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SubjectRe: [PATCH] tcp: don't use __constant_cpu_to_be32
On (03/14/19 05:42), Eric Dumazet wrote:
> > cpu_to_be32() is capable enough to detect __builtin_constant_p()
> > and to use an appropriate compile time ___constant_swahb32()
> > function.
> >
> > So we can use cpu_to_be32() instead of __constant_cpu_to_be32().
>
>
> I dunno, this is uapi, this might break user space for some funky compiler ?
> I do not even know if cpu_to_be32() _is_ uapi.

Hmm, excellent point.

Looking at

if_pppox.h:#define PTT_EOL __cpu_to_be16(0x0000)
if_pppox.h:#define PTT_SRV_NAME __cpu_to_be16(0x0101)
if_pppox.h:#define PTT_AC_NAME __cpu_to_be16(0x0102)
if_pppox.h:#define PTT_HOST_UNIQ __cpu_to_be16(0x0103)
if_pppox.h:#define PTT_AC_COOKIE __cpu_to_be16(0x0104)
if_pppox.h:#define PTT_VENDOR __cpu_to_be16(0x0105)
if_pppox.h:#define PTT_RELAY_SID __cpu_to_be16(0x0110)
if_pppox.h:#define PTT_SRV_ERR __cpu_to_be16(0x0201)
if_pppox.h:#define PTT_SYS_ERR __cpu_to_be16(0x0202)
if_pppox.h:#define PTT_GEN_ERR __cpu_to_be16(0x0203)
if_tunnel.h:#define GRE_CSUM __cpu_to_be16(0x8000)
if_tunnel.h:#define GRE_ROUTING __cpu_to_be16(0x4000)
if_tunnel.h:#define GRE_KEY __cpu_to_be16(0x2000)
if_tunnel.h:#define GRE_SEQ __cpu_to_be16(0x1000)
if_tunnel.h:#define GRE_STRICT __cpu_to_be16(0x0800)
if_tunnel.h:#define GRE_REC __cpu_to_be16(0x0700)
if_tunnel.h:#define GRE_ACK __cpu_to_be16(0x0080)
if_tunnel.h:#define GRE_FLAGS __cpu_to_be16(0x0078)
if_tunnel.h:#define GRE_VERSION __cpu_to_be16(0x0007)
if_tunnel.h:#define GRE_VERSION_0 __cpu_to_be16(0x0000)
if_tunnel.h:#define GRE_VERSION_1 __cpu_to_be16(0x0001)
if_tunnel.h:#define GRE_PROTO_PPP __cpu_to_be16(0x880b)

You are right, probably would need __cpu_to_be32, which also does
the constant folding.

=-=-=-=-=

Subject: [PATCH] tcp: don't use __constant_cpu_to_be32

__cpu_to_be32() can detect __builtin_constant_p() at compile time.
So we can use __cpu_to_be32() instead of __constant_cpu_to_be32().

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
include/uapi/linux/tcp.h | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
index 8bb6cc5f3235..cf9c246a59c8 100644
--- a/include/uapi/linux/tcp.h
+++ b/include/uapi/linux/tcp.h
@@ -70,16 +70,16 @@ union tcp_word_hdr {
#define tcp_flag_word(tp) ( ((union tcp_word_hdr *)(tp))->words [3])

enum {
- TCP_FLAG_CWR = __constant_cpu_to_be32(0x00800000),
- TCP_FLAG_ECE = __constant_cpu_to_be32(0x00400000),
- TCP_FLAG_URG = __constant_cpu_to_be32(0x00200000),
- TCP_FLAG_ACK = __constant_cpu_to_be32(0x00100000),
- TCP_FLAG_PSH = __constant_cpu_to_be32(0x00080000),
- TCP_FLAG_RST = __constant_cpu_to_be32(0x00040000),
- TCP_FLAG_SYN = __constant_cpu_to_be32(0x00020000),
- TCP_FLAG_FIN = __constant_cpu_to_be32(0x00010000),
- TCP_RESERVED_BITS = __constant_cpu_to_be32(0x0F000000),
- TCP_DATA_OFFSET = __constant_cpu_to_be32(0xF0000000)
+ TCP_FLAG_CWR = __cpu_to_be32(0x00800000),
+ TCP_FLAG_ECE = __cpu_to_be32(0x00400000),
+ TCP_FLAG_URG = __cpu_to_be32(0x00200000),
+ TCP_FLAG_ACK = __cpu_to_be32(0x00100000),
+ TCP_FLAG_PSH = __cpu_to_be32(0x00080000),
+ TCP_FLAG_RST = __cpu_to_be32(0x00040000),
+ TCP_FLAG_SYN = __cpu_to_be32(0x00020000),
+ TCP_FLAG_FIN = __cpu_to_be32(0x00010000),
+ TCP_RESERVED_BITS = __cpu_to_be32(0x0F000000),
+ TCP_DATA_OFFSET = __cpu_to_be32(0xF0000000)
};

/*
--
2.21.0
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