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

[Maciej W. Rozycki]

On Fri, 9 Nov 2018, Maciej W. Rozycki wrote:

> > 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
> 
>  Hmm, that's weird -- what executable did you check?  There may be some 
> that are n64, or maybe they've switched (which I would applaud, FWIW).  I 
> remember seeing mostly n32, with minimal support for n64, but that was a 
> while ago -- jessie or suchlike, I believe.  Using MIPS64r2 as the base 
> ISA also looks new to me, that used to be plain MIPS III, and some of 
> Debian's MIPS build systems used to be either MIPS III (Lemote Loongson) 
> or MIPS64r1 (Broadcom SiByte).

 OK, I definitely got this confused.  I did some checking and jessie 
didn't even have a 64-bit MIPS port.  I got their build systems right 
though, and the kernel is 64-bit for systems that support it.

> > Any binaries that need qemu-mipsn32 or qemu-mipsn32el?
> 
>  I'd expect at least the n32 dynamic loader (along with libc and some 
> other essential DSOs) to be present with MIPS64 Debian.  Traditionally, 
> under the FHS rules, it would be installed as /lib32/ld.so.1 (with the o32 
> one as /lib/ld.so.1 and the n64 as /lib64/ld.so.1), but Debian uses their 
> own multiarch filesystem layout standard, and offhand I don't remember 
> what the paths are defined to there.

 So with jessie you can install the `libc6-dev-mipsn32' package, which 
will get you n32 glibc development libraries and will pull the 
complementing n32 dynamic loader (at /lib32/ld.so.1 actually) and n32 
glibc shared libraries as well.

 Unfortunately multilib support files, such as the CRT files, seem to be 
missing from GCC for n32 or I cannot find them.  Otherwise you would be 
able to compile and link n32 binaries just by calling `gcc -mabi=n32'.  
Still the dynamic loader is directly runnable, as I noted above.

 HTH,

  Maciej