gdb: fix selecting tail-call frames by name
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Commit Message
I noticed that attempting to select a tail-call frame using 'frame
function NAME' wouldn't work:
(gdb) bt
#0 func_that_never_returns () at /tmp/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/frame-selection.c:49
#1 0x0000000000401183 in func_that_tail_calls () at /tmp/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/frame-selection.c:59
#2 0x00000000004011a5 in main () at /tmp/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/frame-selection.c:70
(gdb) frame function func_that_tail_calls
No frame for function "func_that_tail_calls".
(gdb) up
#1 0x0000000000401183 in func_that_tail_calls () at /tmp/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/frame-selection.c:59
59 func_that_never_returns ();
(gdb) disassemble
Dump of assembler code for function func_that_tail_calls:
0x000000000040117a <+0>: push %rbp
0x000000000040117b <+1>: mov %rsp,%rbp
0x000000000040117e <+4>: call 0x40116c <func_that_never_returns>
End of assembler dump.
(gdb)
The problem is that the 'function' mechanism uses get_frame_pc() and
then compares the address returned with the bounds of the function
we're looking for.
So in this case, the bounds of func_that_tail_calls are 0x40117a to
0x401183, with 0x401183 being the first address _after_ the function.
However, because func_that_tail_calls ends in a tail call, then the
get_frame_pc() is 0x401183, the first address after the function. As
a result, GDB fails to realise that frame #1 is inside the function
we're looking for, and the lookup fails.
The fix is to use get_frame_address_in_block, which will return an
adjusted address, in this case, 0x401182, which is within the function
bounds. Now the lookup works:
(gdb) frame function func_that_tail_calls
#1 0x0000000000401183 in func_that_tail_calls () at /tmp/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/frame-selection.c:59
59 func_that_never_returns ();
(gdb)
I've extended the gdb.base/frame-selection.exp test to cover this
case.
---
gdb/stack.c | 6 ++--
gdb/testsuite/gdb.base/frame-selection.c | 21 ++++++++++++
gdb/testsuite/gdb.base/frame-selection.exp | 37 ++++++++++++++++++++++
3 files changed, 62 insertions(+), 2 deletions(-)
base-commit: ac8f3fc9330da0302ebb491bf2bac8da5e035e35
Comments
Andrew Burgess <aburgess@redhat.com> writes:
> I noticed that attempting to select a tail-call frame using 'frame
> function NAME' wouldn't work:
>
> (gdb) bt
> #0 func_that_never_returns () at /tmp/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/frame-selection.c:49
> #1 0x0000000000401183 in func_that_tail_calls () at /tmp/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/frame-selection.c:59
> #2 0x00000000004011a5 in main () at /tmp/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/frame-selection.c:70
> (gdb) frame function func_that_tail_calls
> No frame for function "func_that_tail_calls".
> (gdb) up
> #1 0x0000000000401183 in func_that_tail_calls () at /tmp/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/frame-selection.c:59
> 59 func_that_never_returns ();
> (gdb) disassemble
> Dump of assembler code for function func_that_tail_calls:
> 0x000000000040117a <+0>: push %rbp
> 0x000000000040117b <+1>: mov %rsp,%rbp
> 0x000000000040117e <+4>: call 0x40116c <func_that_never_returns>
> End of assembler dump.
> (gdb)
>
> The problem is that the 'function' mechanism uses get_frame_pc() and
> then compares the address returned with the bounds of the function
> we're looking for.
>
> So in this case, the bounds of func_that_tail_calls are 0x40117a to
> 0x401183, with 0x401183 being the first address _after_ the function.
>
> However, because func_that_tail_calls ends in a tail call, then the
> get_frame_pc() is 0x401183, the first address after the function. As
> a result, GDB fails to realise that frame #1 is inside the function
> we're looking for, and the lookup fails.
