[PATCH] "tfind" across unavailable-stack frames.

Pedro Alves
2013-12-13T17:49:48Z

As discussed in the sub-thread starting at:

https://sourceware.org/ml/gdb-patches/2013-12/msg00528.html

I've cleaned up this patch, and adjusted the testsuite.

The original was here:

https://sourceware.org/ml/gdb-patches/2013-04/msg00541.html

In this version, I made the unwind->this_id() be responsible
for using frame_id_build_unavailable_stack instead. That
allows the unwinder using perhaps a more detailed frame_id
(it sounds like record-btrace will want that.), and allows
avoiding get_frame_func when the might not be available.

Comments?

-------------
"tfind" across unavailable-stack frames.

Like when stepping, the current stack frame location is expected to be
printed as result of tfind command, if that results in moving to a
different function. In tfind_1 we see:

if (from_tty
&& (has_stack_frames () || traceframe_number >= 0))
{
enum print_what print_what;

/* NOTE: in imitation of the step command, try to determine
whether we have made a transition from one function to
another. If so, we'll print the "stack frame" (ie. the new
function and it's arguments) -- otherwise we'll just show the
new source line. */

if (frame_id_eq (old_frame_id,
get_frame_id (get_current_frame ())))
print_what = SRC_LINE;
else
print_what = SRC_AND_LOC;

print_stack_frame (get_selected_frame (NULL), 1, print_what, 1);
do_displays ();
}

However, when we haven't collected any registers in the tracepoint
(collect $regs), that doesn't actually work:

(gdb) tstart
(gdb) info tracepoints
Num Type Disp Enb Address What
1 tracepoint keep y 0x080483b7 in func0
at ../.././../git/gdb/testsuite/gdb.trace/circ.c:28
collect testload
installed on target
2 tracepoint keep y 0x080483bc in func1
at ../.././../git/gdb/testsuite/gdb.trace/circ.c:32
collect testload
installed on target
(gdb) c
Continuing.

Breakpoint 3, end () at ../.././../git/gdb/testsuite/gdb.trace/circ.c:72
72 }
(gdb) tstop
(gdb) tfind start
Found trace frame 0, tracepoint 1
#0 func0 () at ../.././../git/gdb/testsuite/gdb.trace/circ.c:28
28 }
(gdb) tfind
Found trace frame 1, tracepoint 2
32 }
(gdb)

When we don't have info about the stack available
(UNWIND_UNAVAILABLE), frames end up with outer_frame_id as frame ID.
And in the scenario above, the issue is that both frames before and
after the second tfind (the frames for func0 an func1) have the same
id (outer_frame_id), so the frame_id_eq check returns false, even
though the frames were of different functions. GDB knows that,
because the PC is inferred from the tracepoint's address, even if no
registers were collected.

To fix this, this patch adds support for frame ids with a valid code
address, but <unavailable> stack address, and then makes the unwinders
use that instead of the catch-all outer_frame_id for such frames. The
frame_id_eq check in tfind_1 then automatically does the right thing
as expected.

I tested with --directory=gdb.trace/ , before/after the patch, and
compared the resulting gdb.logs, then adjusted the tests to expect the
extra output that came out. Turns out that was only circ.exp, the
original test that actually brought this issue to light.

Tested on x86_64 Fedora 17, native and gdbserver.

gdb/
2013-12-13 Pedro Alves <palves@redhat.com>

* frame.h (enum frame_id_stack_status): New enum.
(struct frame_id) <stack_addr>: Adjust comment.
<stack_addr_p>: Delete field, replaced with ...
<stack_status>: ... this new field.
(frame_id_build_unavailable_stack): Declare.
* frame.c (frame_addr_hash, fprint_field, outer_frame_id)
(frame_id_build_special): Adjust.
(frame_id_build_unavailable_stack): New function.
(frame_id_build, frame_id_build_wild): Adjust.
(frame_id_p, frame_id_eq, frame_id_inner): Adjust to take into
account frames with unavailable stack.

