Re: [edk2-devel] [PATCH] RedfishPkg/JsonLib: Fix build errors

["Abner Chang" <abner.chang@hpe.com>]

> -----Original Message-----
> From: Chang, Abner (HPS SW/FW Technologist)
> Sent: Thursday, January 28, 2021 10:31 PM
> To: Leif Lindholm <leif@nuviainc.com>
> Cc: devel@edk2.groups.io; Wang, Nickle (HPS SW) <nickle.wang@hpe.com>;
> Michael D Kinney <michael.d.kinney@intel.com>
> Subject: RE: [edk2-devel] [PATCH] RedfishPkg/JsonLib: Fix build errors
> 
> 
> 
> > -----Original Message-----
> > From: Leif Lindholm [mailto:leif@nuviainc.com]
> > Sent: Thursday, January 28, 2021 7:17 PM
> > To: Chang, Abner (HPS SW/FW Technologist) <abner.chang@hpe.com>
> > Cc: devel@edk2.groups.io; Wang, Nickle (HPS SW)
> <nickle.wang@hpe.com>;
> > Michael D Kinney <michael.d.kinney@intel.com>
> > Subject: Re: [edk2-devel] [PATCH] RedfishPkg/JsonLib: Fix build errors
> >
> > On Thu, Jan 28, 2021 at 04:02:54 +0000, Chang, Abner (HPS SW/FW
> > Technologist) wrote:
> > > > > +  #   C4706: assignment within conditional expression
> > > > >    #
> > > > >    # Define macro HAVE_CONFIG_H to include
> > > > > jansson_private_config.h to
> > > > build.
> > > > >    # Undefined _WIN32, WIN64, _MSC_VER macros
> > > > >    # On GCC, no error on the unused-function and unused-but-set-
> > variable.
> > > > >    #
> > > > > -  MSFT:*_*_X64_CC_FLAGS = /wd4204 /wd4244 /wd4090 /wd4334
> > > > > /DHAVE_CONFIG_H=1 /U_WIN32 /UWIN64 /U_MSC_VER
> > > > > -  MSFT:*_*_IA32_CC_FLAGS = /wd4204 /wd4244 /wd4090
> > > > /DHAVE_CONFIG_H=1
> > > > > /U_WIN32 /UWIN64 /U_MSC_VER
> > > > > +  MSFT:*_*_X64_CC_FLAGS = /wd4204 /wd4244 /wd4090 /wd4334
> > > > /wd4706
> > > > > + /DHAVE_CONFIG_H=1 /U_WIN32 /UWIN64 /U_MSC_VER
> > > > > + MSFT:*_*_IA32_CC_FLAGS = /wd4204 /wd4244 /wd4090 /wd4706
> > > > > + /DHAVE_CONFIG_H=1 /U_WIN32 /UWIN64 /U_MSC_VER
> > > >
> > > > Urgh, please don't do this.
> > > > C4706 is what gives you a warning for accidentally assigning
> > > > instead of comparing. It's our last defence against the
> > > > jeopardy-comparing hordes that think
> > > >   if (NULL == Ptr)
> > > > is a sensible way of writing C.
> > > >
> > > > What is the actual problem being encountered?
> > >
> > > That is because we use the macro defined in open source header file,
> > > RedfishPkg/Library/JsonLib/jansson/src/jansson.h
> > >
> > > #define json_object_foreach(object, key, value)                                          \
> > >     for (key = json_object_iter_key(json_object_iter(object));
> \
> > >          key && (value =
> > json_object_iter_value(json_object_key_to_iter(key)));          \
> > >          key = json_object_iter_key(                                                     \
> > >              json_object_iter_next(object,
> > > json_object_key_to_iter(key))))
> >
> > Yay, "optimisation" by using preprocessor...
> >
> > Apart from how this ought to be a helper function:
> > - No parentheses around parameters in macro.
> > - Setting "value" at each iteration through the loop condition.
> > - Slinging parentheses like it's a lisp convention.
> >   - And it would be worse if they treated the parameters properly.
> >
> > If we ignore the other issues, the below should be functionally
> > equivalent and build on VS without disabling the warning:
> >
> >   for (key = json_object_iter_key(json_object_iter(object));                           \
> >        key;                                                                            \
> >        key = json_object_iter_key(                                                     \
> >             json_object_iter_next(object, json_object_key_to_iter(key))))
> > {            \
> >     value = json_object_iter_value(json_object_key_to_iter(key));
> > \
> >     if (!value)                                                                        \
> >       break;                                                                           \
> >   }
> >
> > Could you try to convince upstream to take the patch?
> Sure, I just sent an email to community, hope we can get the feedback soon.
> 
> Leif, that may takes time to have this patch to be in upstream (if they agree
> with it)... I have another PR which is not get merged yet.
> This will block our works on edk2, thus I would like to just add build option to
> suppress this build error. The build option is only for JsonLib though. Do you
> agree with this?
I am working on the PR of your patch for jannson community, however I realize that the patch doesn't work well with the jansson lib. The purpose of this macro is to define the for-loop statement, but the "break" in the code body breaks the usage of these macros. Below is one of the use cases of macro "json_object_foreach" which is used as the for-loop statement and simple to use for users to write the code block,

In value.c,
    json_object_foreach(other, key, value) {
        json_t *v = json_object_get(object, key);

        if (json_is_object(v) && json_is_object(value)) {
            if (do_object_update_recursive(v, value, parents)) {
                res = -1;
                break;
            }
        } else {
            if (json_object_set_nocheck(object, key, value)) {
                res = -1;
                break;
            }
        }
    }

I would just keep these macros and the source code which uses these macros unchanged. Use the build option to ignore the warning message on VS for the open source jansson lib.

Regards,
Abner
> 
> Thanks
> Abner
> 
> >
> > > > Beyond that, this will probably be an issue for all architectures,
> > > > so why add explicit (identical) workarounds for IA32/X64?
> > >
> > > I didn't catch this build error on GCC. You may know why?
> >
> > Ugh.
> > This is because (for whatever reason), both clang and GCC suppress
> > this warning if you add parentheses around the assignment. VS does not.
> >
> > /
> >     Leif