[cfe-dev] How does scan-build

[Ben Craig via cfe-dev]

I believe the interception works by taking over the CC and CXX environment variables, rather than with a preload.  This works fine for build systems that use those environment variables, and fails for others.

> -----Original Message-----
> From: cfe-dev <cfe-dev-bounces at lists.llvm.org> On Behalf Of ?????
> ???????? via cfe-dev
> Sent: Thursday, July 18, 2019 11:25 AM
> To: Arthur O'Dwyer <arthur.j.odwyer at gmail.com>
> Cc: cfe-dev <cfe-dev at lists.llvm.org>
> Subject: [EXTERNAL] Re: [cfe-dev] How does scan-build
> 
> Hello Arthur,
> 
> intercepting calls by scan-build, during it calls make or ninja, does make
> sense, to detect when clang is actually invoked.
> 
> But a possible way to call scan-build is with the form “scan-build >any-
> compiler< compile-options”.  The compiler could be clang, gcc or anything
> else.  How can a preloaded library intercept the execution of any compiler,
> but not for a non- compiler?
> 
> Regards
>   Дилян
> 
> On Thu, 2019-07-18 at 09:59 -0400, Arthur O'Dwyer wrote:
> > On Thu, Jul 18, 2019 at 5:54 AM Дилян Палаузов via cfe-dev <cfe-
> dev at lists.llvm.org> wrote:
> > > Hello,
> > >
> > > how does scan-build exactly parse its parameters?
> > >
> > > How does “scan-build make” know, that it should just invoke make and
> not do anything until a compiler is invoked.
> >
> > My understanding is that scan-build itself merely sets `LD_PRELOAD=some-
> library.so` for all processes spawned directly or indirectly from scan-build.
> Then it goes ahead and spawns a child process to run whatever command
> you gave it — e.g., `make`.
> > `make` will eventually spawn a child or grandchild process for `clang`. When
> that happens, `some-library.so` will notice and cause different behavior.
> Either it will tell `clang` to invoke the static analyzer, or it will write out "hey,
> clang is being called!" to an external trace log. This external trace log is what
> Christian and Paulo are calling a "compilation database." The trace can be
> used later to re-invoke the static analyzer for each file that was compiled
> during the build, without having to `make clean` the entire project.
> >
> > I confirmed some of my recollections via this documentation:
> > https://urldefense.com/v3/__https://github.com/rizsotto/scan-build__;!
> > fqWJcnlTkjM!98b-arsF7Aoim8t_p86Nq9t-
> fgh8eXtlxs2gZzrJMh4asXlphunNdbzsXe
> > p7$
> >
> > > Does “scan-build cc …” parse in fact the source code, or the
> > > generated object files and in the former case, is the compiler invoked or
> does scan-build just considers the parameters passed to the compiler?
> >
> > `scan-build` causes the static analyzer to be invoked. The static analyzer
> must parse the C++ source code. There is no way to "static-analyze" an
> object file.
> >
> > –Arthur
> 
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