* amd64-tdep.c (amd64_frame_this_id)
(amd64_sigtramp_frame_this_id, amd64_epilogue_frame_this_id): Use
frame_id_build_unavailable_stack.
* dwarf2-frame.c (dwarf2_frame_this_id): Likewise.
* i386-tdep.c (i386_frame_this_id, i386_epilogue_frame_this_id)
(i386_sigtramp_frame_this_id): Likewise.

gdb/testsuite/
2013-12-13 Pedro Alves <palves@redhat.com>

* gdb.trace/circ.exp: Expect frame info to be printed when
switching between frames with unavailable stack, but different
functions.
---
gdb/amd64-tdep.c | 32 ++++++++++++++----------
gdb/dwarf2-frame.c | 9 +++----
gdb/frame.c | 54 +++++++++++++++++++++++++++++-----------
gdb/frame.h | 30 +++++++++++++++++++---
gdb/i386-tdep.c | 33 ++++++++++++++----------
gdb/testsuite/gdb.trace/circ.exp | 4 +--
6 files changed, 112 insertions(+), 50 deletions(-)

diff --git a/gdb/amd64-tdep.c b/gdb/amd64-tdep.c
index 19968fc..d0dc587 100644
--- a/gdb/amd64-tdep.c
+++ b/gdb/amd64-tdep.c
@@ -2378,13 +2378,14 @@ amd64_frame_this_id (struct frame_info *this_frame, void **this_cache,
amd64_frame_cache (this_frame, this_cache);

if (!cache->base_p)
- return;
-
- /* This marks the outermost frame. */
- if (cache->base == 0)
- return;
-
- (*this_id) = frame_id_build (cache->base + 16, cache->pc);
+ (*this_id) = frame_id_build_unavailable_stack (cache->pc);
+ else if (cache->base == 0)
+ {
+ /* This marks the outermost frame. */
+ return;
+ }
+ else
+ (*this_id) = frame_id_build (cache->base + 16, cache->pc);
}

static struct value *
@@ -2499,9 +2500,14 @@ amd64_sigtramp_frame_this_id (struct frame_info *this_frame,
amd64_sigtramp_frame_cache (this_frame, this_cache);

if (!cache->base_p)
- return;
-
- (*this_id) = frame_id_build (cache->base + 16, get_frame_pc (this_frame));
+ (*this_id) = frame_id_build_unavailable_stack (get_frame_pc (this_frame));
+ else if (cache->base == 0)
+ {
+ /* This marks the outermost frame. */
+ return;
+ }
+ else
+ (*this_id) = frame_id_build (cache->base + 16, get_frame_pc (this_frame));
}

static struct value *
@@ -2670,9 +2676,9 @@ amd64_epilogue_frame_this_id (struct frame_info *this_frame,
this_cache);

if (!cache->base_p)
- return;
-
- (*this_id) = frame_id_build (cache->base + 8, cache->pc);
+ (*this_id) = frame_id_build_unavailable_stack (cache->pc);
+ else
+ (*this_id) = frame_id_build (cache->base + 8, cache->pc);
}

static const struct frame_unwind amd64_epilogue_frame_unwind =
diff --git a/gdb/dwarf2-frame.c b/gdb/dwarf2-frame.c
index c4f8771..91b2120 100644
--- a/gdb/dwarf2-frame.c
+++ b/gdb/dwarf2-frame.c
@@ -1275,12 +1275,11 @@ dwarf2_frame_this_id (struct frame_info *this_frame, void **this_cache,
dwarf2_frame_cache (this_frame, this_cache);

if (cache->unavailable_retaddr)
+ (*this_id) = frame_id_build_unavailable_stack (get_frame_func (this_frame));
+ else if (cache->undefined_retaddr)
return;
-
- if (cache->undefined_retaddr)
- return;
-
- (*this_id) = frame_id_build (cache->cfa, get_frame_func (this_frame));
+ else
+ (*this_id) = frame_id_build (cache->cfa, get_frame_func (this_frame));
}

static struct value *
diff --git a/gdb/frame.c b/gdb/frame.c
index 6a8b5ae..ed31c9e 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -166,10 +166,11 @@ frame_addr_hash (const void *ap)
const struct frame_id f_id = frame->this_id.value;
hashval_t hash = 0;

