[Simh] O2 optimization on Linux (was: VMS 4.6 crashes on Linux)

[Peter Allan]

On 28 December 2010 22:00, Bob Supnik <bob at supnik.org> wrote:

> Jason Stevens wrote:
>
> You didn't build it with -O2 on linux did you?  There is some weird
> things with GCC and SIMH's VAX...  I can only speak to 4.X BSD, but I
> was able to identify two procedures that when optimized with -O2 break
> 4BSD on SIMH....
>
> I kind of detailed it here:
>
> http://www.mail-archive.com/simh@trailing-edge.com/msg00463.html
>
> And the procedures in question were:
>
> op_ldpctx
> op_mtpr
>
> ---
>
> Interestingly, those routines are the ONLY places in the VAX simulator
> where these macros are used:
>
> /* Machine specific reserved operand tests (all NOPs) */
>
> #define ML_PA_TEST(r)
> #define ML_LR_TEST(r)
> #define ML_SBR_TEST(r)
> #define ML_PXBR_TEST(r)
> #define LP_AST_TEST(r)
> #define LP_MBZ84_TEST(r)
> #define LP_MBZ92_TEST(r)
>
> On the 780, they are real tests:
>
> /* Machine specific reserved operand tests */
>
> #define ML_LR_TEST(r)    if ((uint32)((r)&  0xFFFFFF)>  0x200000)
> RSVD_OPND_FAULT
> #define ML_PXBR_TEST(r)  if ((((r)&  0x80000000) == 0) || \
>                            ((r)&  0x00000003)) RSVD_OPND_FAULT
> #define ML_SBR_TEST(r)   if ((r)&  0x00000003) RSVD_OPND_FAULT
> #define ML_PA_TEST(r)    if ((r)&  0x00000003) RSVD_OPND_FAULT
> #define LP_AST_TEST(r)   if ((r)>  AST_MAX) RSVD_OPND_FAULT
> #define LP_MBZ84_TEST(r) if ((r)&  0xF8C00000) RSVD_OPND_FAULT
> #define LP_MBZ92_TEST(r) if ((r)&  0x7FC00000) RSVD_OPND_FAULT
>
> ---
>
> One (or more) of those six tests is the smoking gun, and if I had to put my
> money on it, I think it's this one:
>
> #define ML_LR_TEST(r)    if ((uint32)((r)&  0xFFFFFF)>  0x200000)
> RSVD_OPND_FAULT
>
> Try adding an extra level of parentheses:
>
> if (((uint32)((r)&  0xFFFFFF))>  0x200000) RSVD_OPND_FAULT
>
>
> just to be sure that the uint32 cast isn't be applied to the whole
> comparison, instead of just the first term.
>
> If that fails to get it running, then try "no-oping" all of the macros to
> see if VMS 4.6 will boot.  If it does, then enable each of the macros in
> turn, to see where the simulator fails.
>
> /Bob
>
>
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>

Bob,

I tried removing the macro definitions one by one. The one that causes the
problem is ML_PXBR_TEST, i.e. if this is defined as nothing and the rest are
left as per vax780_defs.h, then the 780 emulator works on CentOS 5.5. This
is the macro with two comparisons in it. I wonder if that is significant?

I tried putting in some extra parentheses, but this did not help.

Of course, it all still works on Fedora Core 14. I will see if I can compare
the assembler that is generated for vax_cpu1.c on the two systems.

Peter Allan
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