[PATCH v10 24/28] record-btrace: extend unwinder

Markus Metzger
2014-01-14T08:04:52Z

Extend the always failing unwinder to provide the PC based on the call
structure detected in the branch trace.

The unwinder supports normal frames and tailcall frames.
Inline frames are not supported.

Reviewed-by: Eli Zaretskii

2013-04-24 Markus Metzger <markus.t.metzger@intel.com>

* record.h (record_btrace_frame_unwind)
(record_btrace_tailcall_frame_unwind): New declarations.
* dwarf2-frame: Include record.h
(dwarf2_frame_cfa): Throw an error for btrace frames.
* record-btrace.c: Include hashtab.h.
(btrace_get_bfun_name): New.
(btrace_call_history): Call btrace_get_bfun_name.
(struct btrace_frame_cache): New.
(bfcache): New.
(bfcache_hash, bfcache_eq, bfcache_new): New.
(btrace_get_frame_function): New.
(record_btrace_frame_unwind_stop_reason): Allow unwinding.
(record_btrace_frame_this_id): Compute own id.
(record_btrace_frame_prev_register): Provide PC, throw_error
for all other registers.
(record_btrace_frame_sniffer): Detect btrace frames.
(record_btrace_tailcall_frame_sniffer): New.
(record_btrace_frame_dealloc_cache): New.
(record_btrace_frame_unwind): Add new functions.
(record_btrace_tailcall_frame_unwind): New.
(_initialize_record_btrace): Allocate cache.
* btrace.c (btrace_clear): Call reinit_frame_cache.
* NEWS: Announce it.

testsuite/
* gdb.btrace/record_goto.exp: Add backtrace test.
* gdb.btrace/tailcall.exp: Add backtrace test.

---
gdb/NEWS | 2 +
gdb/btrace.c | 4 +
gdb/dwarf2-frame.c | 6 +
gdb/record-btrace.c | 288 +++++++++++++++++++++++++++++--
gdb/record.h | 4 +
gdb/testsuite/gdb.btrace/record_goto.exp | 12 ++
gdb/testsuite/gdb.btrace/tailcall.exp | 15 ++
7 files changed, 321 insertions(+), 10 deletions(-)

diff --git a/gdb/NEWS b/gdb/NEWS
index a031aba..506920e 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -114,6 +114,8 @@ info exceptions REGEXP
are listed.

* The btrace record target now supports the 'record goto' command.
+ For locations inside the execution trace, the back trace is computed
+ based on the information stored in the execution trace.

* New options

diff --git a/gdb/btrace.c b/gdb/btrace.c
index 632ebe1..ba87e16 100644
--- a/gdb/btrace.c
+++ b/gdb/btrace.c
@@ -765,6 +765,10 @@ btrace_clear (struct thread_info *tp)

DEBUG ("clear thread %d (%s)", tp->num, target_pid_to_str (tp->ptid));

+ /* Make sure btrace frames that may hold a pointer into the branch
+ trace data are destroyed. */
+ reinit_frame_cache ();
+
btinfo = &tp->btrace;

it = btinfo->begin;
diff --git a/gdb/dwarf2-frame.c b/gdb/dwarf2-frame.c
index 772de56..ce21112 100644
--- a/gdb/dwarf2-frame.c
+++ b/gdb/dwarf2-frame.c
@@ -31,6 +31,7 @@
#include "objfiles.h"
#include "regcache.h"
#include "value.h"
+#include "record.h"

