Re: Checking $host for 64-bit code generation

[Ralf Wildenhues]

* John Calcote wrote on Tue, Jun 24, 2008 at 05:51:05PM CEST:
> This bit of code is part of a larger chunk of code that fills in a
> Microsoft OS structure for walking the stack:
> 
> #ifdef FLM_64BIT
>   DWORD64 udDisplacement;
> #else
>   DWORD   udDisplacement;
> #endif

>   if (SymGetSymFromAddr(gv_hMemProcess,
>     *puiStack, &udDisplacement, pImgHlpSymbol))
>   ...
> 
> As you can see here, the OS function SymGetSymFromAddr expects to be
> passed a 64-bit quantity (DWORD64) on 64-bit platforms, and a 32-bit
> quantity (DWORD) on 32-bit platforms. Why didn't they define this
> parameter to use an opaque type, like size_t, for instance?

Well, even if they don't: unless you use SymGetSymFromAddr exactly once
(presumably in a wrapper function), why not do it yourself, and limit
the preprocessor magic to one spot:

  #ifdef FLM_64BIT
  typedef SymGetSymFromAddrDisp DWORD64;
  #else
  typedef SymGetSymFromAddrDisp DWORD;
  #endif

(/me shudders a bit about the naming convention) and use that
throughout?

> [...] you used the -m32/64
> flag as part of the compiler variable, not the flags variable. This
> would not have occurred to me, but it makes complete sense in hind
> sight. The -mxx flag changes the compiler in a very fundamental way, so
> it's best applied to the $CXX variable.

Well, I used to tell people to put it in CFLAGS/CXXFLAGS.  That's wrong
as then the preprocessor is neglected, should it run on its own anywhere
(it most likely will during some configure test).  So I started putting
it in both CPPFLAGS and LDFLAGS.  That's not so bad, in that it fixes
all interesting languages at once (except maybe un-preprocessed Fortran)
but it does require that these variables are not forgotten anywhere,
even in makefiles not written by automake.  Adding it to CC/CXX is
pretty safe.

Cheers,
Ralf