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

[YunQiang Su]

在 2020-02-26三的 17:45 +0800，Shiyou Yin写道：
> > -----Original Message-----
> > From: YunQiang Su [mailto:wzssyqa at gmail.com]
> > Sent: Saturday, February 22, 2020 10:20 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.
> > 
> 
> If this is what you mean, I will agree and update the patch.
> It should be noted that we still need to manually specify appropriate
> option to enable MMI correctly.
> The only change is now we have two new ways(2 & 3) to specify this
> option:
> 1) LS_CFLAGS
> 2) CC
> 3)compiler's default cflags, such as COLLECT_GCC_OPTIONS of gcc.
> 
> 
> Diff is as follows:
> 
> diff --git a/configure.ac b/configure.ac
> index 1ca3974..be9212d 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -78,7 +78,7 @@ AC_C_BIGENDIAN
>  AC_C_INLINE
>  
>  dnl PIXMAN_LINK_WITH_ENV(env-setup, program, true-action, false-
> action)
> -dnl
> +
>  dnl Compiles and links the given program in the environment setup by
> env-setup
>  dnl and executes true-action on success and false-action on failure.
>  AC_DEFUN([PIXMAN_LINK_WITH_ENV],[dnl
> @@ -273,7 +273,27 @@ dnl
> =====================================================================
> ======
>  dnl Check for Loongson Multimedia Instructions
>  
>  if test "x$LS_CFLAGS" = "x" ; then
> -    LS_CFLAGS="-march=loongson2f"
> +  # check default cflags to set LS_CFLAGS
> +  # Has -mloongson-mmi or -march=loongson3a : LS_CFLAGS="-mloongson-
> mmi"
> +  # else : LS_CFLAGS="-march=loongson2f"
> +  xserver_save_CFLAGS=$CFLAGS
> +  CFLAGS=" $LS_CFLAGS $CFLAGS -I$srcdir"
> +AC_RUN_IFELSE([AC_LANG_SOURCE([[
> +int main () {
> +  /* check default cflags */
> +  #ifndef __mips_loongson_mmi
> +  /* No -mloongson-mmi,-march=loongson3a and -march=loongson2f */
> +  return 0;
> +  #else
> +    #ifdef _MIPS_ARCH_LOONGSON2F
> +    /* Has -march=loongson2f */
> +    return 0;
> +    #else
> +    /* Has -mloongson-mmi or -march=loongson3a */
> +    return 1;
> +    #endif
> +  #endif
> +}]])], LS_CFLAGS="-mloongson-mmi", LS_CFLAGS="-march=loongson2f")

I am sorry. The setting to Loongson2f by default is not done by you.
It is my mistake.

Anyway, since you are working on that patch:

In the first patch, you setting 3A/MMI default instead of 2F. If that
patch was merged, Debian/OpenWrt etc will be broken just now.
In fact in most case the set 2F, it will not broken Debian, since the
the next link test will fail: 2F cannot interlink with
mips64r2/mips32r2. aka LS_CFLAGS is set to 2F will only break
mips3/mips2 OS.
Set LS_CFLAGS to -mloongson-mmi will break almost *ALL* os.
Is it your mistake?

In the second patch: you read CPU info from /proc/cpuinfo: WTF

I asked that you should keep loongson options not set by default
serveral times.
In your *3rd* patch, you still keep them set by default.

I told you that you can determine OS/CC behivors by predefined macros,
You still cannot understand after I have a loooooong talk with you by
wechat! WTF.

Almost (if not all) of Loongson guys are *RUBBISH*.
Let me sign this mail by my PGP key.

>  fi
>  
>  have_loongson_mmi=no
> 
> 
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