testsuite/gdb.base/sigbpt.exp

# This testcase is part of GDB, the GNU debugger.

# Copyright 2004-2020 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/>.

# Check that GDB can and only executes single instructions when
# stepping through a sequence of breakpoints interleaved by a signal
# handler.

# This test is known to tickle the following problems: kernel letting
# the inferior execute both the system call, and the instruction
# following, when single-stepping a system call; kernel failing to
# propogate the single-step state when single-stepping the sigreturn
# system call, instead resuming the inferior at full speed; GDB
# doesn't know how to software single-step across a sigreturn
# instruction.  Since the kernel problems can be "fixed" using
# software single-step this is KFAILed rather than XFAILed.

if [target_info exists gdb,nosignals] {
    verbose "Skipping sigbpt.exp because of nosignals."
    continue
}


standard_testfile

if {[prepare_for_testing "failed to prepare" $testfile $srcfile debug]} {
    return -1
}

#
# Run to `main' where we begin our tests.
#

if ![runto_main] then {
    fail "can't run to main"
    return 0
}

# If we can examine what's at memory address 0, it is possible that we
# could also execute it.  This could probably make us run away,
# executing random code, which could have all sorts of ill effects,
# especially on targets without an MMU.  Don't run the tests in that
# case.

if { [is_address_zero_readable] } {
    untested "memory at address 0 is possibly executable"
    return
}

gdb_test "break keeper"

# Run to bowler, and then single step until there's a SIGSEGV.  Record
# the address of each single-step instruction (up to and including the
# instruction that causes the SIGSEGV) in bowler_addrs, and the address
# of the actual SIGSEGV in segv_addr.
# Note: this test detects which signal is received.  Usually it is SIGSEGV
# (and we use SIGSEGV in comments) but on Darwin it is SIGBUS.

set bowler_addrs bowler
set segv_addr none
gdb_test {display/i $pc}
gdb_test "advance bowler" "bowler.*" "advance to the bowler"
set test "stepping to fault"
set signame "SIGSEGV"
gdb_test_multiple "stepi" "$test" {
    -re "Program received signal (SIGBUS|SIGSEGV).*pc(\r\n| *) *=> (0x\[0-9a-f\]*).*$gdb_prompt $" {
	set signame $expect_out(1,string)
	set segv_addr $expect_out(3,string)
	pass "$test"
    }
    -re " .*pc(\r\n| *)=> (0x\[0-9a-f\]*).*bowler.*$gdb_prompt $" {
	set bowler_addrs [concat $expect_out(2,string) $bowler_addrs]
	send_gdb "stepi\n"
	exp_continue
    }
}

# Now record the address of the instruction following the faulting
# instruction in bowler_addrs.

set test "get insn after fault"
gdb_test_multiple {x/2i $pc} "$test" {
    -re "=> (0x\[0-9a-f\]*).*bowler.*(0x\[0-9a-f\]*).*bowler.*$gdb_prompt $" {
	set bowler_addrs [concat $expect_out(2,string) $bowler_addrs]
	pass "$test"
    }
}

# Procedures for returning the address of the instruction before, at
# and after, the faulting instruction.

proc before_segv { } {
    global bowler_addrs
    return [lindex $bowler_addrs 2]
}

proc at_segv { } {
    global bowler_addrs
    return [lindex $bowler_addrs 1]
}

proc after_segv { } {
    global bowler_addrs
    return [lindex $bowler_addrs 0]
}

# Check that the address table and SIGSEGV correspond.

set test "verify that ${signame} occurs at the last STEPI insn"
if {[string compare $segv_addr [at_segv]] == 0} {
    pass "$test"
} else {
    fail "$test ($segv_addr [at_segv])"
}

# Check that the inferior is correctly single stepped all the way back
# to a faulting instruction.

proc stepi_out { name args } {
    global gdb_prompt
    global signame

    # Set SIGSEGV to pass+nostop and then run the inferior all the way
    # through to the signal handler.  With the handler is reached,
    # disable SIGSEGV, ensuring that further signals stop the
    # inferior.  Stops a SIGSEGV infinite loop when a broke system
    # keeps re-executing the faulting instruction.
    with_test_prefix $name {
	rerun_to_main
    }
    gdb_test "handle ${signame} nostop print pass" ".*" "${name}; pass ${signame}"
    gdb_test "continue" "keeper.*" "${name}; continue to keeper"
    gdb_test "handle ${signame} stop print nopass" ".*" "${name}; nopass ${signame}"

    # Insert all the breakpoints.  To avoid the need to step over
    # these instructions, this is delayed until after the keeper has
    # been reached.
    for {set i 0} {$i < [llength $args]} {incr i} {
	gdb_test "break [lindex $args $i]" "Breakpoint.*" \
	    "${name}; set breakpoint $i of [llength $args]"
    }

