On Nov 22 08:54, Jeremy Drake via Cygwin-patches wrote:
> On Fri, 22 Nov 2024, Corinna Vinschen wrote:
>
> > On Nov 21 11:42, Jeremy Drake via Cygwin-patches wrote:
> > > +#if defined (__x86_64__)
> > > + host_mach = IMAGE_FILE_MACHINE_AMD64;
> > > +#elif defined (__i386__)
> > > + host_mach = wow64 ? IMAGE_FILE_MACHINE_AMD64 :
> > > IMAGE_FILE_MACHINE_I386;
> > > +#else
> > > + /* this should not happen */
> >
> > It should actually result in
> >
> > #error unimplemented for this target
>
> No, because this is the fallback case for when IsWow64Process2 fails.
> This should only happen on OS versions that don't support it, which in
> turn don't support anything other than i386 and x86_64. However, OS
> versions that do support it also support ARM64. If/when Cygwin has native
> ARM64 support, this should not be a compilation error. If anything it may
> be a runtime error (assert?)
Aaaah, yeah, I see what you mean. In that case, just set host_mach to
IMAGE_FILE_MACHINE_AMD64 and be done with it. There's no other choice
in that case anyway.
> > > +extern const IMAGE_DOS_HEADER
> > > +dosheader __asm__ ("__image_base__");
> > > +
> > > +const USHORT
> > > +wincapc::current_module_machine () const
> > > +{
> > > + PIMAGE_NT_HEADERS ntheader = (PIMAGE_NT_HEADERS)((LPBYTE) &dosheader
> > > + + dosheader.e_lfanew);
> > > + return ntheader->FileHeader.Machine;
> > > }
> >
> > Just scratch that. First, we're using GetModuleHandle(NULL)
> > throughout to access the image base, but apart from that,
> > the info is already available in wincap via cpu_arch().
>
> GetModuleHandle(NULL) is the exe, __image_base__ is the cygwin dll.
> Theoretically, with ARM64EC, you can mix-and-match x86_64 and ARM64 in the
> same process,
Oh, ok, I read about this a while ago but had completely forgotten.
> so the most correct answer to the question to "are we being
> emulated" is whether the current module's architecture matches the host
> system's architecture.
>
> Yes, due to Windows already lying in Get(Native)SystemInfo, cpu_arch()
> will tell you this, but with *different* enums, which means you'll
> need a switch somewhere to translate between them, instead of just doing
> an == or != with the host like this function lets you do.
This OTOH is well known at compile time, so this is where an #ifdef
may be in order, i .e.
#if defined __x86_64__
current_mach = IMAGE_FILE_MACHINE_AMD64;
#else
#error unimplemented for this target
#endif
but, yeah, your code is simpler. I just don't like the name of the
function, wouldn't something like current_machine() or cygwin_machine()
be better?
Thanks,
Corinna
