[OE-core] Verification on how TARGET_CFLAGS is set

[Mark Hatle]

On 3/30/15 3:27 PM, Richard Purdie wrote:
> On Mon, 2015-03-30 at 13:09 +0000, Bryan Evenson wrote:
>> I am about to upgrade to the dizzy branch.  I have a built a bootable
>> image on my test build machine, and now I'm going to be applying
>> changes to the system I use for building production images.  I'm
>> planning on deleting my tmp directory to force a re-build of
>> everything.  Since I'm rebuilding everything anyway, I'm taking a
>> deeper look at the CFLAGS related settings and I'm getting a little
>> lost in the logic.  I'd like to verify these settings before I start
>> rebuilding everything.
>>
>> If I'm following the default logic correctly in bitbake.conf, by
>> default TARGET_CFLAGS will be set to "-O2 -pipe -g
>> -feliminate-unused-debug-types".  I want the default TARGET_CFLAGS for
>> my production image to be "-O2 -pipe".  What's the suggested variable
>> to change, and where, to get this final value?  Do I set TARGET_CFLAGS
>> directly, or do I set SELECTED_OPTIMIZATIONS or even
>> FULL_OPTIMIZATIONS?  Do I set it in local.conf or should I be setting
>> it somewhere else?
> 
> If I remember rightly, you need the -g option there to generate the -dbg
> packages correctly. The target system binaries won't change since we
> separate out the debug data into separate files as part of the packaging
> process.
> 
> You therefore can gain some build performance from turning that off but
> your runtime won't alter much (other than the debuglink ID which is a
> few bytes).

I strongly caution people against removing '-g' from their production builds.
If you do, you will no longer have any way to do any type of production/field
debug.  As Richard indicated the -g will cause the symbols and debug information
to get separated into special -dbg packages that you generally don't distribute
on a production device -- but those same -dbg package (preserved) can be later
used for debugging of production devices.

This is why the default is what it is.

The difference in executable size between -g (split debug) and w/o -g, is
usually around 15 - 30 bytes.  Roughly the length of the path to the executable
and/or library plus ".debug/" (7 characters)

--Mark

> Cheers,
> 
> Richard
>