Re: [PATCH] target/sparc: resolve ASI_USERTXT correctly

[M Bazz]

On Thu, Apr 11, 2024, 5:55 PM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 4/11/24 14:29, M Bazz wrote:
> > fixes a longstanding bug which causes a "Nonparity Synchronous Error"
> > kernel panic while using a debugger on Solaris / SunOS systems. The panic
> > would occur on the first attempt to single-step the process.
> >
> > The problem stems from an lda instruction on ASI_USERTXT (8). This asi
> > was not being resolved correctly by resolve_asi().
> >
> > Further details can be found in #2281
> >
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2281
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2059
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1609
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1166
> >
> > Signed-off-by: M Bazz <bazz@bazz1.com>
> > ---
> >   target/sparc/translate.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/target/sparc/translate.c b/target/sparc/translate.c
> > index 319934d9bd..1596005e22 100644
> > --- a/target/sparc/translate.c
> > +++ b/target/sparc/translate.c
> > @@ -3,6 +3,7 @@
> >
> >      Copyright (C) 2003 Thomas M. Ogrisegg <tom@fnord.at>
> >      Copyright (C) 2003-2005 Fabrice Bellard
> > +   Copyright (C) 2024 M Bazz <bazz@bazz1.com>
> >
> >      This library is free software; you can redistribute it and/or
> >      modify it under the terms of the GNU Lesser General Public
> > @@ -1159,6 +1160,7 @@ static DisasASI resolve_asi(DisasContext *dc, int 
> > asi, MemOp memop)
> >                  || (asi == ASI_USERDATA
> >                      && (dc->def->features & CPU_FEATURE_CASA))) {
> >           switch (asi) {
> > +        case ASI_USERTXT:    /* User text access */
> >           case ASI_USERDATA:   /* User data access */
> >               mem_idx = MMU_USER_IDX;
> >               type = GET_ASI_DIRECT;
>
> I don't believe this is correct, because it operates against the page's 
> "read" permissions
> instead of "execute" permissions.
>
>
> r~

Hi Richard,

Thanks for your guidance. It set me in the right direction. Now I
think I've got the right spot.

function `helper_ld_asi` has a block to help load ASI_KERNELTXT, but the
ASI_USERTXT case defaults to sparc_raise_mmu_fault(); I believe this
is the true culprit
source reference:
https://gitlab.com/qemu-project/qemu/-/blob/master/target/sparc/ldst_helper.c?ref_type=heads#L687

The code for the ASI_KERNELTXT seems generic enough to also use for
ASI_USERTXT verbatim.
See v2 patch below. I've done a `make test` -- all passing (3 skips).
OS boots, and the
debuggers are working without issue. What do you think?

Once we arrive at the right solution, I'll finalize the patch.
-bazz


diff --git a/target/sparc/ldst_helper.c b/target/sparc/ldst_helper.c
index e581bb42ac..4f87e44a93 100644
--- a/target/sparc/ldst_helper.c
+++ b/target/sparc/ldst_helper.c
@@ -684,6 +684,7 @@ uint64_t helper_ld_asi(CPUSPARCState *env,
target_ulong addr,
     case ASI_M_DIAGS:   /* Turbosparc DTLB Diagnostic */
     case ASI_M_IODIAG:  /* Turbosparc IOTLB Diagnostic */
         break;
+    case ASI_USERTXT: /* User code access */
     case ASI_KERNELTXT: /* Supervisor code access */
         oi = make_memop_idx(memop, cpu_mmu_index(env_cpu(env), true));
         switch (size) {
@@ -779,7 +780,6 @@ uint64_t helper_ld_asi(CPUSPARCState *env,
target_ulong addr,
     case 0x4c: /* SuperSPARC MMU Breakpoint Action */
         ret = env->mmubpaction;
         break;
-    case ASI_USERTXT: /* User code access, XXX */
     default:
         sparc_raise_mmu_fault(cs, addr, false, false, asi, size, GETPC());
         ret = 0;