[PATCH 5/6] New JIT unwinder.

Sanjoy Das
2011-08-20T06:27:05Z

Introduce a "proxy unwinder", whcih will pass down all calls to the
functions the JIT reader provides.

gdb/ChangeLog

* jit.c (jut_unwind_reg_set_impl, free_reg_value_impl)
(jit_unwind_reg_get_impl, jit_frame_sniffer)
(jit_frame_unwind_stop_reason, jit_frame_this_id)
(jit_frame_prev_register, jit_dealloc_cache)
(jit_gdbarch_data_init): New functions
(_initialize_jit): Register new gdbarch data slot
jit_gdbarch_data.
---
gdb/ChangeLog | 10 ++
gdb/jit.c | 260 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 270 insertions(+), 0 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 70c280e..92d645b 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,15 @@
2011-08-20 Sanjoy Das <sdas@igalia.com>

+ * jit.c (jut_unwind_reg_set_impl, free_reg_value_impl)
+ (jit_unwind_reg_get_impl, jit_frame_sniffer)
+ (jit_frame_unwind_stop_reason, jit_frame_this_id)
+ (jit_frame_prev_register, jit_dealloc_cache)
+ (jit_gdbarch_data_init): New functions
+ (_initialize_jit): Register new gdbarch data slot
+ jit_gdbarch_data.
+
+2011-08-20 Sanjoy Das <sdas@igalia.com>
+
* jit.c (add_objfile_entry, jit_target_read_impl)
(jit_object_open_impl, jit_symtab_open_impl, compare_block)
(jit_block_open_impl, jit_block_open_impl)
diff --git a/gdb/jit.c b/gdb/jit.c
index d4d7ddb..da39525 100644
--- a/gdb/jit.c
+++ b/gdb/jit.c
@@ -31,6 +31,7 @@
#include "inferior.h"
#include "observer.h"
#include "objfiles.h"
+#include "regcache.h"
#include "symfile.h"
#include "symtab.h"
#include "target.h"
@@ -49,6 +50,12 @@ static const struct inferior_data *jit_inferior_data = NULL;

static void jit_inferior_init (struct gdbarch *gdbarch);

+/* An unwinder is registered for every gdbarch. This key is used to
+ remember if the unwinder has been registered for a particular
+ gdbarch. */
+
+static struct gdbarch_data *jit_gdbarch_data;
+
/* Non-zero if we want to see trace of jit level stuff. */

static int jit_debug = 0;
@@ -907,6 +914,244 @@ jit_breakpoint_re_set_internal (struct gdbarch *gdbarch,
return 0;
}

