Re: [PATCHv2 3/3] perf: add helper makefile for cross compiling libs

[Ingo Molnar <mingo@kernel.org>]

* Rabin Vincent <rabin.vincent@axis.com> wrote:

> It's easy to cross-compile a minimal perf binary without any external
> libraries (other than a C library of course).  But many useful features
> depend on external libraries, so to get them one needs to either
> cross-compile a bunch of libraries manually and send in the correct
> paths or integrate the perf build into some external build system.
> 
> In order to make it easier for people to qucikly get up and running with
> a fairly full featured cross-compiled mainline perf, provide a helper makefile
> which can be used to download and build the required libraries, which can then
> be used in a static build of perf.
> 
> For example, assuming an arm-linux-gcc cross-compiler is present in the
> PATH, the following is what one seens if one tries to build a static
> perf for ARM:
> 
>  $ make ARCH=arm CROSS_COMPILE=arm-linux- LDFLAGS="-static"
> 
>  Auto-detecting system features:
>  ...                         dwarf: [ OFF ]
>  ...                         glibc: [ on  ]
>  ...                          gtk2: [ OFF ]
>  ...                      libaudit: [ OFF ]
>  ...                        libbfd: [ OFF ]
>  ...                        libelf: [ OFF ]
>  ...                       libnuma: [ OFF ]
>  ...        numa_num_possible_cpus: [ OFF ]
>  ...                       libperl: [ OFF ]
>  ...                     libpython: [ OFF ]
>  ...                      libslang: [ OFF ]
>  ...                     libunwind: [ OFF ]
>  ...            libdw-dwarf-unwind: [ OFF ]
>  ...                          zlib: [ OFF ]
>  ...                          lzma: [ OFF ]
>  ...                     get_cpuid: [ OFF ]
> 
> By using the new Makefile.cross first, we get many important features:
> 
>  $ make ARCH=arm CROSS_COMPILE=arm-linux- -f Makefile.cross
>  $ make ARCH=arm CROSS_COMPILE=arm-linux- LDFLAGS="-static"
> 
>   Auto-detecting system features:
>   ...                         dwarf: [ on  ]
>   ...                         glibc: [ on  ]
>   ...                          gtk2: [ OFF ]
>   ...                      libaudit: [ on  ]
>   ...                        libbfd: [ on  ]
>   ...                        libelf: [ on  ]
>   ...                       libnuma: [ OFF ]
>   ...        numa_num_possible_cpus: [ OFF ]
>   ...                       libperl: [ OFF ]
>   ...                     libpython: [ OFF ]
>   ...                      libslang: [ on  ]
>   ...                     libunwind: [ on  ]
>   ...            libdw-dwarf-unwind: [ OFF ]
>   ...                          zlib: [ on  ]
>   ...                          lzma: [ on  ]
>   ...                     get_cpuid: [ OFF ]

That's really nice!

Would it be possible to add a gcc and glibc building portion as well? That would 
make it entirely self-hosting.

Something like:

    make ARCH=arm BOOTSTRAP=1

... would magically fetch everything needed, and (given enough Internet bandwidth 
and a fast enough machine) build a whole cross-environment from scratch.

Personally I'd even use this to bootstrap kernel cross-builds.

It could also be used to cross-build to the host architecture as well: it would 
make it easier to test perf on the latest GCC and glibc versions. (Which the host 
distribution does not carry.)

Thanks,

	Ingo