Process map and fork problems

Corinna Vinschen
Wed Apr 20 10:50:00 GMT 2016

Hi Achim,

On Apr 20 10:27, Achim Gratz wrote:
> I'm chasing a problem on some 32bit Windows installs that supposedly
> happened after one of the Windows updates (and probably other software
> updates) in the last few months (the affected users were unable to pin it
> down further unfortunately).  It's obviously caused by two heap sections in
> the process map that are smack dab in the middle of the address range used
> by rebase:
> 20000000-200A0000 rw-p 00000000 0000:0000 0                   [heap]
> 200A0000-38000000 ===p 000A0000 0000:0000 0                   [heap]

This is one heap.  The first region is just the already committed
part, the remainder is the reserved part.

THis is the standard Cygwin heap area on 32 bit machines, which always
starts at 0x20000000.

> These do not exist on 32bit Cygwin installs on 64bit Windows installations,

On 64 bit systems, 32 bit applications have a 4 Gig virtual address
space.  On 32 bit systems, procecces only have a 2 Gig virtual address
space, unless the /3gb kernel option is given.

On 64 bit systems and on /3gb enabled 32 bit systems, the heap of 32 bit
Cygwin processes always starts at 0x80000000L.

Since that isn't available on 32 bit systems by default, the heap has
to start within the lower 2 Gigs.  That's where the 0x2000000 address
comes from.

If you have collisions because you're providing too many Cygwin DLLs,
you have to tweak these installations manually.


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