[Pixman] [PATCH v2 2/3] build: use '-mloongson-mmi' for Loongson MMI.

Sat Feb 22 14:20:15 UTC 2020

Shiyou Yin <yinshiyou-hf at loongson.cn> 于2020年2月22日周六 下午9:19写道：
>
> First let's clarify what exactly compatibility mean, or what specific goals we want to achieve.
>
> If it's just ensure the features of new code consistent with old compilation and hardware
> environment, then this patch will works well.
>

Of course that is not enough. If it is the only your goal, why sent this patch?

> If it is going to make sure MMI can be enabled and works well on each cases, it may be not easy.
>
> Guess compiler? Compiler check can only ensure the compile option is supported or not

yq at ls3b1500:~$ gcc -march=loongson3a -dM -E - < /dev/null | grep mmi
#define __mips_loongson_mmi 1

So, you can try to compile (-c) the bellow code to test whether the
compiler has MMI enabled

#ifndef __mips_loongson_mmi
# error "Loongson MMI is not supported"
#endif

For example, mipsel-linux-gnu-gcc is a generic mips compiler and
target mips32r2;
and the user set CC="mipsel-linux-gnu-gcc -march=loongson3",
Your test can still pass.

> and then MMI instruction can be compiled. We can't ensure the binary can works well on
> each hardware, especially in the case of cross-compilation.

Sure, that why you need to obey users configure, by LS_CFLAGS or CC or
the default configure of compiler.

> Almost all latest gcc support "-march=loongson2f" and "-march=loongson3a"
> and "-mloongson-mmi". So which kind of compiler we will set LS_CFLAGS as -mloongson-mmi?

due to history reason, the default value of LS_CFLAGS should be keep as 2f, and
user can set it by

LS_CFLAGS="-mloongson-mmi" ./configure -- blabla

>
> Guess CPU is always used in runtime check, it should be added in the optimization code but not in
> configure. The configure just need to ensure the compile process can finished successfully,
> So it may check compiler support some options or not and then enable/disable the features.
>

Generally, we don't need to guess the BUILD_MACHINE's cpu in buildtime.

>
> >-----Original Message-----
> >From: YunQiang Su [mailto:wzssyqa at gmail.com]
> >Sent: Friday, February 21, 2020 10:12 PM
> >To: Shiyou Yin
> >Cc: pixman at lists.freedesktop.org
> >Subject: Re: [Pixman] [PATCH v2 2/3] build: use '-mloongson-mmi' for Loongson MMI.
> >
> >Shiyou Yin <yinshiyou-hf at loongson.cn> 于2020年2月21日周五 下午9:47写道：
> >>
> >> >1. it breaks cross building
> >> This patch only let '-march=loongson2f' can be replaced with '-march=loongson-mmi'
> >> when compile locally on Loongson-3A. In other cases, nothing will be changed.
> >>
> >> >2. qemu-user mode cannot make /proc/cpuinfo correct
> >> >3. sometimes, some user may want to build software in a chroot env
> >> >without /proc bind mount.
> >> If there are no '/proc/cpuinfo', grep will return nonzero, -march=loongson2f will be
> >> setted just like what it was setted before.
> >>
> >> Thanks very much, Your analysis is very comprehensive,
> >> do you have a fix to satisfy all the above cases.
> >>
> >> This patch can let us compile locally on Loongson-3A without setting option 'LS_CFLAGS=***'.
> >> In other cases like what you said, specify 'LS_CFLAGS=***' while compile may be the best approach.
> >
> >The generic use case is like:
> >
> >if not-defined LS_CFLAGS;then
> >    reuslt=do_some_guess(compiler)
> >    if not result;then
> >        reuslt=do_some_guess(cpuinfo)
> >    fi
> >    if yes result;then
> >        use_3a()
> >    fi
> >else
> >    use_2f()
> >fi
> >
> >Since as I know, some of your internal toolchains are configured:
> >    --with-cpu=longson3a
> >If you don't determine compiler, you will override the default
> >configuration of gcc.
> >
> >>
> >> >-----Original Message-----
> >> >From: YunQiang Su [mailto:wzssyqa at gmail.com]
> >> >Sent: Thursday, February 20, 2020 10:30 PM
> >> >To: Yin Shiyou
> >> >Cc: pixman at lists.freedesktop.org
> >> >Subject: Re: [Pixman] [PATCH v2 2/3] build: use '-mloongson-mmi' for Loongson MMI.
> >> >
> >> >Yin Shiyou <yinshiyou-hf at loongson.cn> 于2020年2月20日周四 下午10:23写道：
> >> >>
> >> >> It's suggested to use '-mloongson-mmi' to enable MMI.
> >> >> To keep compatible with old processor, '-mloongson-mmi' will be
> >> >> setted for Loongson-3A only.
> >> >
> >> >Please resend the whole patch set.
> >> >
> >> >> ---
> >> >>  configure.ac | 8 ++++++--
> >> >>  meson.build  | 2 +-
> >> >>  2 files changed, 7 insertions(+), 3 deletions(-)
> >> >>
> >> >> diff --git a/configure.ac b/configure.ac
> >> >> index 1ca3974..2548799 100644
> >> >> --- a/configure.ac
> >> >> +++ b/configure.ac
> >> >> @@ -271,9 +271,13 @@ PIXMAN_CHECK_CFLAG([-xldscope=hidden], [dnl
> >> >>
> >> >>  dnl ===========================================================================
> >> >>  dnl Check for Loongson Multimedia Instructions
> >> >> -
> >> >>  if test "x$LS_CFLAGS" = "x" ; then
> >> >> -    LS_CFLAGS="-march=loongson2f"
> >> >> +    IS_LOONGSON_3A=`grep "Loongson-3A" /proc/cpuinfo`
> >> >
> >> >It is a bad way to determine CPU from cpuinfo:
> >> >
> >> >1. it breaks cross building
> >> >2. qemu-user mode cannot make /proc/cpuinfo correct
> >> >3. sometimes, some user may want to build software in a chroot env
> >> >without /proc bind mount.
> >> >
> >> >> +    if test $? -eq 0 -a -n "$IS_LOONGSON_3A" ; then
> >> >> +        LS_CFLAGS="-mloongson-mmi"
> >> >> +    else
> >> >> +        LS_CFLAGS="-march=loongson2f"
> >> >> +    fi
> >> >>  fi
> >> >>
> >> >>  have_loongson_mmi=no
> >> >> diff --git a/meson.build b/meson.build
> >> >> index 15d3409..a45c969 100644
> >> >> --- a/meson.build
> >> >> +++ b/meson.build
> >> >> @@ -51,7 +51,7 @@ endforeach
> >> >>
> >> >>  use_loongson_mmi = get_option('loongson-mmi')
> >> >>  have_loongson_mmi = false
> >> >> -loongson_mmi_flags = ['-march=loongson2f']
> >> >> +loongson_mmi_flags = ['-mloongson-mmi']
> >> >>  if not use_loongson_mmi.disabled()
> >> >>    if host_machine.cpu_family() == 'mips64' and cc.compiles('''
> >> >>        #ifndef __mips_loongson_vector_rev
> >> >> --
> >> >> 2.1.0
> >> >>
> >> >> _______________________________________________
> >> >> Pixman mailing list
> >> >> Pixman at lists.freedesktop.org
> >> >> https://lists.freedesktop.org/mailman/listinfo/pixman
> >> >
> >> >
> >> >
> >> >--
> >> >YunQiang Su
> >>
> >
> >
> >--
> >YunQiang Su
>

-- 
YunQiang Su