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Date: Mon, 14 Nov 2016 09:48:40 -0500
From: Neil Horman <nhorman@tuxdriver.com>
To: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Cc: Hemant Agrawal <hemant.agrawal@nxp.com>, "dev@dpdk.org" <dev@dpdk.org>,
 "users@dpdk.org" <users@dpdk.org>, "Jacob, Jerin" <Jerin.Jacob@cavium.com>,
 Jan Viktorin <viktorin@rehivetech.com>
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Subject: Re: [dpdk-dev] pmdinfogen issues: cross compilation for ARM fails
 with older host compiler
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On Mon, Nov 14, 2016 at 02:29:24AM +0530, Jerin Jacob wrote:
> On Fri, Nov 11, 2016 at 10:34:39AM +0000, Hemant Agrawal wrote:
> > Hi Neil,
> >                Pmdinfogen compiles with host compiler. It usages rte_byteorder.h of the target platform.
> > However, if the host compiler is older than 4.8, it will be an issue during cross compilation for some platforms.
> > e.g. if we are compiling on x86 host for ARM, x86 host compiler will not understand the arm asm instructions.
> > 
> > /* fix missing __builtin_bswap16 for gcc older then 4.8 */
> > #if !(__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 8))
> > static inline uint16_t rte_arch_bswap16(uint16_t _x)
> > {
> >                register uint16_t x = _x;
> >                asm volatile ("rev16 %0,%1"
> >                                     : "=r" (x)
> >                                     : "r" (x)
> >                                     );
> >                return x;
> > }
> > #endif
> > 
> > One easy solution is that we add compiler platform check in this code section of rte_byteorder.h
> > e.g
> > #if !(defined __arm__ || defined __aarch64__)
> > static inline uint16_t rte_arch_bswap16(uint16_t _x)
> > {
> >                return (_x >> 8) | ((_x << 8) & 0xff00);
> > }
> > #else ….
> > 
> > Is there a better way to fix it?
> 
> IMO, It is a HOST build infrastructure issue. If a host app is using the
> dpdk service then it should compile and link against HOST target(in this
> specific case, build/x86_64-native-linuxapp-gcc). I think, introducing the
> HOSTTARGET kind of scheme is a clean solution.
> 
> /Jerin
> 
> 
That would be accurate.  That is to say, pmdinfogen is a tool that should only
be run on the host doing the build, by the host doing the build, and so should
be compiled to run on the host, not on the target being built for.

Yeah, so what we need is a way to get to the host version of rte_byteorder.h
when building in a cross environment

Neil