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Date:	Mon, 4 Feb 2019 15:27:37 +0100
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: 32 bit vs 64 bit Cygwin, followup
Message-ID:	<20190204142737.GO3532@calimero.vinschen.de>
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On Feb  4 09:16, Sam Habiel wrote:
> >That's not GCC fault.  You're running varargs, written for the standard
> >stack layout of the MSABI target from a function with a stack laid out
> >in SYSV ABI.  That can't work.
>=20
> I did some research to see how to write my own version of varargs (the
> code base is already instrumented to do different versions of varargs
> based on operating system). What I noticed though is that after
> disassembling code for win64 abi vs sysv abi, it seems like gcc/crt is
> attempting to do the right thing. There is different code for sysv vs
> win64 for va_start.
>=20
> sysv:
> 10        va_list vl;
> 11        va_start(vl,n);
>    0x00000001004010e4 <+100>:   movl   $0x8,-0xc8(%rbp)
>    0x00000001004010ee <+110>:   movl   $0x30,-0xc4(%rbp)
>    0x00000001004010f8 <+120>:   lea    0x10(%rbp),%rax
>    0x00000001004010fc <+124>:   mov    %rax,-0xc0(%rbp)
>    0x0000000100401103 <+131>:   lea    -0xb0(%rbp),%rax
>    0x000000010040110a <+138>:   mov    %rax,-0xb8(%rbp)
>=20
> win64:
> 10        va_list vl;
> 11        va_start(vl,n);
>    0x00000001004010a3 <+35>:    lea    0x18(%rbp),%rax
>    0x00000001004010a7 <+39>:    mov    %rax,-0x18(%rbp)
>=20
> So there may be a incomplete support for varargs for the sysv abi--but bu=
ggy.
>=20
> I attached the disassembly as well as the testing programs for your conve=
nience.

There's nothing for me to do here.  You still have to make sure
to choose the right varargs version and if there's really a bug,
you really should report it to GCC.


Corinna

--=20
Corinna Vinschen
Cygwin Maintainer

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