From 75312ae3ab577c3a72ada54512533fec8bfae7bb Mon Sep 17 00:00:00 2001 From: Kevin Buettner Date: Fri, 2 Jun 2017 17:58:12 -0700 Subject: [PATCH] Use noncapturing subpattern/parens in gdb_test implementation This is the portion of gdb_test which performs the match against the RE (regular expression) passed to it: return [gdb_test_multiple $command $message { -re "\[\r\n\]*($pattern)\[\r\n\]+$gdb_prompt $" { if ![string match "" $message] then { pass "$message" } } In a test that I've been working on recently, I wanted to use a backreference - that's the \1 in the the RE below: gdb_test "info threads" \ {.*[\r\n]+\* +([0-9]+) +Thread[^\r\n]* do_something \(n=\1\) at.*} Put into English, I wanted to make sure that the value of n passed to do_something() is the same as the thread number shown in the "info threads" Id column. (I've structured the test case so that this *should* be the case.) It didn't work though. It turned out that ($pattern) in the RE noted above is capturing the attempted backreference. So, in this case, the backreference does not refer to ([0-9]+) as intended, but instead refers to ($pattern). This is wrong because it's not what I intended, but is also wrong because, if allowed, it could only match a string of infinite length. This problem can be fixed by using parens for a "noncapturing subpattern". The way that this is done, syntactically, is to use (?:$pattern) instead of ($pattern). My research shows that this feature has been present since tcl8.1 which was released in 1999. The current tcl version is 8.6 - at least that's what I have on my machine. It appears to me that mingw uses some subversion of tcl8.4 which will also have this feature (since 8.4 > 8.1). So it seems to me that any platform upon which we might wish to test GDB will have a version of tcl which has this feature. That being the case, my hope is that there won't be any objections to its use. When I looked at the implementation of gdb_test, I wondered whether the parens were needed at all. I've concluded that they are. In the event that $pattern is an RE which uses alternation at the top level, e.g. a|b, we need to make $pattern a subpattern (via parens) to limit the extend of the alternation. I.e, we don't want the alternation to extend to the other portions of the RE which gdb_test uses to match potential blank lines at the beginning of the pattern or the gdb prompt at the end. gdb/testsuite/ChangeLog: * gdb.exp (gdb_test): Using noncapturing parens for the $pattern subpattern. --- gdb/testsuite/ChangeLog | 5 +++++ gdb/testsuite/lib/gdb.exp | 2 +- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog index 5b71fec..253e229 100644 --- a/gdb/testsuite/ChangeLog +++ b/gdb/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2017-06-21 Kevin Buettner + + * gdb.exp (gdb_test): Using noncapturing parens for the $pattern + subpattern. + 2017-06-19 Peter Bergner * gdb.arch/powerpc-power9.exp: Update test case for new lnia diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp index a74f974..3d3eaab 100644 --- a/gdb/testsuite/lib/gdb.exp +++ b/gdb/testsuite/lib/gdb.exp @@ -1000,7 +1000,7 @@ proc gdb_test { args } { } return [gdb_test_multiple $command $message { - -re "\[\r\n\]*($pattern)\[\r\n\]+$gdb_prompt $" { + -re "\[\r\n\]*(?:$pattern)\[\r\n\]+$gdb_prompt $" { if ![string match "" $message] then { pass "$message" } -- 2.7.4