* [pushed] [gdb/tdep] Fix larl handling in s390_displaced_step_fixup
@ 2022-12-10 14:41 Tom de Vries
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From: Tom de Vries @ 2022-12-10 14:41 UTC (permalink / raw)
To: gdb-patches; +Cc: Ulrich Weigand
On s390x-linux with target board unix/-m31, I run into:
...
(gdb) PASS: gdb.guile/scm-lazy-string.exp: bad length
print ptr^M
$1 = 0x804006b0 <error: Cannot access memory at address 0x804006b0>^M
(gdb) FAIL: gdb.guile/scm-lazy-string.exp: ptr: print ptr
...
A minimal example is:
...
$ gdb -q -batch -ex "set trace-commands on" -x gdb.in
+file scm-lazy-string
+break main
Breakpoint 1 at 0x4005d2: file scm-lazy-string.c, line 23.
+run
Breakpoint 1, main () at scm-lazy-string.c:23
23 const char *ptr = "pointer";
+step
24 const char array[] = "array";
+print ptr
$1 = 0x804006b0 <error: Cannot access memory at address 0x804006b0>
...
If we delete the breakpoint after running to it, we have instead the expected:
...
+delete
+step
24 const char array[] = "array";
+print ptr
$1 = 0x4006b0 "pointer"
...
The problem is in displaced stepping, forced by the presence of the breakpoint,
when stepping over this insn:
...
0x4005d2 <main+10> larl %r1,0x4006b0
...
With normal stepping we have:
...
(gdb) p /x $r1
$2 = 0x3ff004006b0
...
but with displaced stepping we have instead (note the 0x80000000 difference):
...
(gdb) p /x $r1
$1 = 0x3ff804006b0
(gdb)
...
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.
Fix this by removing the "amode |".
Tested on s390-linux, with native and target board unix/-m31.
Approved-By: Ulrich Weigand <uweigand@de.ibm.com>
---
gdb/s390-tdep.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/gdb/s390-tdep.c b/gdb/s390-tdep.c
index d0dba7654bb..2486ecdcb3a 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. */
base-commit: b813665fd2ec3a5cbe7cbc8b36ce7aa0271dec44
--
2.35.3
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2022-12-10 14:41 [pushed] [gdb/tdep] Fix larl handling in s390_displaced_step_fixup Tom de Vries
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