Re: [PATCH 1/2] meson: define qemu_isa_flags

[Michael Tokarev]

07.10.2024 17:46, Richard Henderson пишет:
> On 10/7/24 01:43, Paolo Bonzini wrote:
> > Create a separate variable for compiler flags that enable
> > specific instruction set extensions, so that they can be used with
> > cc.compiles/cc.links.
> >
> > Note that -mfpmath=sse is a code generation option but it does not
> > enable new instructions, therefore I did not make it part of
> > qemu_isa_flags.
> >
> > Suggested-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> > Cc: qemu-stable@nongnu.org
> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > ---
> >   meson.build | 24 +++++++++++++++---------
> >   1 file changed, 15 insertions(+), 9 deletions(-)
> >
> > diff --git a/meson.build b/meson.build
> > index 76335bb2a51..bbb0f6d9bcf 100644
> > --- a/meson.build
> > +++ b/meson.build
> > @@ -335,6 +335,10 @@ elif host_os == 'windows'
> >     endif
> >   endif
> > +# Choose instruction set (currently x86-only)
> > +
> > +qemu_isa_flags = []
> > +
> >   # __sync_fetch_and_and requires at least -march=i486. Many toolchains
> >   # use i686 as default anyway, but for those that don't, an explicit
> >   # specification is necessary
> > @@ -351,7 +355,7 @@ if host_arch == 'i386' and not cc.links('''
> >       sfaa(&val);
> >       return val;
> >     }''')
> > -  qemu_common_flags = ['-march=i486'] + qemu_common_flags
> > +  qemu_isa_flags = ['-march=i486']
>
> Use += ?

Yes, it is better to use += here - when reviewing the patch this is
obvious qemu_isa_flags is empty at this point, but it wont be as
obvious in the actual code when initial assignment is quite far away
from this prepending.


> > -      qemu_common_flags = ['-mcx16'] + qemu_common_flags
> > +      qemu_isa_flags = ['-mcx16'] + qemu_isa_flags
>
> Likewise, why verbosely prepend, rather than append with += ?
> The same for all others, including
>
> > +qemu_common_flags = qemu_isa_flags + qemu_common_flags

I'd keep prepending here (but not in qemu_isa_flags above) because this
way it is possible to override some flags by the user.

/mjt