#include "gdb_assert.h"
#include <string.h>
@@ -1510,6 +1511,11 @@ dwarf2_frame_base_sniffer (struct frame_info *this_frame)
CORE_ADDR
dwarf2_frame_cfa (struct frame_info *this_frame)
{
+ if (frame_unwinder_is (this_frame, &record_btrace_tailcall_frame_unwind)
+ || frame_unwinder_is (this_frame, &record_btrace_frame_unwind))
+ throw_error (NOT_AVAILABLE_ERROR,
+ _("cfa not available for record btrace target"));
+
while (get_frame_type (this_frame) == INLINE_FRAME)
this_frame = get_prev_frame (this_frame);
if (get_frame_unwind_stop_reason (this_frame) == UNWIND_UNAVAILABLE)
diff --git a/gdb/record-btrace.c b/gdb/record-btrace.c
index ce62cd5..07575f6 100644
--- a/gdb/record-btrace.c
+++ b/gdb/record-btrace.c
@@ -34,6 +34,7 @@
#include "filenames.h"
#include "regcache.h"
#include "frame-unwind.h"
+#include "hashtab.h"

/* The target_ops of record-btrace. */
static struct target_ops record_btrace_ops;
@@ -525,6 +526,28 @@ btrace_call_history_src_line (struct ui_out *uiout,
ui_out_field_int (uiout, "max line", end);
}

+/* Get the name of a branch trace function. */
+
+static const char *
+btrace_get_bfun_name (const struct btrace_function *bfun)
+{
+ struct minimal_symbol *msym;
+ struct symbol *sym;
+
+ if (bfun == NULL)
+ return "??";
+
+ msym = bfun->msym;
+ sym = bfun->sym;
+
+ if (sym != NULL)
+ return SYMBOL_PRINT_NAME (sym);
+ else if (msym != NULL)
+ return SYMBOL_PRINT_NAME (msym);
+ else
+ return "??";
+}
+
/* Disassemble a section of the recorded function trace. */

static void
@@ -546,8 +569,8 @@ btrace_call_history (struct ui_out *uiout,
struct symbol *sym;

bfun = btrace_call_get (&it);
- msym = bfun->msym;
sym = bfun->sym;
+ msym = bfun->msym;

/* Print the function index. */
ui_out_field_uint (uiout, "index", bfun->number);
@@ -966,13 +989,100 @@ record_btrace_prepare_to_store (struct target_ops *ops,
}
}

+/* The branch trace frame cache. */
+
+struct btrace_frame_cache
+{
+ /* The thread. */
+ struct thread_info *tp;
+
+ /* The frame info. */
+ struct frame_info *frame;
+
+ /* The branch trace function segment. */
+ const struct btrace_function *bfun;
+};
+
+/* A struct btrace_frame_cache hash table indexed by NEXT. */
+
+static htab_t bfcache;
+
+/* hash_f for htab_create_alloc of bfcache. */
+
+static hashval_t
+bfcache_hash (const void *arg)
+{
+ const struct btrace_frame_cache *cache = arg;
+
+ return htab_hash_pointer (cache->frame);
+}
+
+/* eq_f for htab_create_alloc of bfcache. */
+
+static int
+bfcache_eq (const void *arg1, const void *arg2)
+{
+ const struct btrace_frame_cache *cache1 = arg1;
+ const struct btrace_frame_cache *cache2 = arg2;
+
+ return cache1->frame == cache2->frame;
+}
+
+/* Create a new btrace frame cache. */
+
+static struct btrace_frame_cache *
+bfcache_new (struct frame_info *frame)
+{
+ struct btrace_frame_cache *cache;
+ void **slot;
+
+ cache = FRAME_OBSTACK_ZALLOC (struct btrace_frame_cache);
+ cache->frame = frame;
+
+ slot = htab_find_slot (bfcache, cache, INSERT);
+ gdb_assert (*slot == NULL);
+ *slot = cache;
+
+ return cache;
+}
+
+/* Extract the branch trace function from a branch trace frame. */
+
+static const struct btrace_function *
+btrace_get_frame_function (struct frame_info *frame)
+{
+ const struct btrace_frame_cache *cache;
+ const struct btrace_function *bfun;
+ struct btrace_frame_cache pattern;
+ void **slot;
+
+ pattern.frame = frame;
+
+ slot = htab_find_slot (bfcache, &pattern, NO_INSERT);
+ if (slot == NULL)
+ return NULL;
+
+ cache = *slot;
+ return cache->bfun;
+}
+
/* Implement stop_reason method for record_btrace_frame_unwind. */

