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S/390: displaced stepping and PC-relative RIL-b/RIL-c instructions

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This adds displaced stepping support for the General-Instruction
Extension Facility instructions, which have a PC-relative displacement
(RIL-b/RIL-c).  We already handle RIL branches, but not others.

Currently, displaced stepping a breakpoint put on any of these
instructions results in the inferior crashing when or after the
instruction is executed out-of-line in the scratch pad.

This patch takes the easy route of patching the displacement in the
copy of the instruction in the scratch pad.  As the displacement is a
signed 32-bit field, it's possible that the stratch pad ends too far
that the needed displacement doesn't fit in the adjusted instruction,
as e.g., if stepping over a breakpoint in a shared library (the
scratch pad is around the main program's entry point).  That case is
detected and GDB falls back to stepping over the breakpoint in-line
(which involves pausing all threads momentarily).

(We could probably do something smarter, but I don't plan on doing it
myself.  This was already sufficient to get "maint set target-non-stop
on" working regression free on S/390.)

Tested on S/390 RHEL 7.1, where it fixes a few hundred FAILs when
testing with displaced stepping force-enabled, with the end result
being no regressions compared to a test run that doesn't force
displaced stepping.  Fixes the non-stop tests compared to mainline
too; most are crashing due to this on the machine I run tests on.

gdb/ChangeLog:
2015-08-07  Pedro Alves  <palves@redhat.com>

	* s390-linux-tdep.c (is_non_branch_ril)
	(s390_displaced_step_copy_insn): New functions.
	(s390_displaced_step_fixup): Update comment.
	(s390_gdbarch_init): Install s390_displaced_step_copy_insn as
	gdbarch_displaced_step_copy_insn hook.
This commit is contained in:
Pedro Alves 2015-08-06 18:23:01 +01:00
parent 7f03bd92e3
commit 5ac213430b
2 changed files with 120 additions and 3 deletions
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8
gdb/ChangeLog
View File

@ -1,3 +1,11 @@
2015-08-07 Pedro Alves <palves@redhat.com>
* s390-linux-tdep.c (is_non_branch_ril)
(s390_displaced_step_copy_insn): New functions.
(s390_displaced_step_fixup): Update comment.
(s390_gdbarch_init): Install s390_displaced_step_copy_insn as
gdbarch_displaced_step_copy_insn hook.
2015-08-07 Pedro Alves <palves@redhat.com>
* infrun.c (displaced_step_prepare_throw): Return -1 if

115
gdb/s390-linux-tdep.c
View File

@ -1539,6 +1539,116 @@ s390_stack_frame_destroyed_p (struct gdbarch *gdbarch, CORE_ADDR pc)
/* Displaced stepping. */
/* Return true if INSN is a non-branch RIL-b or RIL-c format
instruction. */
static int
is_non_branch_ril (gdb_byte *insn)
{
gdb_byte op1 = insn[0];
if (op1 == 0xc4)
{
gdb_byte op2 = insn[1] & 0x0f;
switch (op2)
{
case 0x02: /* llhrl */
case 0x04: /* lghrl */
case 0x05: /* lhrl */
case 0x06: /* llghrl */
case 0x07: /* sthrl */
case 0x08: /* lgrl */
case 0x0b: /* stgrl */
case 0x0c: /* lgfrl */
case 0x0d: /* lrl */
case 0x0e: /* llgfrl */
case 0x0f: /* strl */
return 1;
}
}
else if (op1 == 0xc6)
{
gdb_byte op2 = insn[1] & 0x0f;
switch (op2)
{
case 0x00: /* exrl */
case 0x02: /* pfdrl */
case 0x04: /* cghrl */
case 0x05: /* chrl */
case 0x06: /* clghrl */
case 0x07: /* clhrl */
case 0x08: /* cgrl */
case 0x0a: /* clgrl */
case 0x0c: /* cgfrl */
case 0x0d: /* crl */
case 0x0e: /* clgfrl */
case 0x0f: /* clrl */
return 1;
}
}
return 0;
}
/* Implementation of gdbarch_displaced_step_copy_insn. */
static struct displaced_step_closure *
s390_displaced_step_copy_insn (struct gdbarch *gdbarch,
CORE_ADDR from, CORE_ADDR to,
struct regcache *regs)
{
size_t len = gdbarch_max_insn_length (gdbarch);
gdb_byte *buf = xmalloc (len);
struct cleanup *old_chain = make_cleanup (xfree, buf);
read_memory (from, buf, len);
/* Adjust the displacement field of PC-relative RIL instructions,
except branches. The latter are handled in the fixup hook. */
if (is_non_branch_ril (buf))
{
LONGEST offset;
offset = extract_signed_integer (buf + 2, 4, BFD_ENDIAN_BIG);
offset = (from - to + offset * 2) / 2;
/* If the instruction is too far from the jump pad, punt. This
will usually happen with instructions in shared libraries.
We could probably support these by rewriting them to be
absolute or fully emulating them. */
if (offset < INT32_MIN || offset > INT32_MAX)
{
/* Let the core fall back to stepping over the breakpoint
in-line. */
if (debug_displaced)
{
fprintf_unfiltered (gdb_stdlog,
"displaced: can't displaced step "
"RIL instruction: offset %s out of range\n",
plongest (offset));
}
do_cleanups (old_chain);
return NULL;
}
store_signed_integer (buf + 2, 4, BFD_ENDIAN_BIG, offset);
}
write_memory (to, buf, len);
if (debug_displaced)
{
fprintf_unfiltered (gdb_stdlog, "displaced: copy %s->%s: ",
paddress (gdbarch, from), paddress (gdbarch, to));
displaced_step_dump_bytes (gdb_stdlog, buf, len);
}
discard_cleanups (old_chain);
return (struct displaced_step_closure *) buf;
}
/* Fix up the state of registers and memory after having single-stepped
a displaced instruction. */
static void
@ -1547,8 +1657,7 @@ s390_displaced_step_fixup (struct gdbarch *gdbarch,
CORE_ADDR from, CORE_ADDR to,
struct regcache *regs)
{
/* Since we use simple_displaced_step_copy_insn, our closure is a
copy of the instruction. */
/* Our closure is a copy of the instruction. */
gdb_byte *insn = (gdb_byte *) closure;
static int s390_instrlen[] = { 2, 4, 4, 6 };
int insnlen = s390_instrlen[insn[0] >> 6];
@ -3285,7 +3394,7 @@ s390_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
/* Displaced stepping. */
set_gdbarch_displaced_step_copy_insn (gdbarch,
simple_displaced_step_copy_insn);
s390_displaced_step_copy_insn);
set_gdbarch_displaced_step_fixup (gdbarch, s390_displaced_step_fixup);
set_gdbarch_displaced_step_free_closure (gdbarch,
simple_displaced_step_free_closure);