[lldb-dev] Using FileCheck in lldb inline tests

Tue Aug 14 18:39:39 PDT 2018

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.

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,

(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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