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Date: Fri, 9 Nov 2018 14:14:10 +0000 (GMT)
Sender: "Maciej W. Rozycki" <macro@linux-mips.org>
From: "Maciej W. Rozycki" <macro@linux-mips.org>
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Subject: Re: [Qemu-devel] [PATCH 0/2] linux-user/mips: Support the n32 ABI
 for the R5900
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To: Laurent Vivier <laurent@vivier.eu>
Cc: Fredrik Noring <noring@nocrew.org>, Aleksandar Markovic <amarkovic@wavecomp.com>, Aurelien Jarno <aurelien@aurel32.net>, =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= <f4bug@amsat.org>, =?UTF-8?Q?J=C3=BCrgen_Urban?= <JuergenUrban@gmx.de>, qemu-devel@nongnu.org

On Fri, 9 Nov 2018, Laurent Vivier wrote:

> if you have time, o32 & n32 support needs to be reworked.
> 
> We have two binaries qemu-mips and qemu-mipsn32 sharing the same ELF
> mask/magic.
> 
> As n32 identifies a kernel ABI version, we should have only one binary
> for qemu-mips and qemu-mipsn32 and the ABI version should be identified
> at runtime as it is done for ARM:
> 
>   ce4defa062 Arm Linux EABI syscall support.

 Are you sure?  So is the ARM ABI handled with ce4defa062 64-bit?

 The o32 ABI is 32-bit (32-bit GPR width) while n32 is 64-bit (64-bit GPR 
width).  The correspondence between the i386 ABI and the x86-64 x32 ABI is 
analogous to these two ABIs.

 How are these x86 ABIs handled WRT the user emulation mode; are they 
analogous to the ARM ABIs you've mentioned?

> [I think we can use e_flags for that]

 The EF_MIPS_ABI2 `e_flags' bit denotes the n32 ABI.  The container format 
is ELF32 obviously, because addressing is 32-bit with n32.

> I never did the change because I don't know where to find mipsn32
> binaries to test my changes.

 I believe MIPS64 Debian is all n32.

  Maciej