Re: [PATCH 7/9] meson: make the CSPRNG backend configurable

> Patrick Steinhardt <ps@pks.im> writes:
> > +if csprng_backend in ['auto', 'arc4random'] and compiler.has_header_symbol('stdlib.h', 'arc4random_buf', required: csprng_backend == 'arc4random')
> >    libgit_c_args += '-DHAVE_ARC4RANDOM'
> > -elif compiler.has_header_symbol('bsd/stdlib.h', 'arc4random_buf')
> > +  csprng_backend = 'arc4random'
> > +elif csprng_backend in ['auto', 'arc4random_bsd'] and compiler.has_header_symbol('bsd/stdlib.h', 'arc4random_buf', required: csprng_backend == 'arc4random_bsd')
> >    libgit_c_args += '-DHAVE_ARC4RANDOM_BSD'
> > -elif compiler.has_function('getrandom', prefix: '#include <sys/random.h>')
> > +  csprng_backend = 'arc4random_bsd'
> > +elif csprng_backend in ['auto', 'getrandom'] and compiler.has_function('getrandom', prefix: '#include <sys/random.h>', required: csprng_backend == 'getrandom')
> >    libgit_c_args += '-DHAVE_GETRANDOM'
> > -elif compiler.has_function('getentropy', prefix: '#include <unistd.h>')
> > +  csprng_backend = 'getrandom'
> > +elif csprng_backend in ['auto', 'getentropy'] and compiler.has_function('getentropy', prefix: '#include <unistd.h>', required: csprng_backend == 'getentropy')
> >    libgit_c_args += '-DHAVE_GETENTROPY'
> > -elif compiler.has_function('RtlGenRandom', prefix: '#include <windows.h>\n#include <ntsecapi.h>')
> > +  csprng_backend = 'getentropy'
> > +elif csprng_backend in ['auto', 'rtlgenrandom'] and compiler.has_function('RtlGenRandom', prefix: '#include <windows.h>\n#include <ntsecapi.h>', required: csprng_backend == 'rtlgenrandom')
> >    libgit_c_args += '-DHAVE_RTLGENRANDOM'
> > -elif openssl.found()
> > +  csprng_backend = 'rtlgenrandom'
> > +elif csprng_backend in ['auto', 'openssl'] and openssl.found()
> >    libgit_c_args += '-DHAVE_OPENSSL_CSPRNG'
> > +  csprng_backend = 'openssl'
> > +elif csprng_backend in ['auto', 'urandom']
> > +  csprng_backend = 'urandom'
> > +else
> > +  error('Unsupported CSPRNG backend: ' + csprng_backend)
> >  endif
> 
> IIRC, the precedence order of CPP macros related to csprng backends
> were chosen to reflect our preference for more secure and faster
> ones over the ones that are less so.  Does the above list recreate
> the same order, and do we want to somehow make sure future
> developers would not break that order without knowing our intention,
> saying "when all things are equal, we should sort in alphabetical
> order" or something?