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Harden gdb.base/step-over-syscall.exp 

New in v3:
- Verify if the syscall number matches what is expected for the target.
- Used gdb_assert for one more check.

New in v2:

- Set initial values to -1 instead of 0.
- Rewrote RE to prevent unexpected matching when parsing one character at a
  time.
- Used gdb_assert for an additional check.
- Validated with check-read1

There are a couple problems with this test.

First
--

gdb.base/step-over-syscall.exp records the address of a syscall instruction
within fork/vfork/clone functions and also the address of the instruction
after that syscall instruction.

It uses these couples addresses to make sure we stepped over a syscall
instruction (fork/vfork/clone events) correctly.

The way the test fetches the addresses of the instructions is by stepi-ing
its way through the fork/vfork/clone functions until it finds a match for
a syscall. Then it stepi's once again to get the address of the next
instruction.

This assumes that stepi-ing over a syscall is working correctly and landing
in the right PC. This is not the case for AArch64/Linux, where we're
landing a couple instructions after the syscall in some cases.

The following patch lets the test execute as before, but adds a new instruction
address check using the x command as opposed to stepi.

I didn't want to change how the test works since we may also be
interested in checking if stepi-ing over the syscall under different
conditions (displaced stepping on/off) yields the same results. I don't
feel strongly about this, so i'm OK with changing how we compare PC's for
the entire test if folks decide it is reasonable.

Second
--

FAIL: gdb.base/step-over-syscall.exp: vfork: displaced=off: continue to vfork (3rd time) (the program exited)
FAIL: gdb.base/step-over-syscall.exp: vfork: displaced=off: continue to syscall insn vfork (the program is no longer running)
FAIL: gdb.base/step-over-syscall.exp: vfork: displaced=off: single step over vfork (the program is no longer running)

Depending on the glibc version we may have different code generated for the
fork/vfork/clone functions.

I ran into the situation where vfork for newer glibc's on AArch64/Linux is
very short, so "break vfork" will put a breakpoint right at the syscall
instruction, which is something the testcase isn't expecting (a off-by-1
of sorts).

The patch adds extra code to handle this case. If the test detects we're
already sitting at a syscall instruction, it records the address and moves
on to record the address after that particular instruction.

Another measure is to "break *$syscall" instead of "break $syscall". That
guarantees we're stopping at the first instruction of the syscall function,
if it ever happens that the syscall instruction is the first instruction of
those functions.

With these changes i can fix some failures for aarch64-linux-gnu and also
expose the problems i've reported here:

https://sourceware.org/ml/gdb-patches/2019-12/msg01071.html

These tests now fail for aarch64-linux-gnu (patch for this is going through
reviews):

FAIL: gdb.base/step-over-syscall.exp: vfork: displaced=off: pc after stepi matches insn addr after syscall
FAIL: gdb.base/step-over-syscall.exp: vfork: displaced=on: pc after stepi matches insn addr after syscall

gdb/testsuite/ChangeLog:

2020-01-27  Luis Machado  <luis.machado@linaro.org>

	* gdb.base/step-over-syscall.exp (setup): Check if we're already
	sitting at a syscall instruction when we hit the syscall function's
	breakpoint.
	Check PC against one obtained with the x command.
	Validate syscall number.
	(step_over_syscall): Don't continue to the syscall instruction if
	we're already there.
This commit is contained in:
Luis Machado 2020-01-14 13:46:07 -03:00
parent 82ef9cad78
commit 16b10d6e61
2 changed files with 111 additions and 33 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
gdb/testsuite/ChangeLog
View File

@ -1,3 +1,13 @@
2020-01-27 Luis Machado <luis.machado@linaro.org>
* gdb.base/step-over-syscall.exp (setup): Check if we're already
sitting at a syscall instruction when we hit the syscall function's
breakpoint.
Check PC against one obtained with the x command.
Validate syscall number.
(step_over_syscall): Don't continue to the syscall instruction if
we're already there.
2020-01-25 Philippe Waroquiers <philippe.waroquiers@skynet.be>
* gdb.base/attach.exp: Test 'set exec-file-mismatch'.

