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Date:	Fri, 14 Feb 2014 17:38:37 +0100
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: Interesting footnote about environment variables block
Message-ID:	<20140214163837.GH2246@calimero.vinschen.de>
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On Feb 14 16:22, Stephan Mueller wrote:
> Andrey Repin wrote:
>=20
> > http://www.microsoft.com/resources/documentation/windows/xp/all/proddoc=
s/en-us/ntcmds_shelloverview.mspx?pf=3Dtrue
> >=20
> >> The maximum total environment variable size for all variables, which
> >> includes variable names and the equal sign, is 65,536KB.
>=20
> The actual limit, on old OSes (such as Windows XP) is 64KB or 65536 bytes=
.  This text appears to contain a typo; likely someone decided to change fr=
om one representation to the other, and forgot to change the units when the=
y changed the number.  Newer OSes have lifted the 64KB limitation; I forget=
 exactly when.=20
>=20
> > http://msdn.microsoft.com/en-us/library/windows/desktop/ms682653(v=3Dvs=
.85).aspx
> > (And consequently,
> > http://msdn.microsoft.com/en-us/library/windows/desktop/ms682425(v=3Dvs=
.85).aspx
> > )
>=20
> These docs are the documentation for the CreateProcess API.  I'm guessing=
 the relevant text here is:
>=20
> 	The ANSI version of this function, CreateProcessA fails if the total siz=
e of the environment block for the process exceeds 32,767 characters.
>=20
> The limit described here is independent of the one in the XP documentatio=
n.  The typical behaviour of a large number of Windows FooA APIs is to wide=
n their argument strings from ANSI to UTF-16, and then call the FooW API to=
 do the actual work.  The 32K limit here is likely related to the size of t=
he buffer used for the temporary wide copy of the argument.
>=20
> > I don't know, how it is applicable to Cygwin.
>=20
> Likewise.=20

Cygwin is using fooW functions, so we should be on the safe side.
Except that a big Windows environment tends to move the usual
start addresses of the stack from the usual 0x30000 to something
else.  This can unfortunately break fork if the Windows environment
is >64K and the Windows environment changed in the forking process.


Corinna


--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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