    # Single step our way out of the keeper, through the signal
    # trampoline, and back to the instruction that faulted.
    set test "${name}; stepi out of handler"
    gdb_test_multiple "stepi" "$test" {
	-re "Could not insert single-step breakpoint.*$gdb_prompt $" {
	    setup_kfail gdb/8841 "sparc*-*-openbsd*"
	    fail "$test (could not insert single-step breakpoint)"
	}
	-re "Cannot insert breakpoint.*Cannot access memory.*$gdb_prompt $" {
	    setup_kfail gdb/8841 "nios2*-*-linux*"
	    fail "$test (could not insert single-step breakpoint)"
	}
	-re "keeper.*$gdb_prompt $" {
	    send_gdb "stepi\n"
	    exp_continue
	}
	-re "signal handler.*$gdb_prompt $" {
	    send_gdb "stepi\n"
	    exp_continue
	}
	-re "Program received signal SIGSEGV.*$gdb_prompt $" {
	    kfail gdb/8807 "$test (executed fault insn)"
	}
	-re "Breakpoint.*pc(\r\n| *)[at_segv] .*bowler.*$gdb_prompt $" {
	    pass "$test (at breakpoint)"
	}
	-re "Breakpoint.*pc(\r\n| *)[after_segv] .*bowler.*$gdb_prompt $" {
	    kfail gdb/8807 "$test (executed breakpoint)"
	}
	-re "pc(\r\n| *)[at_segv] .*bowler.*$gdb_prompt $" {
	    pass "$test"
	}
	-re "pc(\r\n| *)[after_segv] .*bowler.*$gdb_prompt $" {
	    kfail gdb/8807 "$test (skipped fault insn)"
	}
	-re "pc(\r\n| *)=> 0x\[a-z0-9\]* .*bowler.*$gdb_prompt $" {
	    kfail gdb/8807 "$test (corrupt pc)"
	}
    }

    # Clear any breakpoints
    for {set i 0} {$i < [llength $args]} {incr i} {
	gdb_test "clear [lindex $args $i]" "Deleted .*" \
	    "${name}; clear breakpoint $i of [llength $args]"
    }
}

# Let a signal handler exit, returning to a breakpoint instruction
# inserted at the original fault instruction.  Check that the
# breakpoint is hit, and that single stepping off that breakpoint
# executes the underlying fault instruction causing a SIGSEGV.

proc cont_out { name args } {
    global gdb_prompt
    global signame

    # Set SIGSEGV to pass+nostop and then run the inferior all the way
    # through to the signal handler.  With the handler is reached,
    # disable SIGSEGV, ensuring that further signals stop the
    # inferior.  Stops a SIGSEGV infinite loop when a broke system
    # keeps re-executing the faulting instruction.
    with_test_prefix $name {
	rerun_to_main
    }
    gdb_test "handle ${signame} nostop print pass" ".*" "${name}; pass ${signame}"
    gdb_test "continue" "keeper.*" "${name}; continue to keeper"
    gdb_test "handle ${signame} stop print nopass" ".*" "${name}; nopass ${signame}"

    # Insert all the breakpoints.  To avoid the need to step over
    # these instructions, this is delayed until after the keeper has
    # been reached.  Always set a breakpoint at the signal trampoline
    # instruction.
    set args [concat $args "*[at_segv]"]
    for {set i 0} {$i < [llength $args]} {incr i} {
	gdb_test "break [lindex $args $i]" "Breakpoint.*" \
	    "${name}; set breakpoint $i  of [llength $args]"
    }

    # Let the handler return, it should "appear to hit" the breakpoint
    # inserted at the faulting instruction.  Note that the breakpoint
    # instruction wasn't executed, rather the inferior was SIGTRAPed
    # with the PC at the breakpoint.
    gdb_test "continue" "Breakpoint.*pc(\r\n| *)=> [at_segv] .*" \
	"${name}; continue to breakpoint at fault"

    # Now single step the faulted instrction at that breakpoint.
    gdb_test "stepi" \
	"Program received signal ${signame}.*pc(\r\n| *)=> [at_segv] .*" \
	"${name}; stepi fault"

    # Clear any breakpoints
    for {set i 0} {$i < [llength $args]} {incr i} {
	gdb_test "clear [lindex $args $i]" "Deleted .*" \
	    "${name}; clear breakpoint $i of [llength $args]"
    }

}


# Try to confuse DECR_PC_AFTER_BREAK architectures by scattering
# breakpoints around the faulting address.  In all cases the inferior
# should single-step out of the signal trampoline halting (but not
# executing) the fault instruction.

stepi_out "stepi"
stepi_out "stepi bp before segv" "*[before_segv]"
stepi_out "stepi bp at segv" "*[at_segv]"
stepi_out "stepi bp before and at segv" "*[at_segv]" "*[before_segv]"


# Try to confuse DECR_PC_AFTER_BREAK architectures by scattering
# breakpoints around the faulting address.  In all cases the inferior
# should exit the signal trampoline halting at the breakpoint that
# replaced the fault instruction.
cont_out "cont"
cont_out "cont bp after segv" "*[before_segv]"
cont_out "cont bp before and after segv" "*[before_segv]" "*[after_segv]"