+/* The private data passed around in the frame unwind callback
+ functions. */
+
+struct jit_unwind_private
+{
+ /* Cached register values. See jit_frame_sniffer to see how this
+ works. */
+
+ struct gdb_reg_value **registers;
+
+ /* The frame being unwound. */
+
+ struct frame_info *this_frame;
+};
+
+/* Sets the value of a particular register in this frame. */
+
+static void
+jit_unwind_reg_set_impl (struct gdb_unwind_callbacks *cb, int regnum,
+ struct gdb_reg_value *value)
+{
+ struct jit_unwind_private *priv;
+ int gdb_reg;
+
+ gdb_reg = gdbarch_dwarf2_reg_to_regnum (target_gdbarch, regnum);
+ priv = cb->priv_data;
+ gdb_assert (priv->registers);
+ priv->registers[gdb_reg] = value;
+}
+
+/* Passed in the `free' field of a gdb_reg_value. */
+
+static void
+free_reg_value_impl (struct gdb_reg_value *reg_value)
+{
+ xfree (reg_value);
+}
+
+/* Get the value of register REGNUM in the previous frame. */
+
+static struct gdb_reg_value *
+jit_unwind_reg_get_impl (struct gdb_unwind_callbacks *cb, int regnum)
+{
+ struct jit_unwind_private *priv;
+ struct gdb_reg_value *value;
+ int gdb_reg, size;
+
+ priv = cb->priv_data;
+ gdb_reg = gdbarch_dwarf2_reg_to_regnum (target_gdbarch, regnum);
+ size = register_size (target_gdbarch, gdb_reg);
+ value = xmalloc (sizeof (struct gdb_reg_value) + size - 1);
+ value->defined = frame_register_read (priv->this_frame, gdb_reg,
+ value->value);
+ value->size = size;
+ value->free = free_reg_value_impl;
+ return value;
+}
+
+/* The frame sniffer for the pseudo unwinder.
+
+ While this is nominally a frame sniffer, in the case where the JIT
+ reader actually recognizes the frame, it does a lot more work -- it
+ unwinds the frame and saves the corresponding register values in
+ the cache. jit_frame_prev_register simply returns the saved
+ register values. */
+
+static int
+jit_frame_sniffer (const struct frame_unwind *self,
+ struct frame_info *this_frame, void **cache)
+{
+ struct jit_inferior_data *inf_data;
+ struct jit_unwind_private *priv_data;
+ struct jit_dbg_reader *iter;
+ struct gdb_unwind_callbacks callbacks;
+ struct gdb_reader_funcs *funcs;
+
+ inf_data = get_jit_inferior_data ();
+
+ callbacks.reg_get = jit_unwind_reg_get_impl;
+ callbacks.reg_set = jit_unwind_reg_set_impl;
+ callbacks.target_read = jit_target_read_impl;
+
+ if (loaded_jit_reader == NULL)
+ return 0;
+
+ funcs = loaded_jit_reader->functions;
+
+ if (!*cache)
+ {
+ *cache = XZALLOC (struct jit_unwind_private);
+ priv_data = *cache;
+ priv_data->registers = XCALLOC (gdbarch_num_regs (target_gdbarch),
+ struct gdb_reg_value *);
+ priv_data->this_frame = this_frame;
+ }
+ else
+ {
+ priv_data = *cache;
+ priv_data->this_frame = this_frame;
+ }
+
+ callbacks.priv_data = priv_data;
+
+ /* Try to coax the provided unwinder to unwind the stack */
+ if (funcs->unwind (funcs, &callbacks) == GDB_SUCCESS)
+ {
+ if (jit_debug)
+ fprintf_unfiltered (gdb_stdlog, "Successfully unwound frame using "
+ "JIT reader.\n");
+ return 1;
+ }
+ if (jit_debug)
+ fprintf_unfiltered (gdb_stdlog, "Could not unwind frame using "
+ "JIT reader.\n");
+
+ xfree (priv_data->registers);
+ xfree (priv_data);
+ *cache = NULL;
+
+ return 0;
+}
+
+/* Also for the pseudo unwinder. */
+
+static enum unwind_stop_reason
+jit_frame_unwind_stop_reason (struct frame_info *this_frame, void **cache)
+{
+ return UNWIND_NO_REASON;
+}
+
+/* The frame_id function for the pseudo unwinder. Relays the call to
+ the loaded plugin. */
+
+static void
+jit_frame_this_id (struct frame_info *this_frame, void **cache,
+ struct frame_id *this_id)
+{
+ struct jit_unwind_private private;
+ struct gdb_frame_id frame_id;
+ struct gdb_reader_funcs *funcs;
+ struct gdb_unwind_callbacks callbacks;
+
+ private.registers = NULL;
+ private.this_frame = this_frame;
+
+ /* We don't expect the frame_id function to set any registers, so we
+ set reg_set to NULL. */
+ callbacks.reg_get = jit_unwind_reg_get_impl;
+ callbacks.reg_set = NULL;
+ callbacks.target_read = jit_target_read_impl;
+ callbacks.priv_data = &private;
+
+ gdb_assert (loaded_jit_reader);
+ funcs = loaded_jit_reader->functions;
+
+ frame_id = funcs->get_frame_id (funcs, &callbacks);
+ *this_id = frame_id_build (frame_id.stack_address, frame_id.code_address);
+}
+
+/* Pseudo unwinder function. Reads the previously fetched value for
+ the register from the cache. */
+
+static struct value *
+jit_frame_prev_register (struct frame_info *this_frame, void **cache, int reg)
+{
+ struct jit_unwind_private *priv = *cache;
+ struct gdb_reg_value *value;
+
+ if (priv == NULL)
+ return frame_unwind_got_optimized (this_frame, reg);
+
+ gdb_assert (priv->registers);
+ value = priv->registers[reg];
+ if (value && value->defined)
+ return frame_unwind_got_bytes (this_frame, reg, value->value);
+ else
+ return frame_unwind_got_optimized (this_frame, reg);
+}
+
+/* gdb_reg_value has a free function, which must be called on each
+ saved register value. */
+
+static void
+jit_dealloc_cache (struct frame_info *this_frame, void *cache)
+{
+ struct jit_unwind_private *priv_data = cache;
+ int i;
+
+ gdb_assert (priv_data->registers);
+
+ for (i = 0; i < gdbarch_num_regs (target_gdbarch); i++)
+ if (priv_data->registers[i] && priv_data->registers[i]->free)
+ priv_data->registers[i]->free (priv_data->registers[i]);
+
+ xfree (priv_data->registers);
+ xfree (priv_data);
+}
+
+/* Relay everything back to the unwinder registered by the JIT debug
+ info reader.*/
+
+static const struct frame_unwind jit_frame_unwind =
+{
+ NORMAL_FRAME,
+ jit_frame_unwind_stop_reason,
+ jit_frame_this_id,
+ jit_frame_prev_register,
+ NULL,
+ jit_frame_sniffer,
+ jit_dealloc_cache
+};
+
+
+/* This is the information that is stored at jit_gdbarch_data for each
+ architecture. */
+
+struct jit_gdbarch_data_type {
+
+ /* Has the (pseudo) unwinder been prepended? */
+
+ int unwinder_registered;
+};
+
+/* Check GDBARCH and prepend the pseudo JIT unwinder if needed. */
+
+static void
+jit_prepend_unwinder (struct gdbarch *gdbarch)
+{
+ struct jit_gdbarch_data_type *data;
+
+ data = gdbarch_data (gdbarch, jit_gdbarch_data);
+ if (!data->unwinder_registered)
+ {
+ frame_unwind_prepend_unwinder (gdbarch, &jit_frame_unwind);
+ data->unwinder_registered = 1;
+ }
+}
+
/* Register any already created translations. */

