[PATCH 2/2 ] PowerPC: fix for gdb.reverse/finish-precsave.exp and gdb.reverse/finish-reverse.exp

Carl Love via Gdb-patches
2023-03-01T21:00:29Z

Tom, Ulrich, Bruno, Pedro, GDB maintainers:

This patch fixes the reverse-finish command on PowerPC. The command
now works the same as on other architectures, specifically X86. There
are no functional changes for other architectures. The patch includes
a new testcase to verify the reverse-finish command works correctly
with the multiple entry points supported by PowerPC.

Patch tested on PowerPC and 5th generation X86 with no regression
failures.

Carl

--------------------------------------------------------
PowerPC: fix for gdb.reverse/finish-precsave.exp and gdb.reverse/finish-reverse.exp

PPC64 multiple entry points, a normal entry point and an alternate entry
point. The alternate entry point is to setup the Table of Contents (TOC)
register before continuing at the normal entry point. When the TOC is
already valid, the normal entry point is used, this is typically the case.
The alternate entry point is typically referred to as the global entry
point (GEP) in IBM. The normal entry point is typically referred to as
the local entry point (LEP).

When GDB is executing the finish command in reverse, the function
finish_backward currently sets the break point at the alternate entry point.
This issue is if the function, when executing in the forward direction, entered
the function via the normal entry point, execution in the reverse direction
will never sees the break point at the alternate entry point. In this case,
the reverse execution continues until the next break point is encountered thus
stopping at the wrong place.

This patch adds a new address to struct execution_control_state to hold the
address of the alternate entry point (GEP). The finish_backwards function
is updated, if the stopping point is between the normal entry point (LEP)
and the end of the function, a breakpoint is set at the normal entry point.
If the stopping point is between the entry points, a breakpoint is set at
the alternate entry point. This ensures that GDB will always stop at the
normal entry point. If the function did enter via the alternate entry point,
GDB will detect that and continue to execute backwards in the function until
the alternate entry point is reached.

The patch fixes the behavior of the reverse-finish command on PowerPC to
match the behavior of the command on other platforms, specifically X86.
The patch does not change the behavior of the command on X86.

A new test is added to verify the reverse-finish command on PowerPC
correctly stops at the instruction where the function call is made.

The patch fixes 11 regression errors in test gdb.reverse/finish-precsave.exp
and 11 regression errors in test gdb.reverse/finish-reverse.exp.

The patch has been tested on Power 10 and X86 processor with no new
regression failures.
---
gdb/infcmd.c | 47 ++--
gdb/infrun.c | 24 ++
.../gdb.reverse/finish-reverse-next.c | 91 +++++++
.../gdb.reverse/finish-reverse-next.exp | 224 ++++++++++++++++++
4 files changed, 369 insertions(+), 17 deletions(-)
create mode 100644 gdb/testsuite/gdb.reverse/finish-reverse-next.c
create mode 100644 gdb/testsuite/gdb.reverse/finish-reverse-next.exp

diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index c369b795757..81c617448af 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -1728,28 +1728,41 @@ finish_backward (struct finish_command_fsm *sm)
no way that a function up the stack can have a return address
that's equal to its entry point. */

- if (sal.pc != pc)
- {
- frame_info_ptr frame = get_selected_frame (nullptr);
- struct gdbarch *gdbarch = get_frame_arch (frame);
+ CORE_ADDR alt_entry_point = sal.pc;
+ CORE_ADDR entry_point = alt_entry_point;
+ frame_info_ptr frame = get_selected_frame (nullptr);
+ struct gdbarch *gdbarch = get_frame_arch (frame);
+
+ if (gdbarch_skip_entrypoint_p (gdbarch))
+ /* Some architectures, like PowerPC use local and global entry points.
+ There is only one Entry Point (GEP = LEP) for other architectures.
+ The GEP is an alternate entry point. The LEP is the normal entry point.
+ The value of entry_point was initialized to the alternate entry point
+ (GEP). It will be adjusted to the normal entry point if the function
+ has two entry points. */
+ entry_point = gdbarch_skip_entrypoint (gdbarch, sal.pc);

