[PATCH v3 15/17] PPC64: Fix gdb.arch/ppc64-atomic-inst.exp with displaced stepping

Pedro Alves
2015-04-17T10:45:43Z

The ppc64 displaced step code can't handle atomic sequences. Fallback
to stepping over the breakpoint in-line if we detect one.

gdb/ChangeLog:
2015-04-17 Pedro Alves <palves@redhat.com>

* infrun.c (displaced_step_prepare): Return -1 if
gdbarch_displaced_step_copy_insn returns NULL.
(resume): When displaced stepping doesn't work, try software
single-stepping.
* rs6000-tdep.c (LWARX_MASK, LWARX_INSTRUCTION, LDARX_INSTRUCTION)
(STWCX_MASK, STWCX_INSTRUCTION, STDCX_INSTRUCTION): Move higher up
in file.
(ppc_displaced_step_copy_insn): New function.
(ppc_displaced_step_fixup): Update comment.
(rs6000_gdbarch_init): Install ppc_displaced_step_copy_insn as
gdbarch_displaced_step_copy_insn hook.
* gdbarch.sh (displaced_step_copy_insn): Document what happens on
NULL return.
* gdbarch.h: Regenerate.

gdb/testsuite/ChangeLog:
2015-04-17 Pedro Alves <palves@redhat.com>

* gdb.arch/ppc64-atomic-inst.exp (do_test): New procedure, move
tests here.
(top level): Run do_test with and without displaced stepping.

v3:

- Document that gdbarch_displaced_step_copy_insn can return NULL.
---
gdb/gdbarch.h | 6 ++-
gdb/gdbarch.sh | 4 ++
gdb/infrun.c | 11 +++--
gdb/rs6000-tdep.c | 68 +++++++++++++++++++++++-----
gdb/testsuite/gdb.arch/ppc64-atomic-inst.exp | 50 ++++++++++++--------
5 files changed, 106 insertions(+), 33 deletions(-)

diff --git a/gdb/gdbarch.h b/gdb/gdbarch.h
index c94c19c..b02225a 100644
--- a/gdb/gdbarch.h
+++ b/gdb/gdbarch.h
@@ -923,7 +923,11 @@ extern void set_gdbarch_max_insn_length (struct gdbarch *gdbarch, ULONGEST max_i

If your architecture doesn't need to adjust instructions before
single-stepping them, consider using simple_displaced_step_copy_insn
- here. */
+ here.
+
+ If the instruction cannot execute out of line, return NULL. The
+ core falls back to stepping past the instruction in-line instead in
+ that case. */

extern int gdbarch_displaced_step_copy_insn_p (struct gdbarch *gdbarch);

diff --git a/gdb/gdbarch.sh b/gdb/gdbarch.sh
index 0f303a4..749cbda 100755
--- a/gdb/gdbarch.sh
+++ b/gdb/gdbarch.sh
@@ -763,6 +763,10 @@ V:ULONGEST:max_insn_length:::0:0
# If your architecture doesn't need to adjust instructions before
# single-stepping them, consider using simple_displaced_step_copy_insn
# here.
+#
+# If the instruction cannot execute out of line, return NULL. The
+# core falls back to stepping past the instruction in-line instead in
+# that case.
M:struct displaced_step_closure *:displaced_step_copy_insn:CORE_ADDR from, CORE_ADDR to, struct regcache *regs:from, to, regs

# Return true if GDB should use hardware single-stepping to execute
diff --git a/gdb/infrun.c b/gdb/infrun.c
index be186a7..a89eefc 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1797,9 +1797,14 @@ displaced_step_prepare_throw (ptid_t ptid)

closure = gdbarch_displaced_step_copy_insn (gdbarch,
original, copy, regcache);
-
- /* We don't support the fully-simulated case at present. */
- gdb_assert (closure);
+ if (closure == NULL)
+ {
+ /* The architecture doesn't know how or want to displaced step
+ this instruction or instruction sequence. Fallback to
+ stepping over the breakpoint in-line. */
+ do_cleanups (old_cleanups);
+ return -1;
+ }

/* Save the information we need to fix things up if the step
succeeds. */
diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
index a125000..6106029 100644
--- a/gdb/rs6000-tdep.c
+++ b/gdb/rs6000-tdep.c
@@ -974,6 +974,61 @@ rs6000_breakpoint_from_pc (struct gdbarch *gdbarch, CORE_ADDR *bp_addr,
#define BXL_INSN 0x4c000000
#define BP_INSN 0x7C000008

