Re: [Qemu-devel] [PATCH 0/2] linux-user/mips: Support the n32 ABI for the R5900

[Laurent Vivier]

On 09/11/2018 15:14, Maciej W. Rozycki wrote:
> 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?

I'm sure of nothing. It's why it's better if someone involved in mips
development has an opinion on it :)

>  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.

OK, I understand better. It looks like qemu-sparc32plus or qemu-ppc64abi32.
If this is the case, you're right we need different binaries.

>> 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.

Some readelf results:

mips64el/stretch

  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
  Class:   ELF64
  Flags:   0x80000007, noreorder, pic, cpic, mips64r2

mipsel/stretch

  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
  Class:   ELF32
  Flags:   0x70001007, noreorder, pic, cpic, o32, mips32r2

mips/stretch/bin

  Magic:   7f 45 4c 46 01 02 01 00 00 00 00 00 00 00 00 00
  Class:   ELF32
  Flags:   0x70001007, noreorder, pic, cpic, o32, mips32r2

So 32bit mips are all o32, 64bit is n32.

Are there any distros that are 32bit but n32?
Any binaries that need qemu-mipsn32 or qemu-mipsn32el?

Thanks,
Laurent