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arc: Determine a branch target of DBNZ correctly

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DBNZ instruction was moved from BRANCH class to a separate one - DBNZ.
Thus, it must be processed separately in arc_insn_get_branch_target
to correctly determine an offset for a possible branch.

The testsuite for DBNZ instruction verifies these cases:

     1. Check that dbnz does not branch and falls through if its source
        register is 0 after decrementing. GDB must successfully break
        on the following instruction after stepping over.
     2. Check that dbnz branches to the target correctly if its source register
        is not 0 after decrementing - GDB must successfully break on the target
        instruction if a forward branch is performed after stepping over.
     3. The same as point 2 but for a backward branching case.

Signed-off-by: Yuriy Kolerov <kolerov93@gmail.com>
This commit is contained in:
Yuriy Kolerov
2024-02-14 18:16:16 +00:00
committed by Shahab Vahedi
parent f961273101
commit 33283d91d9
3 changed files with 154 additions and 0 deletions
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10
gdb/arc-tdep.c
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@@ -466,6 +466,16 @@ arc_insn_get_branch_target (const struct arc_instruction &insn)
instruction, hence last two bits should be truncated. */
return pcrel_addr + align_down (insn.address, 4);
}
/* DBNZ is the only branch instruction that keeps a branch address in
the second operand. It must be intercepted and treated differently. */
else if (insn.insn_class == DBNZ)
{
CORE_ADDR pcrel_addr = arc_insn_get_operand_value_signed (insn, 1);
/* Offset is relative to the 4-byte aligned address of the current
instruction, hence last two bits should be truncated. */
return pcrel_addr + align_down (insn.address, 4);
}
/* B, Bcc, BL, BLcc, LP, LPcc: PC = currentPC + operand. */
else if (insn.insn_class == BRANCH || insn.insn_class == LOOP)
{

47
gdb/testsuite/gdb.arch/arc-dbnz.S Normal file
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@@ -0,0 +1,47 @@
; This testcase is part of GDB, the GNU debugger.
; Copyright 2024 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/>.
.section .text
.align 4
.global main
.type main, @function
main:
mov r0,1
dbnz1:
; r0 == 0 after decrementing. dbnz doesn't do branch.
dbnz r0,@end
mov r0,5
dbnz2:
; r0 == 3 after decrementing and delay slot. dbnz does branch.
dbnz.d r0,@dbnz3
sub r0,r0,1
dbnz4:
; r0 == 1 after decrementing. dbnz does branch.
dbnz r0,@end
dbnz3:
; r0 == 2 after decrementing. dbnz does branch.
dbnz r0,@dbnz4
end:
mov r0,0
j [blink]
.section .note.GNU-stack,"",@progbits

97
gdb/testsuite/gdb.arch/arc-dbnz.exp Normal file
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@@ -0,0 +1,97 @@
# This testcase is part of GDB, the GNU debugger.
# Copyright 2024 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/>.
# Test dbnz instruction. It decrements its source register operand, and if
# the result is non-zero it branches to the location defined by a signed
# half-word displacement operand.
#
# It's necessary to verify these cases:
#
# 1. Check that dbnz does not branch and falls through if its source
# register is 0 after decrementing. GDB must successfully break
# on the following instruction after stepping over.
# 2. Check that dbnz branches to the target correctly if its source register
# is not 0 after decrementing - GDB must successfully break on the target
# instruction if a forward branch is performed after stepping over.
# 3. The same as point 2 but for a backward branching case.
require {istarget "arc*-*-*"}
standard_testfile .S
if { [prepare_for_testing "failed to prepare" $testfile $srcfile] } {
return -1
}
if ![runto_main] {
return 0
}
gdb_test "break dbnz1" \
"Breakpoint $decimal at .*" \
"set breakpoint on the 1st dbnz"
gdb_test "break dbnz2" \
"Breakpoint $decimal at .*" \
"set breakpoint on the 2nd dbnz"
gdb_test "break dbnz3" \
"Breakpoint $decimal at .*" \
"set breakpoint on the 3rd dbnz"
gdb_test "break dbnz4" \
"Breakpoint $decimal at .*" \
"set breakpoint on the 4th dbnz"
gdb_test "break end" \
"Breakpoint $decimal at .*" \
"set breakpoint at the end"
gdb_test "continue" \
"Breakpoint $decimal, dbnz1.*dbnz r0,@end" \
"continue to the 1st dbnz"
gdb_test "x /i \$pc" \
"$hex <.*>:\[ \t\]+dbnz\[ \t\]+r0,24.*" \
"stayng on the 1st dbnz instruction"
gdb_test "stepi" \
"mov r0,5" \
"step over the 1st dbnz, branch is not taken"
gdb_test "stepi" \
"Breakpoint $decimal, dbnz2.*dbnz\\.d r0,@dbnz3" \
"step over r0 initialization, staying on the 2nd dbnz"
# Linux steps over delay slot after "stepi", but stubs with hardware stepping
# like nSIM's stub may step right on delay slot. Thus use "continue" instead of
# "stepi" to make this test work for all platforms.
gdb_test "continue" \
"Breakpoint $decimal, dbnz3.*dbnz r0,@dbnz4" \
"step over the 2nd dbnz, branch is taken, staying on the 3rd dbnz"
gdb_test "stepi" \
"Breakpoint $decimal, dbnz4.*dbnz r0,@end" \
"step over the 3rd dbnz, branch is taken, staying on the 4th dbnz"
gdb_test "stepi" \
"Breakpoint $decimal, end.*mov r0,0" \
"step over the 4th dbnz, branch is taken, staying on the epilogue"
gdb_test "info register r0" \
"r0\[ \t\]+0x1\[ \t\]+1" \
"r0 contains 1 after all dbnz instructions"