Re: [PATCH] gdb/testsuite: Fix race in gdb.dwarf2/calling-convention.exp

[Pedro Alves <pedro@palves.net>]

On 2022-03-30 13:50, Lancelot SIX via Gdb-patches wrote:
> Pedro Alves warned me that there is a race in
> gdb.dwarf2/calling-convention.exp making the test sometimes fail on his
> setup.  This can be reliably reproduced using :
> 
>     make check-read1 TESTS="gdb.dwarf2/calling-convention.exp"
> 
> The relevant part of the gdb.log file is:
> 
>     return 35
>     Function 'foo' does not follow the target calling convention.
>     If you continue, setting the return value will probably lead to unpredictable behaviors.
>     Make foo return now? (y or n) PASS: gdb.dwarf2/calling-convention.exp: return 35
>     n
>     Not confirmed
>     (gdb) FAIL: gdb.dwarf2/calling-convention.exp: finish
> 
> The issue is that when doing the test for "return 35", the DejaGnu test
> sends "n" (to tell GDB not to perform the return action) but never
> consumes the "Not confirmed" acknowledgment sent by GDB.  Later, when
> trying to do the next test, DejaGnu tries to match the leftover output
> from the "return" test. As this output is not expected, the test fails.
> 
> Fix this by consuming the "Not confirmed\r\n$gdb_prompt " output.
> 
> While at cleaning up this test, also improve the regex for the return
> test:
> - Remove the leading ".*" pattern.
> - Replace the "$" (end of line marker) with "\$" because it does not
>   identify a TCL variable.

I don't think the latter is necessary.  If it was, then the >3k instances
we have would be problematic:

 $ grep -rn " $\"" testsuite/ | wc -l
 3497

>  gdb_test_multiple "return 35" "" {
> -    -re ".*Function 'foo' does not follow the target calling convention.\r\nIf you continue, setting the return value will probably lead to unpredictable behaviors.\r\nMake foo return now?.*\\(y or n\\) $" {
> -	send_gdb "n\n"
> +    -re "Function 'foo' does not follow the target calling convention.\r\nIf you continue, setting the return value will probably lead to unpredictable behaviors.\r\nMake foo return now?.*\\(y or n\\) \$" {

This should escape the "?" in "now?" too, as '?' has special meaning in regexps.

The ".*" just before (y or n) isn't needed, right?

>  	pass $gdb_test_name
> +	gdb_test "n" "Not confirmed" "Cancel return"

Lowercase messages please.

Note gdb_test can handle this itself, it supports two extra arguments to handle questions.  Like so:

gdb_test "return 35" \
    "Not confirmed" \
    "return 35" \
    "Function 'foo' does not follow the target calling convention.\r\nIf you continue, setting the return value will probably lead to unpredictable behaviors.\r\nMake foo return now\\? \\(y or n\\) $" \
    "n"

Note that if gdb doesn't print the question and prints "Not confirmed" straight away, the test will still pass, because
the question is optional.  IMHO that's a gdb_test misfeature, though, which can lead to regressions without us noticing.
I wrote a patch to change that, and it caught a number of wrong things in the testsuite.  I'll send it a bit later.