>
> The fix is to use get_frame_address_in_block, which will return an
> adjusted address, in this case, 0x401182, which is within the function
> bounds. Now the lookup works:
>
> (gdb) frame function func_that_tail_calls
> #1 0x0000000000401183 in func_that_tail_calls () at /tmp/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.base/frame-selection.c:59
> 59 func_that_never_returns ();
> (gdb)
>
> I've extended the gdb.base/frame-selection.exp test to cover this
> case.
I've checked this in.
Thanks,
Andrew
@@ -2863,9 +2863,11 @@ find_frame_for_function (const char *function_name)
do
{
+ CORE_ADDR frame_pc = get_frame_address_in_block (frame);
+
for (size_t i = 0; (i < sals.size () && !found); i++)
- found = (get_frame_pc (frame) >= func_bounds[i].low
- && get_frame_pc (frame) < func_bounds[i].high);
+ found = (frame_pc >= func_bounds[i].low
+ && frame_pc < func_bounds[i].high);
if (!found)
{
level = 1;
@@ -15,6 +15,8 @@
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
+#include <stdlib.h>
+
int
frame_2 (void)
{
@@ -40,6 +42,23 @@ recursive (int arg)
return v;
}
+/* A function that never returns. */
+void __attribute__((noreturn))
+func_that_never_returns (void)
+{
+ exit (0);
+}
+
+/* A function that tail calls. Calling a 'noreturn' function isn't
+ required for a tail call, but at low optimisation levels, gcc will apply
+ the tail call optimisation only for 'noreturn' calls. */
+
+void
+func_that_tail_calls (void)
+{
+ func_that_never_returns ();
+}
+
int
main (void)
{
@@ -48,5 +67,7 @@ main (void)
i = frame_1 ();
j = recursive (0);
+ func_that_tail_calls ();
+
return i + j;
}
@@ -186,3 +186,40 @@ with_test_prefix "second frame_2 breakpoint" {
gdb_test "frame function recursive" "#1 $hex in recursive.*" \
"select frame for function recursive, third attempt"
}
+
+# At one point using the 'function' sub-command (e.g. 'frame function
+# ...') would fail to select a frame if the frame ended with a
+# tail-call, and the address within the frame was outside the bounds
+# of the function.
+with_test_prefix "stack with tail call" {
+ gdb_breakpoint func_that_never_returns
+ gdb_continue_to_breakpoint func_that_never_returns
+
+ gdb_test "bt" \
+ [multi_line \
+ "#0 func_that_never_returns \\(\\) at \[^\r\n\]+" \
+ "#1 $hex in func_that_tail_calls \\(\\) at \[^\r\n\]+" \
+ "#2 $hex in main \\(\\) at \[^\r\n\]+"] \
+ "bt from func_that_never_returns"
+
+ # Reset the frame addresses based on the new stack.
+ gdb_test "frame 0" "#0 func_that_never_returns.*"
+ set frame_0_address [ get_frame_address "frame 0" ]
+ gdb_test "frame 1" "#1 $hex in func_that_tail_calls.*"
+ set frame_1_address [ get_frame_address "frame 1" ]
+ gdb_test "frame 2" "#2 $hex in main.*"
+ set frame_2_address [ get_frame_address "frame 2" ]
+
+ # Test 'select-frame function ...' command.
+ gdb_test_no_output "select-frame function func_that_never_returns"
+ check_frame "0" "${frame_0_address}" "func_that_never_returns"
+ gdb_test_no_output "select-frame function func_that_tail_calls"
+ check_frame "1" "${frame_1_address}" "func_that_tail_calls"
+ gdb_test_no_output "select-frame function main"
+ check_frame "2" "${frame_2_address}" "main"
+
+ # Test 'frame function ...' command.
+ gdb_test "frame function func_that_never_returns" "#0 func_that_never_returns.*"
+ gdb_test "frame function func_that_tail_calls" "#1 $hex in func_that_tail_calls.*"
+ gdb_test "frame function main" "#2 $hex in main.*"
+}