- /* Set a step-resume at the function's entry point. Once that's
- hit, we'll do one more step backwards. */
+ if ((pc < alt_entry_point) || (pc > entry_point))
+ {
+ /* We are in the body of the function. Set a breakpoint to go back to
+ the normal entry point. */
symtab_and_line sr_sal;
- sr_sal.pc = sal.pc;
+ sr_sal.pc = entry_point;
sr_sal.pspace = get_frame_program_space (frame);
- insert_step_resume_breakpoint_at_sal (gdbarch,
- sr_sal, null_frame_id);
-
- proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
+ insert_step_resume_breakpoint_at_sal (gdbarch, sr_sal,
+ null_frame_id);
}
+
else
- {
- /* We're almost there -- we just need to back up by one more
- single-step. */
- tp->control.step_range_start = tp->control.step_range_end = 1;
- proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
- }
+ /* We are either at one of the entry points or between the entry points.
+ If we are not at the alt_entry point, go back to the alt_entry_point
+ If we at the normal entry point step back one instruction, when we
+ stop we will determine if we entered via the entry point or the
+ alternate entry point. If we are at the alternate entry point,
+ single step back to the function call. */
+ tp->control.step_range_start = tp->control.step_range_end = 1;
+
+ proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
}

/* finish_forward -- helper function for finish_command. FRAME is the
diff --git a/gdb/infrun.c b/gdb/infrun.c
index ab77300f1ff..ca2fc02898a 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1938,6 +1938,7 @@ struct execution_control_state

struct target_waitstatus ws;
int stop_func_filled_in = 0;
+ CORE_ADDR stop_func_alt_start = 0;
CORE_ADDR stop_func_start = 0;
CORE_ADDR stop_func_end = 0;
const char *stop_func_name = nullptr;
@@ -4822,6 +4823,11 @@ fill_in_stop_func (struct gdbarch *gdbarch,
ecs->stop_func_start
+= gdbarch_deprecated_function_start_offset (gdbarch);

+ /* PowerPC functions have a Local Entry Point (LEP) and a Global
+ Entry Point (GEP). There is only one Entry Point (GEP = LEP) for
+ other architectures. */
+ ecs->stop_func_alt_start = ecs->stop_func_start;
+
if (gdbarch_skip_entrypoint_p (gdbarch))
ecs->stop_func_start
= gdbarch_skip_entrypoint (gdbarch, ecs->stop_func_start);
@@ -7411,6 +7417,24 @@ process_event_stop_test (struct execution_control_state *ecs)
}
}

