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

Carl Love via Gdb-patches
2023-03-09T16:10:20Z

Oops, that should have read GDB developers. Sorry about that.

On Wed, 2023-03-08 at 08:19 -0800, Carl Love wrote:
> GCC developers:
>
> Ping. Just wondering if someone could review this patch for
> me. Thanks.
>
> Carl
>
> On Wed, 2023-03-01 at 12:59 -0800, Carl Love wrote:
> > 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"
>
>