- gdb_assert (f_id.stack_addr_p || f_id.code_addr_p
+ gdb_assert (f_id.stack_status != FID_STACK_INVALID
+ || f_id.code_addr_p
|| f_id.special_addr_p);

- if (f_id.stack_addr_p)
+ if (f_id.stack_status == FID_STACK_VALID)
hash = iterative_hash (&f_id.stack_addr,
sizeof (f_id.stack_addr), hash);
if (f_id.code_addr_p)
@@ -317,13 +318,23 @@ void
fprint_frame_id (struct ui_file *file, struct frame_id id)
{
fprintf_unfiltered (file, "{");
- fprint_field (file, "stack", id.stack_addr_p, id.stack_addr);
+
+ if (id.stack_status == FID_STACK_INVALID)
+ fprintf_unfiltered (file, "!stack");
+ else if (id.stack_status == FID_STACK_UNAVAILABLE)
+ fprintf_unfiltered (file, "stack=<unavailable>");
+ else
+ fprintf_unfiltered (file, "stack=%s", hex_string (id.stack_addr));
fprintf_unfiltered (file, ",");
+
fprint_field (file, "code", id.code_addr_p, id.code_addr);
fprintf_unfiltered (file, ",");
+
fprint_field (file, "special", id.special_addr_p, id.special_addr);
+
if (id.artificial_depth)
fprintf_unfiltered (file, ",artificial=%d", id.artificial_depth);
+
fprintf_unfiltered (file, "}");
}

@@ -487,7 +498,7 @@ frame_unwind_caller_id (struct frame_info *next_frame)
}

const struct frame_id null_frame_id; /* All zeros. */
-const struct frame_id outer_frame_id = { 0, 0, 0, 0, 0, 1, 0 };
+const struct frame_id outer_frame_id = { 0, 0, 0, FID_STACK_INVALID, 0, 1, 0 };

struct frame_id
frame_id_build_special (CORE_ADDR stack_addr, CORE_ADDR code_addr,
@@ -496,7 +507,7 @@ frame_id_build_special (CORE_ADDR stack_addr, CORE_ADDR code_addr,
struct frame_id id = null_frame_id;

id.stack_addr = stack_addr;
- id.stack_addr_p = 1;
+ id.stack_status = FID_STACK_VALID;
id.code_addr = code_addr;
id.code_addr_p = 1;
id.special_addr = special_addr;
@@ -504,13 +515,26 @@ frame_id_build_special (CORE_ADDR stack_addr, CORE_ADDR code_addr,
return id;
}

+/* See frame.h. */
+
+struct frame_id
+frame_id_build_unavailable_stack (CORE_ADDR code_addr)
+{
+ struct frame_id id = null_frame_id;
+
+ id.stack_status = FID_STACK_UNAVAILABLE;
+ id.code_addr = code_addr;
+ id.code_addr_p = 1;
+ return id;
+}
+
struct frame_id
frame_id_build (CORE_ADDR stack_addr, CORE_ADDR code_addr)
{
struct frame_id id = null_frame_id;

id.stack_addr = stack_addr;
- id.stack_addr_p = 1;
+ id.stack_status = FID_STACK_VALID;
id.code_addr = code_addr;
id.code_addr_p = 1;
return id;
@@ -522,7 +546,7 @@ frame_id_build_wild (CORE_ADDR stack_addr)
struct frame_id id = null_frame_id;

id.stack_addr = stack_addr;
- id.stack_addr_p = 1;
+ id.stack_status = FID_STACK_VALID;
return id;
}