+ if (execution_direction == EXEC_REVERSE
+ && ecs->event_thread->control.proceed_to_finish
+ && ecs->event_thread->stop_pc () >= ecs->stop_func_alt_start
+ && ecs->event_thread->stop_pc () < ecs->stop_func_start)
+ {
+ /* We are executing the reverse-finish command.
+ If the system supports multiple entry points and we are finishing a
+ function in reverse. If we are between the entry points singe-step
+ back to the alternate entry point. If we are at the alternate entry
+ point -- just need to back up by one more single-step, which
+ should take us back to the function call. */
+ ecs->event_thread->control.step_range_start
+ = ecs->event_thread->control.step_range_end = 1;
+ keep_going (ecs);
+ return;
+
+ }
+
if (ecs->event_thread->control.step_range_end == 1)
{
/* It is stepi or nexti. We always want to stop stepping after
diff --git a/gdb/testsuite/gdb.reverse/finish-reverse-next.c b/gdb/testsuite/gdb.reverse/finish-reverse-next.c
new file mode 100644
index 00000000000..e95ee8e33a6
--- /dev/null
+++ b/gdb/testsuite/gdb.reverse/finish-reverse-next.c
@@ -0,0 +1,91 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2012-2023 Free Software Foundation, Inc.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+/* The reverse finish command should return from a function and stop on
+ the first instruction of the source line where the function call is made.
+ Specifically, the behavior should match doing a reverse next from the
+ first instruction in the function. GDB should only require one reverse
+ step or next statement to reach the previous source code line.
+
+ This test verifies the fix for gdb bugzilla:
+
+ https://sourceware.org/bugzilla/show_bug.cgi?id=29927
+
+ PowerPC supports two entry points to a function. The normal entry point
+ is called the local entry point (LEP). The alternate entry point is called
+ the global entry point (GEP). The GEP is only used if the table of
+ contents (TOC) value stored in register r2 needs to be setup prior to
+ execution starting at the LEP. A function call via a function pointer
+ will entry via the GEP. A normal function call will enter via the LEP.
+
+ This test has been expanded to include tests to verify the reverse-finish
+ command works properly if the function is called via the GEP. The original
+ test only verified the reverse-finish command for a normal call that used
+ the LEP. */
+
+int
+function2 (int a, int b)
+{
+ int ret = 0;
+ ret = ret + a + b;
+ return ret;
+}
+
+int
+function1 (int a, int b) // FUNCTION1
+{
+ int ret = 0;
+ int (*funp) (int, int) = &function2;
+ /* The assembly code for this function when compiled for PowerPC is as
+ follows:
+
+ 0000000010000758 <function1>:
+ 10000758: 02 10 40 3c lis r2,4098 <- GEP
+ 1000075c: 00 7f 42 38 addi r2,r2,32512
+ 10000760: a6 02 08 7c mflr r0 <- LEP
+ 10000764: 10 00 01 f8 std r0,16(r1)
+ ....
+
+ When the function is called on PowerPC with function1 (a, b) the call
+ enters at the Local Entry Point (LEP). When the function is called via
+ a function pointer, the Global Entry Point (GEP) for function1 is used.
+ The GEP sets up register 2 before reaching the LEP.
+ */
+ ret = funp (a + 1, b + 2);
+ return ret;
+}
+
+int
+main(int argc, char* argv[])
+{
+ int a, b;
+ int (*funp) (int, int) = &function1;
+
+ /* Call function via Local Entry Point (LEP). */
+
+ a = 1;
+ b = 5;
+
+ function1 (a, b); // CALL VIA LEP
+
+ /* Call function via Global Entry Point (GEP). */
+ a = 10;
+ b = 50;
+
+ funp (a, b); // CALL VIA GEP
+ return 0;
+}
diff --git a/gdb/testsuite/gdb.reverse/finish-reverse-next.exp b/gdb/testsuite/gdb.reverse/finish-reverse-next.exp
new file mode 100644
index 00000000000..1f53b649a7d
--- /dev/null
+++ b/gdb/testsuite/gdb.reverse/finish-reverse-next.exp
@@ -0,0 +1,224 @@
+# Copyright 2008-2023 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+# This file is part of the GDB testsuite. It tests reverse stepping.
+# Lots of code borrowed from "step-test.exp".
+
+# The reverse finish command should return from a function and stop on
+# the first instruction of the source line where the function call is made.
+# Specifically, the behavior should match doing a reverse next from the
