[lldb-dev] Using FileCheck in lldb inline tests

Wed Aug 15 11:44:02 PDT 2018

> On Aug 14, 2018, at 6:58 PM, Jason Molenda <jmolenda at apple.com> wrote:
> 
> 
> 
>> On Aug 14, 2018, at 6:39 PM, Zachary Turner <zturner at google.com> wrote:
>> 
>> Having bugs also makes the debugger harder to innovate in the future because it’s, not having tests leads to having bugs, and sb api tests leads to not having tests. At the end of the day, it doesn’t matter how stable the tests are if there arent enough of them. There should be about 10x-20x as many tests as there are currently, and that will simply never happen under the current approach. If it means we need to have multiple different styles of test, so be it. The problem we face right now has nothing to do with command output changing, and in fact I don’t that we’ve *ever* had this problem. So we should be focusing on problems we have, not problems we don’t have.
> 
> 
> I think we've had this discussion many times over the years, so I apologize for not reiterating what I've said in the past.  I worked on gdb for a decade before this, where the entire testsuite was filecheck style tests based on gdb's output.  It made it easy for them to write, and after a couple decades of tests had accumulated, it became a nightmare to change or improve any of gdb's commands, we all avoided it like the plague because it was so onerous.  The tests themselves would accumulate more and more complicated regular expressions to handle different output that happened to be seen, so debugging WHY a given test was failing required an amazing amount of work.

Yep, I definitely sympathize with this issue. We have this problem of having large, hard-to-parse pattern-matching tests in the frontends (some specific IRGen tests come to mind...). Again, I think the solution here is more active code review and using alternative representations of the input of interest. It's usually possible to simplify these tests substantially by having an even more compact, simplified dump of the internal representation to check against. This is what we did for clang/swift's code coverage IRGen tests and it's worked really well.

> Yes, lldb does not have these problems -- because we learned from our decades working on gdb, and did not repeat that mistake.  To be honest, lldb is such a young debugger - barely a decade old, depending on how you count it, that ANY testsuite approach would be fine at this point.  Add a couple more decades and we'd be back into the hole that gdb was in.  {I have not worked on gdb in over a decade, so I don't know how their testing methodology may be today}
> 
> It's always important to remember that lldb is first and foremost a debugger library.  It also includes a driver program, lldb, but it is designed as a library and it should be tested as a library.

I broadly agree with your points here, but I'm not convinced that the only acceptable form of testing for lldb is based on sb api tests. I think the only way to an acceptable level of test coverage is to enable expressive testing on compact input. Moreover I don't think that's incompatible with having sufficient API test coverage.

