[Lldb-commits] [PATCH] D40616: ObjectFileELF: Add support for compressed sections

Zachary Turner via lldb-commits lldb-commits at lists.llvm.org
Wed Nov 29 16:33:28 PST 2017

Many reasons.

1) a test that looks like this:

RUN: yaml2obj %p/Inputs/compressed-section.yaml > %t/compressed-section.obj
RUN: lldb-test %s | FileCheck %s

create-module -f %t/compressed-section.obj
dump-module-sections compressed-section.obj

; CHECK: Section: .hello_elf
; CHECK-NEXT: Size: 9
; CHECK-NEXT: Data: Hello ELF

; CHECK: Section: .bogus
; CHECK-NEXT: Size: 0

takes about 1 minute to write, and a couple of seconds to understand, and
is 12 lines of code, compared to a unit test which takes significantly
longer to write and understand, and is (at least in this case) 37 lines not
counting the code to implement the command

2) this is a standard test format that is understood by hundreds of

3) It does not contribute to build time.

4) Any work you do to implement the `create-module` and
`dump-module-sections` testing command can later be used by any other test
without any additional code.  With a reasonable set of commands you would
reach a point where you were rarely having to update the tool.

5) Parsing text output is often the most straightforward and easiest way to
verify something.  Consider for example a testcommand like
"dump-unwind-plan" where you could easily represent an unwind plan in text
as a sequence of rules and/or heuristics.  Try doing that in code, for
several hundred different test cases of obscure unwind scenarios and I
think you'll quickly give up and decide it's more trouble than it's worth.

On Wed, Nov 29, 2017 at 4:14 PM Jim Ingham <jingham at apple.com> wrote:

> > On Nov 29, 2017, at 3:46 PM, Zachary Turner <zturner at google.com> wrote:
> >
> > FWIW, it can certainly use the SB API where it makes sense, but I think
> requiring that it only use the SB API would be very limiting and a big
> mistake.
> >
> > The entire point of a tool such as this is that it allows you to dig
> deep into internals that would be difficult to access otherwise.
> I'm not sure about that.  Making a test that "digs deep into internals" in
> this method is almost certainly going to require writing a custom command
> in lldb-test to poke those API's.  How would this be any easier than
> writing a unit test?
> Jim
> >
> > On Wed, Nov 29, 2017 at 3:23 PM Jason Molenda <jmolenda at apple.com>
> wrote:
> >
> >
> > > On Nov 29, 2017, at 2:51 PM, Zachary Turner via lldb-commits <
> lldb-commits at lists.llvm.org> wrote:
> > >
> > >
> > >
> > > On Wed, Nov 29, 2017 at 1:59 PM Jim Ingham <jingham at apple.com> wrote:
> > > I'm mostly basing this concern on the bad effect this had on gdb all
> of whose testing was expect based command scraping.  gdb is a tool that's
> much closer to lldb than any of the compiler tools so that experience seems
> relevant.  It's been a decade or so since I worked on gdb, but back when I
> was working on it, you really had to tread very carefully if you wanted to
> change the output of, say, the break command, or to thread listings, etc,
> and a bunch of times I just had to bag some cleanup of output I wanted to
> do because fixing up all the tests was too time consuming.  Because Jason
> and I had both had this experience when we started working on lldb, we
> promised ourselves we wouldn't go down this path again...
> > >
> > >
> > > Couple of things:
> > >
> > > 1) I wouldn't dare to use this approach for anything that required
> interactivity.  If you need to run one command, extract a value from the
> output, and use that value as input to another command, I think that would
> be a big mistake.  I have no intention of ever proposing something like
> that.
> > >
> > > 2) FileCheck is very flexible in the way it matches output and tests
> can be written so that they are resilient to minor format tweaks.  I have
> no doubt that with pure regex matching, or with pretty much any other tool,
> you would have a really bad time.  Of course, that doesn't mean it would be
> hard to construct an example of a format change that would break a
> FileCheck test.  But I think it would happen *far* less frequently than it
> did on GDB.  That said, I still understand your concerns that it's fragile,
> so...
> > >
> > > 3) I would not be opposed to a tool called lldb-test, which was
> basically just LLDB with a different, and much more limited set of
> commands, and was completely non-interactive and would produce output in a
> format designed for being scraped, and which never had to be changed since
> it was never presented to the user.
> >
> >
> > 100% agree with #3.  We could go back and forth about using lldb-mi, but
> I think a specialized driver using SB API, designed for testing, would be a
> great approach.
> >
> >
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