static enum unwind_stop_reason
record_btrace_frame_unwind_stop_reason (struct frame_info *this_frame,
void **this_cache)
{
- return UNWIND_UNAVAILABLE;
+ const struct btrace_frame_cache *cache;
+ const struct btrace_function *bfun;
+
+ cache = *this_cache;
+ bfun = cache->bfun;
+ gdb_assert (bfun != NULL);
+
+ if (bfun->up == NULL)
+ return UNWIND_UNAVAILABLE;
+
+ return UNWIND_NO_REASON;
}

/* Implement this_id method for record_btrace_frame_unwind. */
@@ -981,7 +1091,27 @@ static void
record_btrace_frame_this_id (struct frame_info *this_frame, void **this_cache,
struct frame_id *this_id)
{
- /* Leave there the outer_frame_id value. */
+ const struct btrace_frame_cache *cache;
+ const struct btrace_function *bfun;
+ CORE_ADDR code, special;
+
+ cache = *this_cache;
+
+ bfun = cache->bfun;
+ gdb_assert (bfun != NULL);
+
+ while (bfun->segment.prev != NULL)
+ bfun = bfun->segment.prev;
+
+ code = get_frame_func (this_frame);
+ special = bfun->number;
+
+ *this_id = frame_id_build_unavailable_stack_special (code, special);
+
+ DEBUG ("[frame] %s id: (!stack, pc=%s, special=%s)",
+ btrace_get_bfun_name (cache->bfun),
+ core_addr_to_string_nz (this_id->code_addr),
+ core_addr_to_string_nz (this_id->special_addr));
}

/* Implement prev_register method for record_btrace_frame_unwind. */
@@ -991,8 +1121,46 @@ record_btrace_frame_prev_register (struct frame_info *this_frame,
void **this_cache,
int regnum)
{
- throw_error (NOT_AVAILABLE_ERROR,
- _("Registers are not available in btrace record history"));
+ const struct btrace_frame_cache *cache;
+ const struct btrace_function *bfun, *caller;
+ const struct btrace_insn *insn;
+ struct gdbarch *gdbarch;
+ CORE_ADDR pc;
+ int pcreg;
+
+ gdbarch = get_frame_arch (this_frame);
+ pcreg = gdbarch_pc_regnum (gdbarch);
+ if (pcreg < 0 || regnum != pcreg)
+ throw_error (NOT_AVAILABLE_ERROR,
+ _("Registers are not available in btrace record history"));
+
+ cache = *this_cache;
+ bfun = cache->bfun;
+ gdb_assert (bfun != NULL);
+
+ caller = bfun->up;
+ if (caller == NULL)
+ throw_error (NOT_AVAILABLE_ERROR,
+ _("No caller in btrace record history"));
+
+ if ((bfun->flags & BFUN_UP_LINKS_TO_RET) != 0)
+ {
+ insn = VEC_index (btrace_insn_s, caller->insn, 0);
+ pc = insn->pc;
+ }
+ else
+ {
+ insn = VEC_last (btrace_insn_s, caller->insn);
+ pc = insn->pc;
+
+ pc += gdb_insn_length (gdbarch, pc);
+ }
+
+ DEBUG ("[frame] unwound PC in %s on level %d: %s",
+ btrace_get_bfun_name (bfun), bfun->level,
+ core_addr_to_string_nz (pc));
+
+ return frame_unwind_got_address (this_frame, regnum, pc);
}

/* Implement sniffer method for record_btrace_frame_unwind. */
@@ -1002,15 +1170,99 @@ record_btrace_frame_sniffer (const struct frame_unwind *self,
struct frame_info *this_frame,
void **this_cache)
{
+ const struct btrace_function *bfun;
+ struct btrace_frame_cache *cache;
struct thread_info *tp;
- struct btrace_thread_info *btinfo;
- struct btrace_insn_iterator *replay;
+ struct frame_info *next;

