[dpdk-dev] [PATCH] test/bpf: use hton instead of __builtin_bswap
Malvika Gupta
Malvika.Gupta at arm.com
Thu Oct 25 18:59:55 CEST 2018
Hi Konstantin,
At time of upstreaming the patch, I had compiled it on Cortex-A72 and it had worked with the -I parameter. But when tried building it on x86-64, I encountered the error that you were facing. From my understanding of this problem, this is a portability issue. As you pointed out, gcc and clang implement __builtin_constant_p in a different way on x86 but that may not be true for ARM.
In such a case, to enable compilation on x86, we may want to write specific hton and ntoh functions. But this would become a tedious task because, in future, to enable compilation on other architectures besides x86 and ARM, we may have to repeat this process of writing analogs for each architecture. I think the best solution in the current scenario would be to use the -U parameter to enable compilation on x86 and later decide if we want to write a new patch with analogs for builtin hton() and ntoh().
Best,
Malvika
-----Original Message-----
From: Ananyev, Konstantin <konstantin.ananyev at intel.com>
Sent: Friday, October 19, 2018 7:17 AM
To: Malvika Gupta <Malvika.Gupta at arm.com>
Cc: dev at dpdk.org; Gavin Hu (Arm Technology China) <Gavin.Hu at arm.com>; Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>; nd <nd at arm.com>
Subject: RE: [PATCH] test/bpf: use hton instead of __builtin_bswap
Hi Malvika,
>
> Hi Konstantin,
>
> I installed the clang version 4.0.1 to check for the issue you were
> facing with -O2 compilation. I was able to compile with -O2 and -O0 optimization without any errors. Please see the exact command I used and the following output for your reference:
>
> $ clang -O2 -target bpf -I /usr/include/aarch64-linux-gnu/ -c t1.c $
> clang -O0 -target bpf -I /usr/include/aarch64-linux-gnu/ -c t1.c $
> clang -v clang version 4.0.1-10 (tags/RELEASE_401/final)
> Target: aarch64-unknown-linux-gnu
> Thread model: posix
> InstalledDir: /usr/bin
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/aarch64-linux-gnu/6
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/aarch64-linux-gnu/6.4.0
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/aarch64-linux-gnu/7
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/aarch64-linux-gnu/7.3.0
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/aarch64-linux-gnu/8
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/aarch64-linux-gnu/8.0.1
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/6
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/6.4.0
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/7
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/7.3.0
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/8
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/8.0.1
> Selected GCC installation: /usr/bin/../lib/gcc/aarch64-linux-gnu/7.3.0
> Candidate multilib: .;@m64
> Selected multilib: .;@m64
>
> I hope this was helpful to you.
Sorry for delay.
I tried with clang 6.0, but still seeing same issue.
Digging a bit more, I think the culprit is here:
#ifdef __GNUC__
# if __GNUC__ >= 2
# define __bswap_16(x) \
(__extension__ \
({ unsigned short int __v, __x = (unsigned short int) (x); \
if (__builtin_constant_p (__x)) \ <------ evaluates to FALSE !!!
__v = __bswap_constant_16 (__x); \
else \
__asm__ ("rorw $8, %w0" \
: "=r" (__v) \
: "0" (__x) \
: "cc"); \
__v; }))
# else
/* This is better than nothing. */
# define __bswap_16(x) \
(__extension__ \
({ unsigned short int __x = (unsigned short int) (x); \
__bswap_constant_16 (__x); }))
# endif
#else
static __inline unsigned short int
__bswap_16 (unsigned short int __bsx)
{
return __bswap_constant_16 (__bsx);
}
#endif
Seems that gcc and clang implements __builtin_constant_p in a different way.
Let say, the following function:
int bbb1(void) {uint16_t x=0; return__bswap_constant_16(x);} when compiled with gcc would return 1, while when compiled with clang - 0.
Adding 'const' to definition of 'x' cures the problem for clang.
I don't know why there is no 'const' in original __bswap_16() macro.
To overcome that problem, I used:
clang -O2 -U__GNUC__ -target bpf -c t1.c
Another possible option - define our own analogs for buitin hton*().
Konstantin
> Best Regards,
> Malvika Gupta
>
>
> -----Original Message-----
> From: Malvika Gupta
> Sent: Wednesday, September 5, 2018 4:43 PM
> To: Ananyev, Konstantin <konstantin.ananyev at intel.com>
> Cc: dev at dpdk.org; Gavin Hu (Arm Technology China) <Gavin.Hu at arm.com>;
> Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>; Brian Brooks
> <Brian.Brooks at arm.com>; nd <nd at arm.com>
> Subject: RE: [PATCH] test/bpf: use hton instead of __builtin_bswap
>
> Hi Ananyev,
>
> I used clang version 6.0.0. Please see the following output for your reference.
