Re: [PATCH v2 1/4] scripts/tracetool: Fix dtrace generation for macOS

[Roman Bolshakov <r.bolshakov@yadro.com>]

On Sun, Jul 19, 2020 at 03:52:08PM +0200, Philippe Mathieu-Daudé wrote:
> On 7/17/20 11:35 AM, Roman Bolshakov wrote:
> > dtrace USDT is fully supported since OS X 10.6. There are a few
> > peculiarities compared to other dtrace flavors.
> > 
> > 1. It doesn't accept empty files.
> > 2. It doesn't recognize bool type but accepts C99 _Bool.
> > 3. It converts int8_t * in probe points to char * in
> >    header files and introduces [-Wpointer-sign] warning.
> > 
> > Cc: Cameron Esfahani <dirty@apple.com>
> > Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
> > ---
> >  scripts/tracetool/format/d.py | 15 ++++++++++++++-
> >  1 file changed, 14 insertions(+), 1 deletion(-)
> > 
> > diff --git a/scripts/tracetool/format/d.py b/scripts/tracetool/format/d.py
> > index 0afb5f3f47..353722f89c 100644
> > --- a/scripts/tracetool/format/d.py
> > +++ b/scripts/tracetool/format/d.py
> > @@ -13,6 +13,7 @@ __email__      = "stefanha@redhat.com"
> >  
> >  
> >  from tracetool import out
> > +from sys import platform
> >  
> >  
> >  # Reserved keywords from
> > @@ -34,7 +35,8 @@ def generate(events, backend, group):
> >  
> >      # SystemTap's dtrace(1) warns about empty "provider qemu {}" but is happy
> >      # with an empty file.  Avoid the warning.
> > -    if not events:
> > +    # But dtrace on macOS can't deal with empty files.
> > +    if not events and platform != "darwin":
> 
> or?

no, the event list is empty for some files where all events are
disabled (e.g. hppa/trace-events), so it should have an "and" here. This
limits early exit only on macOS. The precendence looks correct:

https://docs.python.org/3/reference/expressions.html#operator-precedence

> 
> >          return
> >  
> >      out('/* This file is autogenerated by tracetool, do not edit. */'
> > @@ -44,6 +46,17 @@ def generate(events, backend, group):
> >      for e in events:
> >          args = []
> >          for type_, name in e.args:
> > +            if platform == "darwin":
> > +                # macOS dtrace accepts only C99 _Bool
> 
> Why not do that for all platforms?
> 

Because I can only test the changes on darwin :)
I don't know how other dtrace flavors behave and whether it is an issue
for dtrace on Linux/Solaris/FreeBSD/etc.

Thanks,
Roman

> > +                if type_ == 'bool':
> > +                    type_ = '_Bool'
> > +                if type_ == 'bool *':
> > +                    type_ = '_Bool *'
> > +                # It converts int8_t * in probe points to char * in header
> > +                # files and introduces [-Wpointer-sign] warning.
> > +                # Avoid it by changing probe type to signed char * beforehand.
> > +                if type_ == 'int8_t *':
> > +                    type_ = 'signed char *'
> >              if name in RESERVED_WORDS:
> >                  name += '_'
> >              args.append(type_ + ' ' + name)
> > 
>