Re: [PATCH] Enable download and build of expat when cross-static gdb is requested

["Yann E. MORIN" <yann dot morin dot 1998 at free dot fr>]

Daniel, Bryan, All,

On 2013-06-06 22:16 -0700, Daniel Price spake thusly:
> On Thu, Jun 6, 2013 at 6:58 PM, Bryan Hundven <bryanhundven@gmail.com> wrote:
> ...
> >
> > (See note after the next note)
> >
> >>+            do_gdb_expat_backend host=""               \
> >
> > Shouldn't host="${CT_TARGET}" ?

This is expat for cross-gdb, not native gdb. So it's not CT_TARGET, but
CT_HOST.

> I set it to "" so that we'd build expat for the system we're building on...

Since we're talking about expat for the cross-gdb, this is wrong. The
toolchain may run on a system different from the system it was built on.
Think canadian builds, for example, where:
  - toolchain is built on system A          (eg. an x86)
  - toolchian runs on system B              (eg. an PowerPC)
  - toolchain generates code for system C   (eg. an ARM)

In this case, you don't want to build expat for system A, but for
system B.

<rant>
Sliding a bit on this topic, we could consider a canadian build to be
the norm for a toolchain, and all other cases to be denormalised cases;
for example, a cross-toolchain is just a canadian toolchain where
build == host; a cross-native another special case where host == target; 
and a native where build == host == target.

The fact that a canadian is more complex is just because it is not
common (nowadays at least, it used to be more common long ago), and that
native is the norm, cross is a slightly denormalised native, cross-
native a relatively rare event, and canadian an exceptionally rare
occurence.

Life is life, we have to live it. ;-)
</rant>

> >>+                prefix="${CT_BUILD_DIR}/static-cross" \
> >
> > Since this build of expat is the same build as what is built for the
> > native gdb, we should save some time and set the prefix to
> > "${CT_BUILD_DIR}/static-target" and pushd to
> > "${CT_BUILD_DIR}/build-ncurses-target-${CT_TARGET}".
> > Then during native, in the same code section, before building expat, we
> > could just check to see if it exists there and skip or build if it isn't.
> > Just an idea ;) (cross-gdb builds before native-gdb, if you are building
> > both)
> 
> Hi Bryan, thanks for the response--
> 
> Hmm.  Now I'm worried that I don't understand the problem I set out to
> solve :)  I thought that "native gdb" meant "a gdb cross-compiled to
> run on the target."

Right.

> Whereas I thought that cross-gdb meant "a gdb
> compiled to run on this host, targetted at a remote target."

Mostly. It's not "this host" but simply "the host" (see above, canadian
builds).

>  So for
> the first, we need a cross-compiled expat,

Right, and we already have it.

> and for the second we need
> one which is compiled for the (for lack of a better term) "host"
> system.

Right.

>  I'm confused as to why we could reuse the same build of
> expat?  Maybe I've missed something major here.  Thanks again,

I think you got it right in your explanations. But since you missed the
canadian build case, you missed that build != host in some cases.

Regards,
Yann E. MORIN.

PS. Sorry for the delay in anserwing these days, I've a hard time
finding enough time to handle real life, then do some computer-related
things afterwards... :-/
YEM.

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