It's not possible to build linux 32 bit on 64 bit host machine with gn

This fix adds possibility to provide path to directory containing sysroots for linux (32 bit and 64 bit). It's necessary if someone wants to make 32 bit build on 64 bit host with custom sysroot. Right now when custom sysroot is provided as gn parameter (target_sysroot) only 32 bit custom sysroot will be used. 64 bit sysroot (which is also needed by 32 bit build by - for example - protobuf) is expected to be found in default location.

BUG=622616

[ckulakowski, 2016-06-23 08:14:53]

Description was changed from

==========
It's not possible to build linux 32 bit on 64 bit host machine with gn

This fix contains two changes:
- set compiler flags based on target_cpu rather than on current_cpu
- don't look for sysroot in chromium path if it's provided as gn parameter

BUG=622616
==========

to

==========
It's not possible to build linux 32 bit on 64 bit host machine with gn

This fix contains two changes:
- set compiler flags based on target_cpu rather than on current_cpu
- don't look for sysroot in chromium path if it's provided as gn parameter

BUG=622616
==========

[ckulakowski, 2016-06-23 08:14:54]

ckulakowski@opera.com changed reviewers:
+ scottmg@chromium.org

[scottmg, 2016-06-23 16:16:43]

scottmg@chromium.org changed reviewers:
+ dpranke@chromium.org

[scottmg, 2016-06-23 16:16:44]

->Dirk

[Dirk Pranke, 2016-06-23 16:22:43]

I think these changes are wrong. What problems are you seeing?

We currently have a builder doing x86 builds that seems happy enough:

https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder%20%28dbg...

https://codereview.chromium.org/2091693002/diff/1/build/config/compiler/BUILD.gn
File build/config/compiler/BUILD.gn (right):

https://codereview.chromium.org/2091693002/diff/1/build/config/compiler/BUILD...
build/config/compiler/BUILD.gn:497: if (target_cpu == "x64") {
I think these changes are wrong and the existing code is correct; these changes
will (should?) break binaries built with the host toolchain.

https://codereview.chromium.org/2091693002/diff/1/build/config/sysroot.gni
File build/config/sysroot.gni (right):

https://codereview.chromium.org/2091693002/diff/1/build/config/sysroot.gni#ne...
build/config/sysroot.gni:17: if (target_sysroot != "") {
I think this probably has the same problem.

[ckulakowski, 2016-06-24 09:19:36]

On 2016/06/23 16:22:43, Dirk Pranke wrote:
> I think these changes are wrong. What problems are you seeing?
> 
> We currently have a builder doing x86 builds that seems happy enough:
> 
>
https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder%20%28dbg...
> 
>
https://codereview.chromium.org/2091693002/diff/1/build/config/compiler/BUILD.gn
> File build/config/compiler/BUILD.gn (right):
> 
>
https://codereview.chromium.org/2091693002/diff/1/build/config/compiler/BUILD...
> build/config/compiler/BUILD.gn:497: if (target_cpu == "x64") {
> I think these changes are wrong and the existing code is correct; these
changes
> will (should?) break binaries built with the host toolchain.
> 
> https://codereview.chromium.org/2091693002/diff/1/build/config/sysroot.gni
> File build/config/sysroot.gni (right):
> 
>
https://codereview.chromium.org/2091693002/diff/1/build/config/sysroot.gni#ne...
> build/config/sysroot.gni:17: if (target_sysroot != "") {
> I think this probably has the same problem.

Right now if you want to build chromium lin32 on 64 bit host machine with
use_sysroot=1 you must have
both sysroots: for lin32 and lin64 (you can check it by removing
build/linux/debian_wheezy_amd64-sysroot.
Project generation will fail then). In my opinion it's a bug in build system as
it shouldn't be required
to have 64 bit sysroot when you build 32 bit chromium. We don't download
sysroots by default in our
project so I could observe it.

[ckulakowski, 2016-06-24 12:51:12]

On 2016/06/24 09:19:36, ckulakowski wrote:
> On 2016/06/23 16:22:43, Dirk Pranke wrote:
> > I think these changes are wrong. What problems are you seeing?
> > 
> > We currently have a builder doing x86 builds that seems happy enough:
> > 
> >
>
https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder%20%28dbg...
> > 
> >
>
https://codereview.chromium.org/2091693002/diff/1/build/config/compiler/BUILD.gn
> > File build/config/compiler/BUILD.gn (right):
> > 
> >
>
https://codereview.chromium.org/2091693002/diff/1/build/config/compiler/BUILD...
> > build/config/compiler/BUILD.gn:497: if (target_cpu == "x64") {
> > I think these changes are wrong and the existing code is correct; these
> changes
> > will (should?) break binaries built with the host toolchain.
> > 
> > https://codereview.chromium.org/2091693002/diff/1/build/config/sysroot.gni
> > File build/config/sysroot.gni (right):
> > 
> >
>
https://codereview.chromium.org/2091693002/diff/1/build/config/sysroot.gni#ne...
> > build/config/sysroot.gni:17: if (target_sysroot != "") {
> > I think this probably has the same problem.
> 
> Right now if you want to build chromium lin32 on 64 bit host machine with
> use_sysroot=1 you must have
> both sysroots: for lin32 and lin64 (you can check it by removing
> build/linux/debian_wheezy_amd64-sysroot.
> Project generation will fail then). In my opinion it's a bug in build system
as
> it shouldn't be required
> to have 64 bit sysroot when you build 32 bit chromium. We don't download
> sysroots by default in our
> project so I could observe it.

I think I know the main cause for the problem. Right now when custom sysroot is
provided as gn parameter (target_sysroot) only 32 bit custom sysroot will be
used. 64 bit sysroot (which is also needed by 32 bit build by - for example - 
protobuf) is expected to be found in default location. I will prepare another
fix which adds possibility to provide path to directory containing both sysroots
for linux (32 bit and 64 bit). With this fix it will be possible to make build
which uses custom sysroots for 32 and 64 bit architecture.

[ckulakowski, 2016-06-24 14:38:59]

Description was changed from

==========
It's not possible to build linux 32 bit on 64 bit host machine with gn

This fix contains two changes:
- set compiler flags based on target_cpu rather than on current_cpu
- don't look for sysroot in chromium path if it's provided as gn parameter

BUG=622616
==========

to

==========
This fix adds possibility to provide path to directory containing sysroots for
linux (32 bit and 64 bit). It's necessary if someone wants to make 32 bit build
on 64 bit host with custom sysroot. Right now when custom sysroot is provided as
gn parameter (target_sysroot) only 32 bit custom sysroot will be used. 64 bit
sysroot (which is also needed by 32 bit build by - for example - protobuf) is
expected to be found in default location.

BUG=622616
==========

[Dirk Pranke, 2016-06-24 19:43:34]

Yup, that would do it. I expect the fix may be somewhat complicated, though, and
we might want to use this as an excuse to refactor some of this logic.

I'm not sure what the best way to do it off-hand would be, so feel free to have
a go at it and we can start there.

[ckulakowski, 2016-06-27 08:08:02]

On 2016/06/24 19:43:34, Dirk Pranke wrote:
> Yup, that would do it. I expect the fix may be somewhat complicated, though,
and
> we might want to use this as an excuse to refactor some of this logic.
> 
> I'm not sure what the best way to do it off-hand would be, so feel free to
have
> a go at it and we can start there.

Closed as I created new review: https://codereview.chromium.org/2096323002