[dpdk-dev] [PATCH] net/tap: fix build issue with ARM32

[Ophir Munk]

> -----Original Message-----
> From: Jerin Jacob [mailto:jerin.jacob at caviumnetworks.com]
> Sent: Wednesday, January 31, 2018 1:31 PM
> To: Ophir Munk <ophirmu at mellanox.com>
> Cc: dev at dpdk.org; Thomas Monjalon <thomas at monjalon.net>; Pascal
> Mazon <pascal.mazon at 6wind.com>; Jan Viktorin
> <viktorin at rehivetech.com>; Jianbo Liu <jianbo.liu at arm.com>
> Subject: Re: [dpdk-dev] [PATCH] net/tap: fix build issue with ARM32
> 
> -----Original Message-----
> > Date: Wed, 31 Jan 2018 10:38:32 +0000
> > From: Ophir Munk <ophirmu at mellanox.com>
> > To: Jerin Jacob <jerin.jacob at caviumnetworks.com>
> > CC: "dev at dpdk.org" <dev at dpdk.org>, Thomas Monjalon
> > <thomas at monjalon.net>,  Pascal Mazon <pascal.mazon at 6wind.com>,
> Jan
> > Viktorin  <viktorin at rehivetech.com>, Jianbo Liu <jianbo.liu at arm.com>
> > Subject: RE: [dpdk-dev]  [PATCH] net/tap: fix build issue with ARM32
> >
> > Hi,
> > Please see inline
> >
> > > -----Original Message-----
> > > From: Jerin Jacob [mailto:jerin.jacob at caviumnetworks.com]
> > > Sent: Wednesday, January 31, 2018 12:24 PM
> > > To: Ophir Munk <ophirmu at mellanox.com>
> > > Cc: dev at dpdk.org; Thomas Monjalon <thomas at monjalon.net>; Pascal
> > > Mazon <pascal.mazon at 6wind.com>; Jan Viktorin
> > > <viktorin at rehivetech.com>; Jianbo Liu <jianbo.liu at arm.com>
> > > Subject: Re: [dpdk-dev] [PATCH] net/tap: fix build issue with ARM32
> > >
> > > -----Original Message-----
> > > > Date: Wed, 31 Jan 2018 09:59:45 +0000
> > > > From: Ophir Munk <ophirmu at mellanox.com>
> > > > To: Jerin Jacob <jerin.jacob at caviumnetworks.com>, "dev at dpdk.org"
> > > >  <dev at dpdk.org>
> > > > CC: Thomas Monjalon <thomas at monjalon.net>, Pascal Mazon
> > > > <pascal.mazon at 6wind.com>, Jan Viktorin <viktorin at rehivetech.com>,
> > > > Jianbo  Liu <jianbo.liu at arm.com>
> > > > Subject: RE: [dpdk-dev]  [PATCH] net/tap: fix build issue with
> > > > ARM32
> > > >
> > > > Hi,
> > > > Please see comments inline
> > > >
> > > > > -----Original Message-----
> > > > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Jerin Jacob
> > > > > Sent: Wednesday, January 31, 2018 7:14 AM
> > > > > To: dev at dpdk.org
> > > > > Cc: Thomas Monjalon <thomas at monjalon.net>; Jerin Jacob
> > > > > <jerin.jacob at caviumnetworks.com>; Pascal Mazon
> > > > > <pascal.mazon at 6wind.com>; Jan Viktorin
> > > > > <viktorin at rehivetech.com>; Jianbo Liu <jianbo.liu at arm.com>
> > > > > Subject: [dpdk-dev] [PATCH] net/tap: fix build issue with ARM32
> > > > >
> > > > > arm32 Linux does not support eBPF interface.
> > > > > Since tap PMD driver has a dependency on eBPF(the symbol
> > > > > __NR_bpf), disabling it armv7 config.
> > > > >
> > > > > compilation error log:
> > > > > In file included from /tmp/dpdk/drivers/net/tap/tap_bpf_api.c:15:0:
> > > > > /tmp/dpdk/drivers/net/tap/tap_bpf.h:103:4: error: #error
> > > > > __NR_bpf not defined  #  error __NR_bpf not defined
> > > > >     ^
> > > >
> > > > arm architecture is missing is file drivers/tap/tap_bpf.h I
> > > > suggest adding it, for example
> > > >
> > > > # elif defined(__arm__)
> > > > #  define __NR_bpf 386
> > >
> > > By looking at Linux source code
> > >
> https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fel
> > > ixi
> > > r.free-
> > >
> electrons.com%2Flinux%2Fv4.15%2Fsource%2Ftools%2Fbuild%2Ffeature%2
> > > Ftest-
> > >
> bpf.c%23L6&data=02%7C01%7Cophirmu%40mellanox.com%7C19f50ad7f27
> > >
> 34d00173808d56894c997%7Ca652971c7d2e4d9ba6a4d149256f461b%7C0%
> > >
> 7C0%7C636529910613736017&sdata=ynsxHG9fvao4LyfWLo4GVJjlKNmcF0q
> > > 0BkFocJyarAE%3D&reserved=0
> > > I am not sure, Is eBPF support available for arm32 support?
> >
> > TAP eBPF has a graceful approach: it must successfully compile on all
> > Linux distributions. If a specific kernel cannot support eBPF it will
> > gracefully refuse the eBPF netlink message sent to it.
> > Thus, there is no harm even if there is no eBPF support available for arm32.
> 
> OK. But, To enable grace full refuse, we should not any random system call
> number like #define __NR_bpf 386.
> It should at least unused for arm32.
> 

