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Re: [PATCH] target/hppa: Allow, but diagnose, LDCW aligned only mod 4

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH] target/hppa: Allow, but diagnose, LDCW aligned only mod 4
Date: Sat, 18 Jan 2020 07:10:34 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2

On 1/17/20 8:23 PM, Richard Henderson wrote:
On 1/17/20 8:50 AM, Philippe Mathieu-Daudé wrote:
On Fri, Jan 17, 2020 at 2:53 AM Richard Henderson
<address@hidden> wrote:

The PA-RISC 1.1 specification says that LDCW must be aligned mod 16
or the operation is undefined.  However, real hardware only generates
an unaligned access trap for unaligned mod 4.

This Linux kernel commit seems relevant:


   /* From: "Jim Hull" <jim.hull of hp.com>
   I've attached a summary of the change, but basically, for PA 2.0, as
   long as the ",CO" (coherent operation) completer is specified, then the
   16-byte alignment requirement for ldcw and ldcd is relaxed, and instead
   they only require "natural" alignment (4-byte for ldcw, 8-byte for
   ldcd). */

It isn't completely relevant.  We don't implement hppa 2.0.

Oh... It was late and I misread it as:

  if (PA2)
    ... "instead of PA 2.0 ... the 16-byte alignment ... is
    relaxed, and insted only require "natural" alignment ..."


I added a TODO comment for HPPA64, as I said in reply to Dave Anglin elsewhere
in this thread.

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