>
> $ clang -v
> clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final)
> Target: aarch64-unknown-linux-gnu
> Thread model: posix
> InstalledDir: /usr/bin
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/aarch64-linux-gnu/6
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/aarch64-linux-gnu/6.4.0
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/aarch64-linux-gnu/7
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/aarch64-linux-gnu/7.3.0
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/aarch64-linux-gnu/8
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/aarch64-linux-gnu/8.0.1
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/6
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/6.4.0
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/7
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/7.3.0
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/8
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/8.0.1
> Selected GCC installation: /usr/bin/../lib/gcc/aarch64-linux-gnu/7.3.0
> Candidate multilib: .;@m64
> Selected multilib: .;@m64
>
> Also, the code compiles with both -O2 and -O0 for me.
>
> I hope this was helpful
> Best,
> Malvika
>
> -----Original Message-----
> From: Ananyev, Konstantin <konstantin.ananyev at intel.com>
> Sent: Tuesday, September 4, 2018 8:56 AM
> To: Malvika Gupta <Malvika.Gupta at arm.com>
> Cc: dev at dpdk.org; Gavin Hu (Arm Technology China) <Gavin.Hu at arm.com>;
> Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>; Brian Brooks
> <Brian.Brooks at arm.com>; nd <nd at arm.com>
> Subject: RE: [PATCH] test/bpf: use hton instead of __builtin_bswap
>
> Hi,
>
> >
> > Convert host machine endianness to networking endianness for
> > comparison of incoming packets with BPF filter
> >
> >
> > Signed-off-by: Malvika Gupta <malvika.gupta at arm.com>
> > Reviewed-by: Gavin Hu <gavin.hu at arm.com>
> > Reviewed-by: Brian Brooks <brian.brooks at arm.com>
> > Suggested-by: Brian Brooks <brian.brooks at arm.com>
> > ---
> > test/bpf/t1.c | 7 ++++---
> > test/bpf/t3.c | 3 ++-
> > 2 files changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/test/bpf/t1.c b/test/bpf/t1.c index
> > 60f9434ab..7943fcf34
> > 100644
> > --- a/test/bpf/t1.c
> > +++ b/test/bpf/t1.c
> > @@ -28,24 +28,25 @@
> > #include <net/ethernet.h>
> > #include <netinet/ip.h>
> > #include <netinet/udp.h>
> > +#include <arpa/inet.h>
> >
> > uint64_t
> > entry(void *pkt)
> > {
> > struct ether_header *ether_header = (void *)pkt;
> >
> > - if (ether_header->ether_type != __builtin_bswap16(0x0800))
> > + if (ether_header->ether_type != htons(0x0800))
>
> Which version of clang do you use?
> With my one I get:
> $ clang -O2 -target bpf -c t1.c
> t1.c:37:34: error: couldn't allocate output register for constraint 'r'
> if (ether_header->ether_type != ntohs(0x0800))
> ^
> /usr/include/netinet/in.h:402:21: note: expanded from macro 'ntohs'
> # define ntohs(x) __bswap_16 (x)
> ^
> /usr/include/bits/byteswap-16.h:31:14: note: expanded from macro '__bswap_16'
> __asm__ ("rorw $8, %w0"
>
> With '-O0' it compiles ok.
>
> $ clang -v
> clang version 4.0.1 (tags/RELEASE_401/final)
> Target: x86_64-unknown-linux-gnu
> Thread model: posix
> InstalledDir: /usr/bin
> Found candidate GCC installation:
> /usr/bin/../lib/gcc/x86_64-redhat-linux/7
> Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/7
> Selected GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/7
> Candidate multilib: .;@m64
> Candidate multilib: 32;@m32
> Selected multilib: .;@m64
>
> Konstantin
>
> > return 0;
> >
> > struct iphdr *iphdr = (void *)(ether_header + 1);
> > if (iphdr->protocol != 17 || (iphdr->frag_off & 0x1ffff) != 0 ||
> > - iphdr->daddr != __builtin_bswap32(0x1020304))
> > + iphdr->daddr != htonl(0x1020304))
> > return 0;
> >
> > int hlen = iphdr->ihl * 4;
> > struct udphdr *udphdr = (void *)iphdr + hlen;
> >
> > - if (udphdr->dest != __builtin_bswap16(5000))
> > + if (udphdr->dest != htons(5000))
> > return 0;
> >
> > return 1;
> > diff --git a/test/bpf/t3.c b/test/bpf/t3.c index
> > 531b9cb8c..24298b7c7
> > 100644
> > --- a/test/bpf/t3.c
> > +++ b/test/bpf/t3.c
> > @@ -17,6 +17,7 @@
> > #include <net/ethernet.h>
> > #include <rte_config.h>
> > #include "mbuf.h"
> > +#include <arpa/inet.h>
> >
> > extern void rte_pktmbuf_dump(FILE *, const struct rte_mbuf *,
> > unsigned int);
> >
> > @@ -29,7 +30,7 @@ entry(const void *pkt)
> > mb = pkt;
> > eth = rte_pktmbuf_mtod(mb, const struct ether_header *);
> >
> > - if (eth->ether_type == __builtin_bswap16(ETHERTYPE_ARP))
> > + if (eth->ether_type == htons(ETHERTYPE_ARP))
> > rte_pktmbuf_dump(stdout, mb, 64);
> >
> > return 1;
> > --
> > 2.17.1
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