static void
@@ -920,6 +1165,8 @@ jit_inferior_init (struct gdbarch *gdbarch)
if (jit_debug)
fprintf_unfiltered (gdb_stdlog, "jit_inferior_init\n");

+ jit_prepend_unwinder (gdbarch);
+
inf_data = get_jit_inferior_data ();
if (jit_breakpoint_re_set_internal (gdbarch, inf_data) != 0)
return;
@@ -1082,6 +1329,18 @@ free_objfile_data (struct objfile *objfile, void *data)
xfree (data);
}

+/* Initialize the jit_gdbarch_data slot with an instance of struct
+ jit_gdbarch_data_type */
+
+static void *
+jit_gdbarch_data_init (struct obstack *obstack)
+{
+ struct jit_gdbarch_data_type *data =
+ obstack_alloc (obstack, sizeof (struct jit_gdbarch_data_type));
+ data->unwinder_registered = 0;
+ return data;
+}
+
/* Provide a prototype to silence -Wmissing-prototypes. */

extern void _initialize_jit (void);
@@ -1104,6 +1363,7 @@ _initialize_jit (void)
register_objfile_data_with_cleanup (NULL,free_objfile_data);
jit_inferior_data =
register_inferior_data_with_cleanup (jit_inferior_data_cleanup);
+ jit_gdbarch_data = gdbarch_data_register_pre_init (jit_gdbarch_data_init);
add_com ("load-jit-reader", no_class, load_jit_reader_command, _("\
Try to load file FILE as a debug info reader (and unwinder) for\n\
JIT compiled code from " LIBDIR "/gdb\n\
--
1.7.5.4