vedant

> 
> 
>> 
>> Note that it is not strictly necessary for a test to check the debuggers command output. There could be a different set of commands whose only purpose is to print information for the purposes of debugging. One idea would be to introduce the notion of a debugger object model, where you print various aspects of the debuggers state with an object like syntax. For example,
> 
> This was the whole point of the lit tests, wasn't it?  To have a driver program, or driver programs, designed explicitly for filecheck, where the output IS API and can be relied on.  There hasn't been disagreement about this.
> 
>> 
>> (lldb) p debugger.targets
>> ~/foo (running, pid: 123)
>> 
>> (lldb) p debugger.targets[0].threads[0].frames[1]
>> int main(int argc=3, char **argv=0x12345678) + 0x72
>> 
>> (lldb) p debugger.targets[0].threads[0].frames[1].params[0]
>> int argc=3
>> 
>> (lldb) p debugger.targets[0].breakpoints
>> [1] main.cpp:72
>> 
>> Etc. you can get arbitrarily granular and dxpose every detail of the debuggers internal state this way, and the output is so simple that you never have to worry about it changing.
>> 
>> That said, I think history has shown that limiting ourselves to sb api tests, despite all the theoretical benefits, leads to insufficient test coverage. So while it has benefits, it also has problems for which we need a better solution
>> On Tue, Aug 14, 2018 at 6:19 PM Jason Molenda via lldb-dev <lldb-dev at lists.llvm.org> wrote:
>> It's more verbose, and it does mean test writers need to learn the public API, but it's also much more stable and debuggable in the future.  It's a higher up front cost but we're paid back in being able to develop lldb more quickly in the future, where our published API behaviors are being tested directly, and the things that must not be broken.  The lldb driver's output isn't a contract, and treating it like one makes the debugger harder to innovate in the future.
>> 
>> It's also helpful when adding new features to ensure you've exposed the feature through the API sufficiently.  The first thing I thought to try when writing the example below was SBFrame::IsArtificial() (see SBFrame::IsInlined()) which doesn't exist.  If a driver / IDE is going to visually indicate artificial frames, they'll need that.
>> 
>> J
>> 
>>> On Aug 14, 2018, at 5:56 PM, Vedant Kumar <vsk at apple.com> wrote:
>>> 
>>> It'd be easy to update FileCheck tests when changing the debugger (this happens all the time in clang/swift). OTOH, the verbosity of the python API means that fewer tests get written. I see a real need to make expressive tests easier to write.
>>> 
>>> vedant
>>> 
>>>> On Aug 14, 2018, at 5:38 PM, Jason Molenda <jmolenda at apple.com> wrote:
>>>> 
>>>> I'd argue against this approach because it's exactly why the lit tests don't run against the lldb driver -- they're hardcoding the output of the lldb driver command into the testsuite and these will eventually make it much more difficult to change and improve the driver as we've accumulated this style of test.
>>>> 
>>>> This is a perfect test for a normal SB API.  Run to your breakpoints and check the stack frames.
>>>> 
>>>> f0 = thread.GetFrameAtIndex(0)
>>>> check that f0.GetFunctionName() == sink
>>>> check that f0.IsArtifical() == True
>>>> check that f0.GetLineEntry().GetLine() == expected line number
>>>> 
>>>> 
>>>> it's more verbose, but it's also much more explicit about what it's checking, and easy to see what has changed if there is a failure.
>>>> 
>>>> 
>>>> J
>>>> 
>>>>> On Aug 14, 2018, at 5:31 PM, Vedant Kumar via lldb-dev <lldb-dev at lists.llvm.org> wrote:
>>>>> 
>>>>> Hello,
>>>>> 
>>>>> I'd like to make FileCheck available within lldb inline tests, in addition to existing helpers like 'runCmd' and 'expect'.
>>>>> 
>>>>> My motivation is that several tests I'm working on can't be made as rigorous as they need to be without FileCheck-style checks. In particular, the 'matching', 'substrs', and 'patterns' arguments to runCmd/expect don't allow me to verify the ordering of checked input, to be stringent about line numbers, or to capture & reuse snippets of text from the input stream.
>>>>> 
>>>>> I'd curious to know if anyone else is interested or would be willing to review this (https://reviews.llvm.org/D50751).
>>>>> 
>>>>> Here's an example of an inline test which benefits from FileCheck-style checking. This test is trying to check that certain frames appear in a backtrace when stopped inside of the "sink" function. Notice that without FileCheck, it's not possible to verify the order in which frames are printed, and that dealing with line numbers would be cumbersome.
>>>>> 
>>>>> ```
>>>>> --- a/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/main.cpp
>>>>> +++ b/lldb/packages/Python/lldbsuite/test/functionalities/tail_call_frames/unambiguous_sequence/main.cpp
>>>>> @@ -9,16 +9,21 @@
>>>>> 
>>>>> volatile int x;
>>>>> 
>>>>> +// CHECK: frame #0: {{.*}}sink() at main.cpp:[[@LINE+2]] [opt]
>>>>> void __attribute__((noinline)) sink() {
>>>>> -  x++; //% self.expect("bt", substrs = ['main', 'func1', 'func2', 'func3', 'sink'])
>>>>> +  x++; //% self.filecheck("bt", "main.cpp")
>>>>> }
>>>>> 
>>>>> +// CHECK-NEXT: frame #1: {{.*}}func3() {{.*}}[opt] [artificial]
>>>>> void __attribute__((noinline)) func3() { sink(); /* tail */ }
>>>>> 
>>>>> +// CHECK-NEXT: frame #2: {{.*}}func2() at main.cpp:[[@LINE+1]] [opt]
>>>>> void __attribute__((disable_tail_calls, noinline)) func2() { func3(); /* regular */ }
>>>>> 
>>>>> +// CHECK-NEXT: frame #3: {{.*}}func1() {{.*}}[opt] [artificial]
>>>>> void __attribute__((noinline)) func1() { func2(); /* tail */ }
>>>>> 
>>>>> +// CHECK-NEXT: frame #4: {{.*}}main at main.cpp:[[@LINE+2]] [opt]
>>>>> int __attribute__((disable_tail_calls)) main() {
>>>>> func1(); /* regular */
>>>>> return 0;
>>>>> ```
>>>>> 
>>>>> For reference, here's the output of the "bt" command:
>>>>> 
>>>>> ```
>>>>> runCmd: bt
>>>>> output: * thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
>>>>> * frame #0: 0x000000010c6a6f64 a.out`sink() at main.cpp:14 [opt]
>>>>>  frame #1: 0x000000010c6a6f70 a.out`func3() at main.cpp:15 [opt] [artificial]
>>>>>  frame #2: 0x000000010c6a6f89 a.out`func2() at main.cpp:21 [opt]
>>>>>  frame #3: 0x000000010c6a6f90 a.out`func1() at main.cpp:21 [opt] [artificial]
>>>>>  frame #4: 0x000000010c6a6fa9 a.out`main at main.cpp:28 [opt]
>>>>> ```
>>>>> 
>>>>> thanks,
>>>>> vedant
>>>>> _______________________________________________
>>>>> lldb-dev mailing list
>>>>> lldb-dev at lists.llvm.org
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
>>>> 
>>> 
>> 
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