+# first instruction in the function. GDB should only take one reverse step
+# or next statement to reach the previous source code line.
+
+# This testcase verifies the reverse-finish command stops at the first
+# instruction in the source code line where the function was called. There
+# are two scenarios that must be checked:
+# 1) gdb is at the entry point instruction for the function
+# 2) gdb is in the body of the function.
+
+# This test verifies the fix for gdb bugzilla:
+# https://sourceware.org/bugzilla/show_bug.cgi?id=29927
+
+# PowerPC supports two entry points to a function. The normal entry point
+# is called the local entry point (LEP). The alternate entry point is called
+# the global entry point (GEP). A function call via a function pointer
+# will entry via the GEP. A normal function call will enter via the LEP.
+#
+# This test has been expanded to include tests to verify the reverse-finish
+# command works properly if the function is called via the GEP. The original
+# test only verified the reverse-finish command for a normal call that used
+# the LEP.
+
+if ![supports_reverse] {
+ return
+}
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile] } {
+ return -1
+}
+
+runto_main
+set target_remote [gdb_is_target_remote]
+
+if [supports_process_record] {
+ # Activate process record/replay.
+ gdb_test_no_output "record" "turn on process record for test1"
+}
+
+
+### TEST 1: reverse finish from the entry point instruction (LEP) in
+### function1 when called using the normal entry point (LEP).
+
+# Set breakpoint at call to function1 in main.
+set bp_LEP_test [gdb_get_line_number "CALL VIA LEP" $srcfile]
+gdb_breakpoint $srcfile:$bp_LEP_test temporary
+
+# Continue to break point at function1 call in main.
+gdb_continue_to_breakpoint \
+ "stopped at function1 entry point instruction to stepi into function" \
+ ".*$srcfile:$bp_LEP_test\r\n.*"
+
+# stepi until we see "{" indicating we entered function1
+repeat_cmd_until "stepi" "CALL VIA LEP" "{" "stepi into function1 call" "100"
+
+# The reverse-finish command should stop on the function call instruction
+# which is the last instruction in the source code line. A reverse-next
+# instruction should then stop at the first instruction in the same source
+# code line. Another revers-next instruction stops at the previous source
+# code line.
+gdb_test "reverse-finish" ".*function1 \\(a, b\\); // CALL VIA LEP.*" \
+ "reverse-finish function1 LEP call from LEP "
+gdb_test "reverse-next" ".*function1 \\(a, b\\); // CALL VIA LEP" \
+ "reverse next 1 LEP entry point function call from LEP"
+gdb_test "reverse-next" ".*b = 5;.*" "reverse next 2, at b = 5, call from LEP"
+
+
+gdb_test "reverse-continue" ".*" "setup for test 2"
+
+# Turn off record to clear logs and turn on again
+gdb_test "record stop" "Process record is stopped.*" \
+ "turn off process record for test1"
+gdb_test_no_output "record" "turn on process record for test2"
+
+
+### TEST 2: reverse finish from the body of function1.
+
+# Set breakpoint at call to function1 in main.
+gdb_breakpoint $srcfile:$bp_LEP_test temporary
+
+# Continue to break point at function1 call in main.
+gdb_continue_to_breakpoint \
+ "at function1 entry point instruction to step to body of function" \
+ ".*$srcfile:$bp_LEP_test\r\n.*"
+
+# do a step instruction to get to the body of the function
+gdb_test "step" ".*int ret = 0;.*" "step test 1"
+
+# The reverse-finish command should stop on the function call instruction
+# which is the last instruction in the source code line. A reverse-next
+# instruction should then stop at the first instruction in the same source
+# code line. Another revers-next instruction stops at the previous source
+# code line.
+gdb_test "reverse-finish" ".*function1 \\(a, b\\); // CALL VIA LEP.*" \
+ "reverse-finish function1 LEP call from function body"
+gdb_test "reverse-next" ".*function1 \\(a, b\\); // CALL VIA LEP.*" \
+ "reverse next 1 LEP from function body"
+gdb_test "reverse-next" ".*b = 5;.*" \
+ "reverse next 2 at b = 5, from function body"
+
+gdb_test "reverse-continue" ".*" "setup for test 3"
+
+# Turn off record to clear logs and turn on again
+gdb_test "record stop" "Process record is stopped.*" \
+ "turn off process record for test2"
