Re: [PATCH 2/3] gdb: improve disassembler styling when Pygments raises an exception

[Tom de Vries <tdevries@suse.de>]

On 10/10/22 11:32, Andrew Burgess via Gdb-patches wrote:
> Simon Marchi <simark@simark.ca> writes:
> 
>> On 2022-10-08 12:00, Andrew Burgess wrote:
>>> Simon Marchi <simark@simark.ca> writes:
>>>
>>>>> +# Check that, if the user is using Python Pygments for disassembler
>>>>> +# styling, then the styling correctly switches off when an error is
>>>>> +# detected in the Python code.
>>>>> +proc test_disassembler_error_handling { } {
>>>>> +
>>>>> +    # This test requires the Python Pygments module to be installed
>>>>> +    # and used by GDB.
>>>>> +    if { !$::python_disassembly_styling } {
>>>>> +	return
>>>>> +    }
>>>>> +
>>>>> +    save_vars { env(TERM) } {
>>>>> +	# We need an ANSI-capable terminal to get the output.
>>>>> +	setenv TERM ansi
>>>>> +
>>>>> +	# Restart GDB with the correct TERM variable setting, this
>>>>> +	# means that GDB will enable styling.
>>>>> +	clean_restart_and_disable "restart 4" $::binfile
>>>>> +
>>>>> +	# Disable use of libopcodes for styling.  As this function is
>>>>> +	# only called when Python Pygments module is available, we
>>>>> +	# should now be using that module to style the disassembler
>>>>> +	# output.
>>>>> +	gdb_test_no_output "maint set libopcodes-styling enabled off"
>>>>> +
>>>>> +	# Disassemble a single instruction and ensure that the output
>>>>> +	# has styling markers in it.
>>>>> +	set insn_before [get_single_disassembled_insn]
>>>>> +	gdb_assert { [regexp "\033" $insn_before] } \
>>>>> +	    "have style markers when Pygments is working fine"
>>>>> +
>>>>> +	# Now replace the standard function that colorizes the
>>>>> +	# disassembler output, with a new function that always returns
>>>>> +	# None, this should cause GDB to stop using the Pygments
>>>>> +	# module for disassembler styling.
>>>>> +	gdb_py_test_silent_cmd \
>>>>> +	    [multi_line_input \
>>>>> +		 "python" \
>>>>> +		 "def replacement_colorize_disasm(content,gdbarch):" \
>>>>> +		 "  return None" \
>>>>> +		 "gdb.styling.colorize_disasm = replacement_colorize_disasm" \
>>>>> +		 "\004"] \
>>>>
>>>> Any reason you are using \004 here, instead of end?  I don't quite
>>>> understand why, but it seems to cause some random failures.  Running the
>>>> test under `taskset -c 2` makes it fail most of the time.  Running it
>>>> with check-read1 makes it fail consistently:
>>>>
>>>>    FAIL: gdb.base/style.exp: capture_command_output for x/1i *main
>>>>
>>>> When changing \004 for end, it passes.  I don't have an explanation why
>>>> though.
>>>
>>> It'll be a copy&paste.  There's a couple of other places in the
>>> testsuite where this pattern is used.
>>>
>>> The patch below changes all three to use 'end'.  How's this?
>>>
>>> Thanks,
>>> Andrew
>>
>> This is fine with me, but again, I didn't dig into it so I don't really
>> know what sending a \004 was causing,
> 
> Hi,
> 
> Given you were seeing problems with the use of \004, and the tests
> definitely were not about whether \004 could be used or not, I've pushed
> the patch I proposed (exact version is below).
> 

I found this independently and filed a PR ( 
https://sourceware.org/bugzilla/show_bug.cgi?id=29664 ) and wrote the 
same fix (in the same three test-cases), and was about to commit ...

The FAIL is caused by using gdb_py_test_silent_cmd, which adds a "\n" at 
the end of the command in combination with "\004", causing a stray "\n" 
that generates an extra prompt, which makes the prompt matching 
unpredictable.

Thanks,
- Tom