* Guido van Rossum [2002-10-04 15:40 -0400]:

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Trying to get around to my mingw32 port again. I currently don't have Visual C++ installed, but why is this nonstandard _alloca needed? Can't it simply be replaced by alloca? Doesn't MSVC have alloca?

It seems that it does. But I guess _alloca is more politically correct, since alloca is not standard C.

I don't see how this applies, as neither form is standard C, but in practise, alloca is supported by all compilers I use, be it Windows or Linux. And I don't care about P. C. ;-)

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For the moment, I'm as far as building posixmodule.c, which I succeeded by doing a

#define _alloca alloca

If there's a way to kill MSVC peculiarities, could this please be done?

I'd be happy to do a global subst of _alloca -> alloca.

Mark, do you see any reason why this might *not* work?

Could it break other compilers?

No, as it's only used in platform-specific code as seen below: $ find . -name *.[ch]|xargs grep -w _alloca ./Modules/posixmodule.c: s1 = (char *)_alloca(i); ./Modules/posixmodule.c: s2 = (char *)_alloca(x); ./Modules/posixmodule.c: s2 = (char *)_alloca(x); ./Python/pythonrun.c: /* _alloca throws a stack overflow exception if there's ./Python/pythonrun.c: _alloca(PYOS_STACK_MARGIN * sizeof(void*)); $ find . -name *.[ch]|xargs grep -w alloca ./Modules/mpzmodule.c:** alloca with arg < 0 (when casted to a signed ./PC/_winreg.c:#include "malloc.h" /* for alloca */ ./PC/_winreg.c: retBuf = (char *)alloca(len); ./PC/_winreg.c: retValueBuf = (char *)alloca(retValueSize); ./PC/_winreg.c: retDataBuf = (char *)alloca(retDataSize); ./PC/_winreg.c: retBuf = (char *)alloca(bufSize); ./PC/_winreg.c: retBuf = (char *)alloca(bufSize); ./PC/import_nt.c:#include "malloc.h" /* for alloca */ ./PC/import_nt.c: /* alloca == no free required, but memory only local to fn, ./PC/import_nt.c: moduleKey = alloca(bufSize); ./PC/os2vacpp/getpathp.c:#include "malloc.h" // for alloca - see comments below! ./PC/os2vacpp/getpathp.c: // alloca == no free required, but memory only local to fn. ./PC/os2vacpp/getpathp.c: keyBuf = alloca(sizeof(keyPrefix)-1 + versionLen + sizeof(keySuffix)); // chars only, plus 1 NULL. So, alloca and _alloca are only used in platform specific Windows and OS/2 code. The MSVC specific code is a little inconsistent, it uses both _alloca and alloca forms depending on the source file.

A conservative approach would be to add #ifdef CYGWIN around the #define you propose.

Not even more #ifdefs, please. I'd suggest the global replace _alloca -> alloca. -- Gerhard

Guido van Rossum writes:

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Doesn't MSVC have alloca?

It seems that it does.

Without checking: It probably has this only if __STDC__ is not defined. MSVC hides all non-standard symbols if __STDC__ is defined - either by compiler switches, or in some application header. In that sense, _alloca is the Microsoft name for this extension. They may have been misguided by using that scheme, though, since _alloca isn't any more reserved than alloca. However, all uses of _alloca in posixmodule.c are MS specific, so I really see no reason to change that. Regards, Martin

* Christian Tismer [2002-10-04 18:16 -0700]:

Martin v. Loewis wrote:

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Guido van Rossum writes:

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Doesn't MSVC have alloca?

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It seems that it does.

Without checking: It probably has this only if __STDC__ is not defined. MSVC hides all non-standard symbols if __STDC__ is defined - either by compiler switches, or in some application header.

Hmm. I had this problem (no alloca, no idea why) and defined it by a macro in this case.

I've now installed MSVC6SP4 and verified that with my patch Python still builds ok. Obviously, Python's compiler options for MSVC don't define __STDC__.

Is it cleaner to undefine __STDC__ instead?

It'd be cleaner to use either _alloca or alloca, but not both like the current M$VC specific code does. -- Gerhard

...

Trying to get around to my mingw32 port again. I currently don't have Visual C++ installed, but why is this nonstandard _alloca needed? Can't it simply be replaced by alloca? Doesn't MSVC have alloca?

It seems that it does. But I guess _alloca is more politically correct, since alloca is not standard C.

...

For the moment, I'm as far as building posixmodule.c, which I succeeded by doing a

#define _alloca alloca

If there's a way to kill MSVC peculiarities, could this please be done?

I'd be happy to do a global subst of _alloca -> alloca.

Mark, do you see any reason why this might *not* work?

None at all. Mark.

As per suggestion of Guido, I've submitted a patch. The patch, however, doesn't make any sense standalone, so it's part of #1 of many mingw related patches.

So I should ignore the patch until you're done submitting those other patches?

These will ultimately make it possible to build Python on win32 using the autoconf/make toolchain.

I don't understand. How many Unix emulations on Windows do we need? We've already absorbed a sheer endless set of patches to make it work on CYGWIN. How does Mingw differ?

See http://python.org/sf/618791

I've assigned it to Guido for no good reason except being not sure if Mark knows about autoconf/makesetup, which my patch touches.

But I'd also be glad if anybody else applies it ;-)

Me too. I may reduce the priority. --Guido van Rossum (home page: http://www.python.org/~guido/)

On Fri, Oct 04, 2002 at 08:18:15PM -0400, Guido van Rossum wrote:

We've already absorbed a sheer endless set of patches to make it work on CYGWIN.

Ouch! :,) Nevertheless, the Cygwin community appreciates the continued support. Jason

[Guido]

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I'd be happy to do a global subst of _alloca -> alloca.

Mark, do you see any reason why this might *not* work?

[Mark]

None at all.

In the interest of universal harmony, I've done this and will check it in soon (when the tests complete). no-point-arguing-over-non-issues-ly y'rs - tim