+gdb_test_no_output "record" "turn on process record for test3"
+
+
+### TEST 3: reverse finish from the alternate entry point instruction (GEP) in
+### function1 when called using the alternate entry point (GEP).
+
+# Set breakpoint at call to funp in main.
+set bp_GEP_test [gdb_get_line_number "CALL VIA GEP" $srcfile]
+gdb_breakpoint $srcfile:$bp_GEP_test temporary
+
+# Continue to break point at funp call in main.
+gdb_continue_to_breakpoint \
+ "stopped at function1 entry point instruction to stepi into funp" \
+ ".*$srcfile:$bp_GEP_test\r\n.*"
+
+# stepi until we see "{" indicating we entered function.
+repeat_cmd_until "stepi" "CALL VIA GEP" "{" "stepi into funp call"
+
+# The reverse-finish command should stop on the function call instruction
+# which is the last instruction in the source code line. A reverse-next
+# instruction should then stop at the first instruction in the same source
+# code line. Another revers-next instruction stops at the previous source
+# code line.
+gdb_test "reverse-finish" ".*funp \\(a, b\\);.*" \
+ "function1 GEP call call from GEP"
+gdb_test "reverse-next" ".*funp \\(a, b\\);.*" \
+ "reverse next 1 GEP entry point function call from GEP"
+gdb_test "reverse-next" ".*b = 50;.*" "reverse next 2 at b = 50, call from GEP"
+
+gdb_test "reverse-continue" ".*" "setup for test 4"
+
+# Turn off record to clear logs and turn on again
+gdb_test "record stop" "Process record is stopped.*" \
+ "turn off process record for test3"
+gdb_test_no_output "record" "turn on process record for test4"
+
+### TEST 4: reverse finish from between the GEP and LEP in
+### function1 when called using the alternate entry point (GEP).
+
+# Set breakpoint at call to funp in main.
+set bp_GEP_test [gdb_get_line_number "CALL VIA GEP" $srcfile]
+gdb_breakpoint $srcfile:$bp_GEP_test temporary
+
+# Continue to break point at funp call in main.
+gdb_continue_to_breakpoint \
+ "stopped at function1 entry point instruction to stepi into funp again" \
+ ".*$srcfile:$bp_GEP_test\r\n.*"
+
+# stepi until we see "{" indicating we entered function.
+repeat_cmd_until "stepi" "CALL VIA GEP" "{" "stepi into funp call again"
+
+# do one more stepi so we are between the GEP and LEP.
+gdb_test "stepi" "{" "stepi to between GEP and LEP"
+
+# The reverse-finish command should stop on the function call instruction
+# which is the last instruction in the source code line. A reverse-next
+# instruction should then stop at the first instruction in the same source
+# code line. Another revers-next instruction stops at the previous source
+# code line.
+gdb_test "reverse-finish" ".*funp \\(a, b\\);.*" \
+ "function1 GEP call call from GEP again"
+gdb_test "reverse-next" ".*funp \\(a, b\\);.*" \
+ "reverse next 1 GEP entry point function call from GEP again"
+gdb_test "reverse-next" ".*b = 50;.*" \
+ "reverse next 2 at b = 50, call from GEP again"
+
+gdb_test "reverse-continue" ".*" "setup for test 5"
+
+# Turn off record to clear logs and turn on again
+gdb_test "record stop" "Process record is stopped.*" \
+ "turn off process record for test4"
+gdb_test_no_output "record" "turn on process record for test5"
+
+
+### TEST 5: reverse finish from the body of function 1 when calling using the
+### alternate entrypoint (GEP).
+gdb_breakpoint $srcfile:$bp_GEP_test temporary
+
+# Continue to break point at funp call.
+gdb_continue_to_breakpoint \
+ "at function1 entry point instruction to step to body of funp call" \
+ ".*$srcfile:$bp_GEP_test\r\n.*"
+
+# Step into body of funp, called via GEP.
+gdb_test "step" ".*int ret = 0;.*" "step test 2"
+
+# The reverse-finish command should stop on the function call instruction
+# which is the last instruction in the source code line. A reverse-next
+# instruction should then stop at the first instruction in the same source
+# code line. Another revers-next instruction stops at the previous source
+# code line.
+gdb_test "reverse-finish" ".*funp \\(a, b\\);.*" \
+ "reverse-finish function1 GEP call, from function body "
+gdb_test "reverse-next" ".*funp \\(a, b\\);.*" \
+ "reverse next 1 GEP call from function body"
+gdb_test "reverse-next" ".*b = 50;.*" \
+ "reverse next 2 at b = 50 from function body"
--
2.37.2