For arm - system call 386 seems to be used only for eBPF
http://elixir.free-electrons.com/linux/v4.15/source/arch/arm64/include/asm/unistd32.h#L796


> >
> > You should enable TAP compilation for cases where you only need TAP
> without eBPF.
> 
> Yes. It would have been better if new eBPF depended features would have
> under conditional compilation flag so it it can be turned off selectively.
> 

I am in favor of keeping configuration as simple as possible if possible.
I will issue a PR which includes arm BPF definition

> >
> > >
> > > >
> > > > It should work for you. Can you please try it?
> > >
> > > I don't have access to an arm32 board. I was facing cross
> > > compilation build issue with arm32.
> > >
> > > > If it doesn't work for you, please have a look in this link:
> > > >
> > > >
> > >
> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fs
> > > ou
> > > >
> > >
> rceforge.net%2Fp%2Fpredef%2Fwiki%2FArchitectures%2F&data=02%7C01%
> > > 7Coph
> > > >
> > >
> irmu%40mellanox.com%7C19f50ad7f2734d00173808d56894c997%7Ca6529
> > > 71c7d2e4
> > > >
> > >
> d9ba6a4d149256f461b%7C0%7C0%7C636529910613736017&sdata=g5fEkG
> > > Gwm%2BJgR
> > > > KyDrxJgbFII0%2B1%2BxtbT%2FE4Qy1HACEg%3D&reserved=0
> > > > where you can see more arm architecture definitions.
> > > > You should find the one suitable for you.
> > >
> > > I guess, it is not just matter of enabling the build for arm32. It
> > > should work at runtime too, If some can confirm following addition
> > > in the drivers/net/tap/tap_bpf.h works then we can add it.
> > >
> >
> > As mentioned above it must not work at runtime too.
> >
> > > # elif defined(__arm__)
> > > #  define __NR_bpf 386
> > >
> > > >
> > > > > /tmp/dpdk/drivers/net/tap/tap_bpf_api.c: In function ‘sys_bpf’:
> > > > > /tmp/dpdk/drivers/net/tap/tap_bpf_api.c:92:17: error: ‘__NR_bpf’
> > > > > undeclared (first use in this function)
> > > > >   return syscall(__NR_bpf, cmd, attr, size);
> > > > >                  ^
> > > > > /tmp/dpdk/drivers/net/tap/tap_bpf_api.c:92:17: note: each
> > > > > undeclared identifier is reported only once for each function it
> > > > > appears in
> > > > > /tmp/dpdk/drivers/net/tap/tap_bpf_api.c:93:1: error: control
> > > > > reaches end of non-void function [-Werror=return-type]  }  ^
> > > > > cc1: all warnings being treated as errors
> > > > >
> > > > > Fixes: b02d85e1 ("net/tap: add eBPF API")
> > > > >
> > > > > Cc: Pascal Mazon <pascal.mazon at 6wind.com>
> > > > > Cc: Jan Viktorin <viktorin at rehivetech.com>
> > > > > Cc: Jianbo Liu <jianbo.liu at arm.com>
> > > > >
> > > > > Signed-off-by: Jerin Jacob <jerin.jacob at caviumnetworks.com>
> > > > > ---
> > > > >  config/defconfig_arm-armv7a-linuxapp-gcc | 1 +
> > > > >  1 file changed, 1 insertion(+)
> > > > >
> > > > > diff --git a/config/defconfig_arm-armv7a-linuxapp-gcc
> > > > > b/config/defconfig_arm-armv7a-linuxapp-gcc
> > > > > index a20b7a85f..4a55bb397 100644
> > > > > --- a/config/defconfig_arm-armv7a-linuxapp-gcc
> > > > > +++ b/config/defconfig_arm-armv7a-linuxapp-gcc
> > > > > @@ -80,3 +80,4 @@ CONFIG_RTE_LIBRTE_BNX2X_PMD=n
> > > > > CONFIG_RTE_LIBRTE_QEDE_PMD=n
> > > CONFIG_RTE_LIBRTE_SFC_EFX_PMD=n
> > > > > CONFIG_RTE_LIBRTE_AVP_PMD=n
> > > > > +CONFIG_RTE_LIBRTE_PMD_TAP=n
> > > > > --
> > > >
> > > > I suggest fixing the compilation issue by adding the missing
> > > > architecture system call number (as suggested above) instead of
> > > > disabling TAP compilation by default
> > > >
> > > > > 2.16.1
> > > >