[OE-core] Verification on how TARGET_CFLAGS is set

[Richard Purdie]

On Mon, 2015-03-30 at 15:37 -0500, Mark Hatle wrote:
> 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)

Are you sure its even that? I thought it was literally just the debug ID
code and the paths to debug were assumed by the debug tools which would
search several locations for a matching ID?

Cheers,

Richard