/* THIS_FRAME does not contain a reference to its thread. */
tp = find_thread_ptid (inferior_ptid);
gdb_assert (tp != NULL);

- return btrace_is_replaying (tp);
+ bfun = NULL;
+ next = get_next_frame (this_frame);
+ if (next == NULL)
+ {
+ const struct btrace_insn_iterator *replay;
+
+ replay = tp->btrace.replay;
+ if (replay != NULL)
+ bfun = replay->function;
+ }
+ else
+ {
+ const struct btrace_function *callee;
+
+ callee = btrace_get_frame_function (next);
+ if (callee != NULL && (callee->flags & BFUN_UP_LINKS_TO_TAILCALL) == 0)
+ bfun = callee->up;
+ }
+
+ if (bfun == NULL)
+ return 0;
+
+ DEBUG ("[frame] sniffed frame for %s on level %d",
+ btrace_get_bfun_name (bfun), bfun->level);
+
+ /* This is our frame. Initialize the frame cache. */
+ cache = bfcache_new (this_frame);
+ cache->tp = tp;
+ cache->bfun = bfun;
+
+ *this_cache = cache;
+ return 1;
+}
+
+/* Implement sniffer method for record_btrace_tailcall_frame_unwind. */
+
+static int
+record_btrace_tailcall_frame_sniffer (const struct frame_unwind *self,
+ struct frame_info *this_frame,
+ void **this_cache)
+{
+ const struct btrace_function *bfun, *callee;
+ struct btrace_frame_cache *cache;
+ struct frame_info *next;
+
+ next = get_next_frame (this_frame);
+ if (next == NULL)
+ return 0;
+
+ callee = btrace_get_frame_function (next);
+ if (callee == NULL)
+ return 0;
+
+ if ((callee->flags & BFUN_UP_LINKS_TO_TAILCALL) == 0)
+ return 0;
+
+ bfun = callee->up;
+ if (bfun == NULL)
+ return 0;
+
+ DEBUG ("[frame] sniffed tailcall frame for %s on level %d",
+ btrace_get_bfun_name (bfun), bfun->level);
+
+ /* This is our frame. Initialize the frame cache. */
+ cache = bfcache_new (this_frame);
+ cache->tp = find_thread_ptid (inferior_ptid);
+ cache->bfun = bfun;
+
+ *this_cache = cache;
+ return 1;
+}
+
+static void
+record_btrace_frame_dealloc_cache (struct frame_info *self, void *this_cache)
+{
+ struct btrace_frame_cache *cache;
+ void **slot;
+
+ cache = this_cache;
+
+ slot = htab_find_slot (bfcache, cache, NO_INSERT);
+ gdb_assert (slot != NULL);
+
+ htab_remove_elt (bfcache, cache);
}

/* btrace recording does not store previous memory content, neither the stack
@@ -1019,14 +1271,26 @@ record_btrace_frame_sniffer (const struct frame_unwind *self,
Therefore this unwinder reports any possibly unwound registers as
<unavailable>. */

-static const struct frame_unwind record_btrace_frame_unwind =
+const struct frame_unwind record_btrace_frame_unwind =
{
NORMAL_FRAME,
record_btrace_frame_unwind_stop_reason,
record_btrace_frame_this_id,
record_btrace_frame_prev_register,
NULL,
- record_btrace_frame_sniffer
+ record_btrace_frame_sniffer,
+ record_btrace_frame_dealloc_cache
+};
+
+const struct frame_unwind record_btrace_tailcall_frame_unwind =
+{
+ TAILCALL_FRAME,
+ record_btrace_frame_unwind_stop_reason,
+ record_btrace_frame_this_id,
+ record_btrace_frame_prev_register,
+ NULL,
+ record_btrace_tailcall_frame_sniffer,
+ record_btrace_frame_dealloc_cache
};