@@ -532,7 +556,7 @@ frame_id_p (struct frame_id l)
int p;

/* The frame is valid iff it has a valid stack address. */
- p = l.stack_addr_p;
+ p = l.stack_status != FID_STACK_INVALID;
/* outer_frame_id is also valid. */
if (!p && memcmp (&l, &outer_frame_id, sizeof (l)) == 0)
p = 1;
@@ -559,19 +583,20 @@ frame_id_eq (struct frame_id l, struct frame_id r)
{
int eq;

- if (!l.stack_addr_p && l.special_addr_p
- && !r.stack_addr_p && r.special_addr_p)
+ if (l.stack_status == FID_STACK_INVALID && l.special_addr_p
+ && r.stack_status == FID_STACK_INVALID && r.special_addr_p)
/* The outermost frame marker is equal to itself. This is the
dodgy thing about outer_frame_id, since between execution steps
we might step into another function - from which we can't
unwind either. More thought required to get rid of
outer_frame_id. */
eq = 1;
- else if (!l.stack_addr_p || !r.stack_addr_p)
+ else if (l.stack_status == FID_STACK_INVALID
+ || l.stack_status == FID_STACK_INVALID)
/* Like a NaN, if either ID is invalid, the result is false.
Note that a frame ID is invalid iff it is the null frame ID. */
eq = 0;
- else if (l.stack_addr != r.stack_addr)
+ else if (l.stack_status != r.stack_status || l.stack_addr != r.stack_addr)
/* If .stack addresses are different, the frames are different. */
eq = 0;
else if (l.code_addr_p && r.code_addr_p && l.code_addr != r.code_addr)
@@ -638,8 +663,9 @@ frame_id_inner (struct gdbarch *gdbarch, struct frame_id l, struct frame_id r)
{
int inner;

- if (!l.stack_addr_p || !r.stack_addr_p)
- /* Like NaN, any operation involving an invalid ID always fails. */
+ if (l.stack_status != FID_STACK_VALID || r.stack_status != FID_STACK_VALID)
+ /* Like NaN, any operation involving an invalid ID always fails.
+ Likewise if either ID has an unavailable stack address. */
inner = 0;
else if (l.artificial_depth > r.artificial_depth
&& l.stack_addr == r.stack_addr
diff --git a/gdb/frame.h b/gdb/frame.h
index f8d5bc1..8f6429a 100644
--- a/gdb/frame.h
+++ b/gdb/frame.h
@@ -76,6 +76,24 @@ struct block;
struct gdbarch;
struct ui_file;

+/* Status of a given frame's stack. */
+
+enum frame_id_stack_status
+{
+ /* Stack address is invalid. E.g., This frame is the outermost
+ (i.e., _start), and the stack hasn't been setup yet. */
+ FID_STACK_INVALID = 0,
+
+ /* Stack address is valid, and the address is found in the
+ corresponding ..._addr field. */
+ FID_STACK_VALID = 1,
+
+ /* Stack address is unavailable. I.e., there's a valid stack, but
+ we don't know where it is (because memory or registers we'd
+ compute it from were not collected). */
+ FID_STACK_UNAVAILABLE = -1
+};
+
/* The frame object. */

struct frame_info;
@@ -97,8 +115,8 @@ struct frame_id
function pointer register or stack pointer register. They are
wrong.