+/* Instruction masks used during single-stepping of atomic
+ sequences. */
+#define LWARX_MASK 0xfc0007fe
+#define LWARX_INSTRUCTION 0x7c000028
+#define LDARX_INSTRUCTION 0x7c0000A8
+#define STWCX_MASK 0xfc0007ff
+#define STWCX_INSTRUCTION 0x7c00012d
+#define STDCX_INSTRUCTION 0x7c0001ad
+
+/* We can't displaces step atomic sequenes. Otherwise this is just
+ simple_displaced_step_copy_insn. */
+
+static struct displaced_step_closure *
+ppc_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);
+ enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
+ int insn;
+
+ read_memory (from, buf, len);
+
+ insn = extract_signed_integer (buf, PPC_INSN_SIZE, byte_order);
+
+ /* Assume all atomic sequences start with a lwarx/ldarx instruction. */
+ if ((insn & LWARX_MASK) == LWARX_INSTRUCTION
+ || (insn & LWARX_MASK) == LDARX_INSTRUCTION)
+ {
+ if (debug_displaced)
+ {
+ fprintf_unfiltered (gdb_stdlog,
+ "displaced: can't displaced step "
+ "atomic sequence at %s\n",
+ paddress (gdbarch, from));
+ }
+ do_cleanups (old_chain);
+ return NULL;
+ }
+
+ 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
@@ -983,8 +1038,7 @@ ppc_displaced_step_fixup (struct gdbarch *gdbarch,
struct regcache *regs)
{
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
- /* Since we use simple_displaced_step_copy_insn, our closure is a
- copy of the instruction. */
+ /* Our closure is a copy of the instruction. */
ULONGEST insn = extract_unsigned_integer ((gdb_byte *) closure,
PPC_INSN_SIZE, byte_order);
ULONGEST opcode = 0;
@@ -1077,14 +1131,6 @@ ppc_displaced_step_hw_singlestep (struct gdbarch *gdbarch,
return 1;
}

-/* Instruction masks used during single-stepping of atomic sequences. */
-#define LWARX_MASK 0xfc0007fe
-#define LWARX_INSTRUCTION 0x7c000028
-#define LDARX_INSTRUCTION 0x7c0000A8
-#define STWCX_MASK 0xfc0007ff
-#define STWCX_INSTRUCTION 0x7c00012d
-#define STDCX_INSTRUCTION 0x7c0001ad
-
/* Checks for an atomic sequence of instructions beginning with a LWARX/LDARX
instruction and ending with a STWCX/STDCX instruction. If such a sequence
is found, attempt to step through it. A breakpoint is placed at the end of
@@ -5923,7 +5969,7 @@ rs6000_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)

/* Setup displaced stepping. */
set_gdbarch_displaced_step_copy_insn (gdbarch,
- simple_displaced_step_copy_insn);
+ ppc_displaced_step_copy_insn);
set_gdbarch_displaced_step_hw_singlestep (gdbarch,
ppc_displaced_step_hw_singlestep);
set_gdbarch_displaced_step_fixup (gdbarch, ppc_displaced_step_fixup);
diff --git a/gdb/testsuite/gdb.arch/ppc64-atomic-inst.exp b/gdb/testsuite/gdb.arch/ppc64-atomic-inst.exp
index d251425..08518fb 100644
--- a/gdb/testsuite/gdb.arch/ppc64-atomic-inst.exp
+++ b/gdb/testsuite/gdb.arch/ppc64-atomic-inst.exp
@@ -32,27 +32,41 @@ if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile} {debug quiet}]
return -1
}

-if ![runto_main] then {
- untested "could not run to main"
- return -1
-}
+# The test proper. DISPLACED is true if we should try with displaced
+# stepping.
+proc do_test { displaced } {
+ global decimal hex
+
+ if ![runto_main] then {
+ untested "could not run to main"
+ return -1
+ }
+
+ gdb_test_no_output "set displaced-stepping $displaced"

-set bp1 [gdb_get_line_number "lwarx"]
-gdb_breakpoint "$bp1" "Breakpoint $decimal at $hex" \
- "Set the breakpoint at the start of the lwarx/stwcx sequence"
+ set bp1 [gdb_get_line_number "lwarx"]
+ gdb_breakpoint "$bp1" "Breakpoint $decimal at $hex" \
+ "Set the breakpoint at the start of the lwarx/stwcx sequence"

-set bp2 [gdb_get_line_number "ldarx"]
-gdb_breakpoint "$bp2" "Breakpoint $decimal at $hex" \
- "Set the breakpoint at the start of the ldarx/stdcx sequence"
+ set bp2 [gdb_get_line_number "ldarx"]
+ gdb_breakpoint "$bp2" "Breakpoint $decimal at $hex" \
+ "Set the breakpoint at the start of the ldarx/stdcx sequence"

-gdb_test continue "Continuing.*Breakpoint $decimal.*" \
- "Continue until lwarx/stwcx start breakpoint"
+ gdb_test continue "Continuing.*Breakpoint $decimal.*" \
+ "Continue until lwarx/stwcx start breakpoint"

-gdb_test nexti "bne.*1b" \
- "Step through the lwarx/stwcx sequence"
+ gdb_test nexti "bne.*1b" \
+ "Step through the lwarx/stwcx sequence"

-gdb_test continue "Continuing.*Breakpoint $decimal.*" \
- "Continue until ldarx/stdcx start breakpoint"
+ gdb_test continue "Continuing.*Breakpoint $decimal.*" \
+ "Continue until ldarx/stdcx start breakpoint"

-gdb_test nexti "bne.*1b" \
- "Step through the ldarx/stdcx sequence"
+ gdb_test nexti "bne.*1b" \
+ "Step through the ldarx/stdcx sequence"
+}
+
+foreach displaced { "off" "on" } {
+ with_test_prefix "displaced=$displaced" {
+ do_test $displaced
+ }
+}
--
1.9.3