134
gdb/testsuite/gdb.base/step-over-syscall.exp
View File

@ -16,13 +16,27 @@
# along with this program. If not, see <http://www.gnu.org/licenses/>.
set syscall_insn ""
set syscall_register ""
array set syscall_number {}
# Define the syscall instruction for each target.
# Define the syscall instructions, registers and numbers for each target.
if { [istarget "i\[34567\]86-*-linux*"] || [istarget "x86_64-*-linux*"] } {
set syscall_insn "\[ \t\](int|syscall|sysenter)\[ \t\]"
set syscall_register "eax"
array set syscall_number {fork "(56|120)" vfork "(58|190)" \
clone "(56|120)"}
} elseif { [istarget "aarch64*-*-linux*"] || [istarget "arm*-*-linux*"] } {
set syscall_insn "\[ \t\](swi|svc)\[ \t\]"
if { [istarget "aarch64*-*-linux*"] } {
set syscall_register "x8"
} else {
set syscall_register "r7"
}
array set syscall_number {fork "(120|220)" vfork "(190|220)" \
clone "(120|220)"}
} else {
return -1
}
@ -30,13 +44,22 @@ if { [istarget "i\[34567\]86-*-linux*"] || [istarget "x86_64-*-linux*"] } {
proc_with_prefix check_pc_after_cross_syscall { syscall syscall_insn_next_addr } {
set syscall_insn_next_addr_found [get_hexadecimal_valueof "\$pc" "0"]
set test "single step over $syscall final pc"
if {$syscall_insn_next_addr != 0
&& $syscall_insn_next_addr == $syscall_insn_next_addr_found} {
pass $test
} else {
fail $test
}
gdb_assert {$syscall_insn_next_addr != 0 \
&& $syscall_insn_next_addr == $syscall_insn_next_addr_found} \
"single step over $syscall final pc"
}
# Verify the syscall number is the correct one.
proc syscall_number_matches { syscall } {
global syscall_register syscall_number
if {[gdb_test "p \$$syscall_register" ".*= $syscall_number($syscall)" \
"syscall number matches"] != 0} {
return 0
}
return 1
}
# Restart GDB and set up the test. Return a list in which the first one
@ -47,6 +70,8 @@ proc_with_prefix check_pc_after_cross_syscall { syscall syscall_insn_next_addr }
proc setup { syscall } {
global gdb_prompt syscall_insn
global hex
set next_insn_addr -1
set testfile "step-over-$syscall"
clean_restart $testfile
@ -62,7 +87,7 @@ proc setup { syscall } {
gdb_test_no_output "set displaced-stepping off" \
"set displaced-stepping off during test setup"
gdb_test "break $syscall" "Breakpoint \[0-9\]* at .*"
gdb_test "break \*$syscall" "Breakpoint \[0-9\]* at .*"
gdb_test "continue" "Continuing\\..*Breakpoint \[0-9\]+, (.* in |__libc_|)$syscall \\(\\).*" \
"continue to $syscall (1st time)"
@ -75,39 +100,77 @@ proc setup { syscall } {
# Hit the breakpoint on $syscall for the second time. In this time,
# the address of syscall insn and next insn of syscall are recorded.
gdb_test "display/i \$pc" ".*"
# Check if the first instruction we stopped at is the syscall one.
set syscall_insn_addr -1
gdb_test_multiple "display/i \$pc" "fetch first stop pc" {
-re "display/i .*: x/i .*=> ($hex) .*:.*$syscall_insn.*$gdb_prompt $" {
set insn_addr $expect_out(1,string)
# Single step until we see a syscall insn or we reach the
# upper bound of loop iterations.
set msg "find syscall insn in $syscall"
set steps 0
set max_steps 1000
gdb_test_multiple "stepi" $msg {
-re ".*$syscall_insn.*$gdb_prompt $" {
pass $msg
# Is the syscall number the correct one?
if {[syscall_number_matches $syscall]} {
set syscall_insn_addr $insn_addr
}
pass $gdb_test_name
}
-re "x/i .*=>.*\r\n$gdb_prompt $" {
incr steps
if {$steps == $max_steps} {
fail $msg
} else {
send_gdb "stepi\n"
exp_continue
-re ".*$gdb_prompt $" {
pass $gdb_test_name
}
}
# If we are not at the syscall instruction yet, keep looking for it with
# stepi commands.
if {$syscall_insn_addr == -1} {
# Single step until we see a syscall insn or we reach the
# upper bound of loop iterations.
set steps 0
set max_steps 1000
gdb_test_multiple "stepi" "find syscall insn in $syscall" {
-re ".*$syscall_insn.*$gdb_prompt $" {
# Is the syscall number the correct one?
if {[syscall_number_matches $syscall]} {
pass $gdb_test_name
} else {
exp_continue
}
}
-re "x/i .*=>.*\r\n$gdb_prompt $" {
incr steps
if {$steps == $max_steps} {
fail $gdb_test_name
} else {
send_gdb "stepi\n"
exp_continue
}
}
}
if {$steps == $max_steps} {
return { -1, -1 }
}
}
if {$steps == $max_steps} {
return { -1, -1 }
# We have found the syscall instruction. Now record the next instruction.
# Use the X command instead of stepi since we can't guarantee
# stepi is working properly.
gdb_test_multiple "x/2i \$pc" "pc before/after syscall instruction" {
-re "x/2i .*=> ($hex) .*:.*$syscall_insn.* ($hex) .*:.*$gdb_prompt $" {
set syscall_insn_addr $expect_out(1,string)
set next_insn_addr $expect_out(3,string)
pass $gdb_test_name
}
}
set syscall_insn_addr [get_hexadecimal_valueof "\$pc" "0" \
"pc before stepi"]
if {[gdb_test "stepi" "x/i .*=>.*" "stepi $syscall insn"] != 0} {
return { -1, -1 }
}
return [list $syscall_insn_addr [get_hexadecimal_valueof "\$pc" \
"0" "pc after stepi"]]
set pc_after_stepi [get_hexadecimal_valueof "\$pc" "0" \
"pc after stepi"]
gdb_assert {$next_insn_addr == $pc_after_stepi} \
"pc after stepi matches insn addr after syscall"
return [list $syscall_insn_addr $pc_after_stepi]
}
proc step_over_syscall { syscall } {
@ -156,8 +219,13 @@ proc step_over_syscall { syscall } {
}
}
gdb_test "continue" "Continuing\\..*Breakpoint \[0-9\]+, .*" \
"continue to syscall insn $syscall"
# Check if the syscall breakpoint is at the syscall instruction
# address. If so, no need to continue, otherwise we will run the
# inferior to completion.
if {$syscall_insn_addr != [get_hexadecimal_valueof "\$pc" "0"]} {
gdb_test "continue" "Continuing\\..*Breakpoint \[0-9\]+, .*" \
"continue to syscall insn $syscall"
}
gdb_test_no_output "set displaced-stepping $displaced"