- This field is valid only if stack_addr_p is true. Otherwise, this
- frame represents the null frame. */
+ This field is valid only if frame_id.stack_status is
+ FID_STACK_VALID. */
CORE_ADDR stack_addr;

/* The frame's code address. This shall be constant through out the
@@ -129,7 +147,7 @@ struct frame_id
CORE_ADDR special_addr;

/* Flags to indicate the above fields have valid contents. */
- unsigned int stack_addr_p : 1;
+ ENUM_BITFIELD(frame_id_stack_status) stack_status : 2;
unsigned int code_addr_p : 1;
unsigned int special_addr_p : 1;

@@ -169,6 +187,12 @@ extern struct frame_id frame_id_build_special (CORE_ADDR stack_addr,
CORE_ADDR code_addr,
CORE_ADDR special_addr);

+/* Construct a frame ID representing a frame where the stack address
+ exists, but is unavailable. The first parameter is the frame's
+ constant code address (typically the entry point). The special
+ identifier address is set to indicate a wild card. */
+extern struct frame_id frame_id_build_unavailable_stack (CORE_ADDR code_addr);
+
/* Construct a wild card frame ID. The parameter is the frame's constant
stack address (typically the outer-bound). The code address as well
as the special identifier address are set to indicate wild cards. */
diff --git a/gdb/i386-tdep.c b/gdb/i386-tdep.c
index a1a4453..5b4a5a3 100644
--- a/gdb/i386-tdep.c
+++ b/gdb/i386-tdep.c
@@ -1905,12 +1905,17 @@ i386_frame_this_id (struct frame_info *this_frame, void **this_cache,
{
struct i386_frame_cache *cache = i386_frame_cache (this_frame, this_cache);

- /* This marks the outermost frame. */
- if (cache->base == 0)
- return;
-
- /* See the end of i386_push_dummy_call. */
- (*this_id) = frame_id_build (cache->base + 8, cache->pc);
+ if (!cache->base_p)
+ (*this_id) = frame_id_build_unavailable_stack (cache->pc);
+ else if (cache->base == 0)
+ {
+ /* This marks the outermost frame. */
+ }
+ else
+ {
+ /* See the end of i386_push_dummy_call. */
+ (*this_id) = frame_id_build (cache->base + 8, cache->pc);
+ }
}

static enum unwind_stop_reason
@@ -2091,9 +2096,9 @@ i386_epilogue_frame_this_id (struct frame_info *this_frame,
i386_epilogue_frame_cache (this_frame, this_cache);

if (!cache->base_p)
- return;
-
- (*this_id) = frame_id_build (cache->base + 8, cache->pc);
+ (*this_id) = frame_id_build_unavailable_stack (cache->pc);
+ else
+ (*this_id) = frame_id_build (cache->base + 8, cache->pc);
}

static struct value *
@@ -2284,10 +2289,12 @@ i386_sigtramp_frame_this_id (struct frame_info *this_frame, void **this_cache,
i386_sigtramp_frame_cache (this_frame, this_cache);

if (!cache->base_p)
- return;
-
- /* See the end of i386_push_dummy_call. */
- (*this_id) = frame_id_build (cache->base + 8, get_frame_pc (this_frame));
+ (*this_id) = frame_id_build_unavailable_stack (get_frame_pc (this_frame));
+ else
+ {
+ /* See the end of i386_push_dummy_call. */
+ (*this_id) = frame_id_build (cache->base + 8, get_frame_pc (this_frame));
+ }
}

static struct value *
diff --git a/gdb/testsuite/gdb.trace/circ.exp b/gdb/testsuite/gdb.trace/circ.exp
index f605bb6..6246e35 100644
--- a/gdb/testsuite/gdb.trace/circ.exp
+++ b/gdb/testsuite/gdb.trace/circ.exp
@@ -221,7 +221,7 @@ with_test_prefix "normal buffer" {
"first frame is at func0"

gdb_test "tfind pc func9" \
- ".*Found trace frame $decimal, tracepoint $decimal.*" \
+ ".*Found trace frame $decimal, tracepoint $decimal\r\n#0 func9 .*" \
"find frame for func9"
}

@@ -282,6 +282,6 @@ with_test_prefix "circular buffer" {

gdb_test \
"tfind pc func9" \
- ".*Found trace frame $decimal, tracepoint $decimal.*" \
+ ".*Found trace frame $decimal, tracepoint $decimal\r\n#0 func9 .*" \
"find frame for func9"
}
--
1.7.11.7