm generates errors like:

CLANG-bpf  samples/bpf/tc_l2_redirect_kern.o
<inline asm>:1:2: error: invalid register/token name
rev16 r3, r0

This decision is arguable, probably there is another way, but
it doesn't have impact on samples/bpf, so it's easier just ignore
it for clang, at least for now.

NACK

The way to fix these is to sort out the header includes, not turning
off arbitrary things that are used by the actual kernel build for 32b
ARM.

Would it be too horrible to just get rid of `clang -emit-llvm` and use
vmlinux.h (we don't need to do CO-RE, btw, just generate vmlinux.h
from the matching kernel)? Kumar has already started moving in that
direction in his recent patch set ([0]). Would that get rid of all
these issues?

  [0] https://patchwork.kernel.org/project/netdevbpf/list/?series=519281&state=*

quoted

Signed-off-by: Ivan Khoronzhuk <redacted>
---
 arch/arm/include/asm/swab.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm/include/asm/swab.h b/arch/arm/include/asm/swab.h
index c6051823048b..a9fd9cd33d5e 100644
--- a/arch/arm/include/asm/swab.h
+++ b/arch/arm/include/asm/swab.h

@@ -25,8 +25,11 @@ static inline __attribute_const__ __u32 __arch_swahb32(__u32 x)
        __asm__ ("rev16 %0, %1" : "=r" (x) : "r" (x));
        return x;
 }
+
+#ifndef __clang__
 #define __arch_swahb32 __arch_swahb32
 #define __arch_swab16(x) ((__u16)__arch_swahb32(x))
+#endif

 static inline __attribute_const__ __u32 __arch_swab32(__u32 x)
 {
--

2.32.0

--
Thanks,
~Nick Desaulniers