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bug#12754: factor.c selects 64 bit code from longlong.h on 32-bit hppa s


From: John David Anglin
Subject: bug#12754: factor.c selects 64 bit code from longlong.h on 32-bit hppa systems
Date: Tue, 30 Oct 2012 11:40:56 -0400
User-agent: Mozilla/5.0 (Windows NT 5.1; rv:16.0) Gecko/20121010 Thunderbird/16.0.1

On 10/30/2012 5:57 AM, Torbjorn Granlund wrote:
The fix for this is long overdue and should be made to GCC; GCC should
not support generation of code that will cause register clobbering
issues.
As far as I'm aware, GCC does not generate code that will cause register clobbering
issues.  What applications do in asms is beyond the control of GCC.
GCC uses the 64-bit registers if PA 2.0 when it generates code for 2.0.
The parameter transfer is the same for the 2.0n and 1.0 ABIs.
Incorrect. GCC supports generate generation of PA 2.0 code for both 32 and 64-bit
environments.
The ABI=2.0w refers to a 64-bit HP-UX kernel.

Huh?
I assume you are thinking about the ABI parameter used by GMP.

Look at config.guess to see how it works. When it returns "hppa2.0w" for the target machine, the target has a 64-bit wide kernel and the compiler is generating code for the 32-bit runtime. It returns "hppa64" when the target is generating code for the 64-bit ELF runtime. In terms of assembly code, this is the difference between ".level 2.0" and
".level 2.0w".


   All 64-bit HP-UX kernels support both the 32 and 64-bit runtimes.  It
   is possible to optimize certain operations in the 32-bit runtime using
   the 64-bit registers on but the benefit is not as great as one might
   expect because of the calling convention requirements.

I expect a two-fold improvement for certain operations, and that's
indeed what we get in GMP.  But the speed issues seem secondary in this
discusson.  I regret the decison of the the Linux hppa hacker to not
support 2.0, but I respect it.  The correctness issues imposed by the
incomatibility of the kernel and GCC is much more serious.

You are essentially arguing for a second 32-bit runtime with 64-bit registers, calling conventions, probably based on ELF. I know there were discussions in HP about this
but it was never fully defined.

There is no incompatibility between GCC and the kernel as far as I know. Specifically,
what are you talking about?

The initial decisions regarding the runtime architecture for Linux were taken by HP and it contractors. Yes, it would have been nice if support was there for a full 64-bit context when the kernel was running on a PA 2.0 machine. Changing it now will
break userspace exception support in a variety of applications.

There are certainly some opportunities to improve optimizations for HP-UX specific code. In the present case, this can be tested for using the "__hpux__" preprocessor
define.

Dave

--
John David Anglin    address@hidden






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