/* The to_resume method of target record-btrace. */
@@ -1233,6 +1497,7 @@ init_record_btrace_ops (void)
ops->to_store_registers = record_btrace_store_registers;
ops->to_prepare_to_store = record_btrace_prepare_to_store;
ops->to_get_unwinder = &record_btrace_frame_unwind;
+ ops->to_get_tailcall_unwinder = &record_btrace_tailcall_frame_unwind;
ops->to_resume = record_btrace_resume;
ops->to_wait = record_btrace_wait;
ops->to_find_new_threads = record_btrace_find_new_threads;
@@ -1269,4 +1534,7 @@ _initialize_record_btrace (void)

init_record_btrace_ops ();
add_target (&record_btrace_ops);
+
+ bfcache = htab_create_alloc (50, bfcache_hash, bfcache_eq, NULL,
+ xcalloc, xfree);
}
diff --git a/gdb/record.h b/gdb/record.h
index 18263fc..063ed96 100644
--- a/gdb/record.h
+++ b/gdb/record.h
@@ -32,6 +32,10 @@ extern struct cmd_list_element *set_record_cmdlist;
extern struct cmd_list_element *show_record_cmdlist;
extern struct cmd_list_element *info_record_cmdlist;

+/* Unwinders for some record targets. */
+extern const struct frame_unwind record_btrace_frame_unwind;
+extern const struct frame_unwind record_btrace_tailcall_frame_unwind;
+
/* A list of flags specifying what record target methods should print. */
enum record_print_flag
{
diff --git a/gdb/testsuite/gdb.btrace/record_goto.exp b/gdb/testsuite/gdb.btrace/record_goto.exp
index eb07b9b..ab69bef 100644
--- a/gdb/testsuite/gdb.btrace/record_goto.exp
+++ b/gdb/testsuite/gdb.btrace/record_goto.exp
@@ -87,6 +87,18 @@ gdb_test "record instruction-history" [join [list \
# let's go to another place in the history
gdb_test "record goto 26" ".*fun3 \\(\\) at record_goto.c:35.*"

+# check the back trace at that location
+gdb_test "backtrace" [join [list \
+ "#0.*fun3.*at record_goto.c:35.*" \
+ "#1.*fun4.*at record_goto.c:43.*" \
+ "#2.*main.*at record_goto.c:49.*" \
+ "Backtrace stopped: not enough registers or memory available to unwind further" \
+ ] "\r\n"]
+
+# walk the backtrace
+gdb_test "up" ".*fun4.*at record_goto.c:43.*" "up to fun4"
+gdb_test "up" ".*main.*at record_goto.c:49.*" "up to main"
+
# the function call history should start at the new location
gdb_test "record function-call-history /ci -" [join [list \
"8\t fun3\tinst 19,21" \
diff --git a/gdb/testsuite/gdb.btrace/tailcall.exp b/gdb/testsuite/gdb.btrace/tailcall.exp
index c965675..a001783 100644
--- a/gdb/testsuite/gdb.btrace/tailcall.exp
+++ b/gdb/testsuite/gdb.btrace/tailcall.exp
@@ -60,3 +60,18 @@ gdb_test "record function-call-history /c 1" [join [list \
"2\t bar" \
"3\tmain" \
] "\r\n"] "indented"
+
+# go into bar
+gdb_test "record goto 3" ".*bar \\(\\) at .*x86-tailcall.c:24\r\n.*"
+
+# check the backtrace
+gdb_test "backtrace" [join [list \
+ "#0.*bar \\(\\) at x86-tailcall.c:24" \
+ "#1.*foo \\(\\) at x86-tailcall.c:29" \
+ "#2.*main \\(\\) at x86-tailcall.c:37" \
+ "Backtrace stopped: not enough registers or memory available to unwind further" \
+ ] "\r\n"]
+
+# walk the backtrace
+gdb_test "up" "#1\[^\r\n\]*foo \\(\\) at x86-tailcall.c:29\r\n.*" "up to foo"
+gdb_test "up" "#2\[^\r\n\]*main \\(\\) at x86-tailcall.c:37\r\n.*" "up to main"
--
1.8.3.1