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From: "vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug tdep/29867] [gdb/tdep, s390x -m31] FAIL:
 gdb.guile/scm-lazy-string.exp: ptr: print ptr
Date: Fri, 09 Dec 2022 13:25:47 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D29867

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |arnez at linux dot ibm.com,
                   |                            |cel at us dot ibm.com,
                   |                            |ulrich.weigand at de dot i=
bm.com

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
The problem is in displaced stepping over insn:
...
=E2=94=82B+> 0x4005d2 <main+10>      larl    %r1,0x4006b0=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
             =E2=94=82...

In the failing case we have:
...
(gdb) si
(gdb) p /x $r1
$1 =3D 0x3ff804006b0
(gdb)=20
...

In the passing case we have:
...
(gdb) si
(gdb) p /x $r1
$2 =3D 0x3ff004006b0
...

The difference comes from this code in s390_displaced_step_fixup:
...
  /* Handle LOAD ADDRESS RELATIVE LONG.  */
  else if (is_ril (insn, op1_larl, op2_larl, &r1, &i2))
    {
      /* Update PC.  */
      regcache_write_pc (regs, from + insnlen);
      /* Recompute output address in R1.  */
      regcache_cooked_write_unsigned (regs, S390_R0_REGNUM + r1,
                                      amode | (from + i2 * 2));
    }
...
where the "amode |" adds the 0x80000000.

Using this patch:
...
diff --git a/gdb/s390-tdep.c b/gdb/s390-tdep.c
index d0dba7654bb..11b309dc817 100644
--- a/gdb/s390-tdep.c
+++ b/gdb/s390-tdep.c
@@ -557,7 +557,7 @@ s390_displaced_step_fixup (struct gdbarch *gdbarch,
       regcache_write_pc (regs, from + insnlen);
       /* Recompute output address in R1.  */
       regcache_cooked_write_unsigned (regs, S390_R0_REGNUM + r1,
-                                     amode | (from + i2 * 2));
+                                     (from + i2 * 2));
     }

   /* If we executed a breakpoint instruction, point PC right back at it.  =
*/
...
the test-case passes.

I don't understand the architecture well enough to decide what the root cau=
se
is and whether this patch addresses it.

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