[v4,4/4] lttng-babeltrace: add debug info support

Since Babeltrace 1.4, there is support for printing debug information
along with compatible traces and event records. Babeltrace needs
elfutils in this case. If elfutils can be built with the current
configuration, the lttng-babeltrace package selects it and builds
with support for debug information. Otherwise the menuconfig shows
a comment which explains why debug information support cannot be
built.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
---
Changes v3 -> v4:
  - Remove duplicate --disable-debug-info.
  - Replace patch to remove line in configure.ac with patch submitted
    upstream to add a cache variable to the elfutils check.
  - Use said cache variable in LTTNG_BABELTRACE_CONF_ENV.

 ...-m4-ax_lib_elfutils.m4-add-cache-variable.patch | 74 ++++++++++++++++++++++
 package/lttng-babeltrace/Config.in                 | 17 +++++
 package/lttng-babeltrace/lttng-babeltrace.mk       | 12 +++-
 3 files changed, 102 insertions(+), 1 deletion(-)
 create mode 100644 package/lttng-babeltrace/0002-m4-ax_lib_elfutils.m4-add-cache-variable.patch

Hello,

On Wed,  2 Nov 2016 02:55:08 -0400, Philippe Proulx wrote:

> diff --git a/package/lttng-babeltrace/0002-m4-ax_lib_elfutils.m4-add-cache-variable.patch b/package/lttng-babeltrace/0002-m4-ax_lib_elfutils.m4-add-cache-variable.patch
> new file mode 100644
> index 0000000..b592d7f
> --- /dev/null
> +++ b/package/lttng-babeltrace/0002-m4-ax_lib_elfutils.m4-add-cache-variable.patch
> @@ -0,0 +1,74 @@
> +From 697ab0905c59561562dc52cd3b925781e07814f3 Mon Sep 17 00:00:00 2001
> +From: Philippe Proulx <eeppeliteloop@gmail.com>
> +Date: Wed, 2 Nov 2016 01:40:12 -0400
> +Subject: [PATCH 1/3] m4/ax_lib_elfutils.m4: add cache variable

Please use git format-patch -N to generate the patches. I've fixed that
up manually.

> +

This patch really needed a better commit log, so I've added some
details here.

Essentially: an empty commit log for a non-trivial patch is always a
bug. And I believe this rule is not Buildroot specific.

> +if BR2_PACKAGE_LTTNG_BABELTRACE
> +
> +config BR2_PACKAGE_LTTNG_BABELTRACE_DEBUG_INFO
> +	bool
> +	default y
> +	depends on !BR2_bfin # elfutils
> +	depends on !BR2_STATIC_LIBS # elfutils
> +	depends on BR2_TOOLCHAIN_USES_UCLIBC || BR2_TOOLCHAIN_USES_GLIBC # elfutils
> +	select BR2_PACKAGE_ELFUTILS
> +
> +comment "handling debug info in traces needs a glibc or uClibc toolchain w/ dynamic library"
> +	depends on !BR2_bfin # elfutils
> +	depends on BR2_STATIC_LIBS \
> +		|| !(BR2_TOOLCHAIN_USES_UCLIBC || BR2_TOOLCHAIN_USES_GLIBC)
> +
> +endif

This stuff is really complicated, so I've instead removed the
sub-option, and simply made lttng-babeltrace.mk enable debug info
support when BR2_PACKAGE_ELFUTILS=y.

Thanks!

Thomas

On Wed, Nov 2, 2016 at 6:10 PM, Thomas Petazzoni
<thomas.petazzoni@free-electrons.com> wrote:
> Hello,
>
> On Wed,  2 Nov 2016 02:55:08 -0400, Philippe Proulx wrote:
>
>> diff --git a/package/lttng-babeltrace/0002-m4-ax_lib_elfutils.m4-add-cache-variable.patch b/package/lttng-babeltrace/0002-m4-ax_lib_elfutils.m4-add-cache-variable.patch
>> new file mode 100644
>> index 0000000..b592d7f
>> --- /dev/null
>> +++ b/package/lttng-babeltrace/0002-m4-ax_lib_elfutils.m4-add-cache-variable.patch
>> @@ -0,0 +1,74 @@
>> +From 697ab0905c59561562dc52cd3b925781e07814f3 Mon Sep 17 00:00:00 2001
>> +From: Philippe Proulx <eeppeliteloop@gmail.com>
>> +Date: Wed, 2 Nov 2016 01:40:12 -0400
>> +Subject: [PATCH 1/3] m4/ax_lib_elfutils.m4: add cache variable
>
> Please use git format-patch -N to generate the patches. I've fixed that
> up manually.

I always forget this, sorry.

>
>> +
>
> This patch really needed a better commit log, so I've added some
> details here.
>
> Essentially: an empty commit log for a non-trivial patch is always a
> bug. And I believe this rule is not Buildroot specific.
>
>> +if BR2_PACKAGE_LTTNG_BABELTRACE
>> +
>> +config BR2_PACKAGE_LTTNG_BABELTRACE_DEBUG_INFO
>> +     bool
>> +     default y
>> +     depends on !BR2_bfin # elfutils
>> +     depends on !BR2_STATIC_LIBS # elfutils
>> +     depends on BR2_TOOLCHAIN_USES_UCLIBC || BR2_TOOLCHAIN_USES_GLIBC # elfutils
>> +     select BR2_PACKAGE_ELFUTILS
>> +
>> +comment "handling debug info in traces needs a glibc or uClibc toolchain w/ dynamic library"
>> +     depends on !BR2_bfin # elfutils
>> +     depends on BR2_STATIC_LIBS \
>> +             || !(BR2_TOOLCHAIN_USES_UCLIBC || BR2_TOOLCHAIN_USES_GLIBC)
>> +
>> +endif
>
> This stuff is really complicated, so I've instead removed the
> sub-option, and simply made lttng-babeltrace.mk enable debug info
> support when BR2_PACKAGE_ELFUTILS=y.

But then, if BR2_PACKAGE_ELFUTILS=n, you don't know that you could have
debug info support in Babeltrace if BR2_PACKAGE_ELFUTILS=y.

Or maybe it's not the job of menuconfig to tell the available features.

Phil

>
> Thanks!
>
> Thomas
> --
> Thomas Petazzoni, CTO, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com

Hello,

On Wed, 2 Nov 2016 19:01:24 -0400, Philippe Proulx wrote:

> > This stuff is really complicated, so I've instead removed the
> > sub-option, and simply made lttng-babeltrace.mk enable debug info
> > support when BR2_PACKAGE_ELFUTILS=y.  
> 
> But then, if BR2_PACKAGE_ELFUTILS=n, you don't know that you could have
> debug info support in Babeltrace if BR2_PACKAGE_ELFUTILS=y.

We have such automatic dependencies in a large number of packages, we
simply can't add sub-options for each and every features. Since this
one is not necessarily trivial, I've added in the commit an additional
paragraph in the Config.in help text to hint the user about the need to
enable elfutils to get debug info support.

Best regards,

Thomas