[Buildroot] BR2_ENABLE_DEBUG is (incorrectly) using `Debug` for CMAKE_BUILD_TYPE instead of `RelWithDebInfo`

[Mehdi AMINI <joker.eph@gmail.com>]

2017-08-24 14:39 GMT-07:00 Arnout Vandecappelle <arnout@mind.be>:

>
>
> On 23-08-17 11:45, Mehdi AMINI wrote:
> [snip]
> > Two practical examples of packages that shows what can go wrong:
> >
> > 1) ceres-solver ( https://github.com/ceres-solver/ceres-solver )
> >
> > When configured with CMAKE_BUILD_TYPE=Release, it'll generate:
> >
> >     lib/libceres.a
> >
> > However with CMAKE_BUILD_TYPE=Debug we end up with:
> >
> >     lib/libceres-debug.a
> >
> >
> > 2) the LLVM compiler is doing special casing based on the value of
> > CMAKE_BUILD_TYPE. For example:
> >
> >     if (NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG" AND
> >         NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "RELWITHDEBINFO")
> >       add_flag_if_supported("-gline-tables-only" GLINE_TABLES_ONLY)
> >     endif()
> >     # Use -O1 even in debug mode, otherwise sanitizers slowdown is too
> large.
> >     if (uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
> >       add_flag_if_supported("-O1" O1)
> >     endif()
> >
> > Or also:
> >
> > if( NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG" )
> >   option(LLVM_ENABLE_ASSERTIONS "Enable assertions" OFF)
> > else()
> >   option(LLVM_ENABLE_ASSERTIONS "Enable assertions" ON)
> > endif()
> >
> >
> > In my experience it has been quite common for CMake projects to use
> > CMAKE_BUILD_TYPE to differentiate on more than just default optimization
> level.
>
>  I think this is exactly why we should use Debug/Release instead of always
> using
> Release: the CmakeLists.txt may enable some other things conditional on
> debug,
> and when you choose BR2_ENABLE_DEBUG, you typically want those other
> things.
> Like the assertions in LLVM.
>

This is not what the documentation / description of the option says I
believe. I wouldn't expect the generated code to be any different when
enabling BR2_ENABLE_DEBUG personally (other than the added DWARF section).
My reading of the description is that I should be able to turn it on and
the binaries in the target directory should be bit-to-bit identical
(assuming the rest of the build and the compiler is deterministic).

If that's not the intent behind BR2_ENABLE_DEBUG, it seems to me that
another option could be useful to provide exactly this mode: getting debug
info in the staging directory without affecting anything in the target.

Hope this makes sense.

Best,

-- 
Mehdi



>
>  The ceres solver is something else. That package is just doing the wrong
> thing.
> It needs to be patched to remove that -debug suffix. We do something
> similar for
> synergy, for instance.
>
>  Regards,
>  Arnout
>
>
> --
> Arnout Vandecappelle                          arnout at mind be
> Senior Embedded Software Architect            +32-16-286500
> Essensium/Mind                                http://www.mind.be
> G.Geenslaan 9, 3001 Leuven, Belgium           BE 872 984 063 RPR Leuven
> LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
> GPG fingerprint:  7493 020B C7E3 8618 8DEC 222C 82EB F404 F9AC 0DDF
>
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