btrfs-progs-v4.12: cross compiling

btrfs-progs-v4.12: cross compiling

[Hallo32]

Hello at all,

I'm new at this list. If the mail is not in line with your standards 
please inform me.

Since versions 4.12 btrfs-progs is complicated to cross compile for 
other systems.
The problem is, that this version includes mktables, which needs to be 
compiled for the host system and executed there for the creation of 
tables.c.

Are there any changes planed for the next version of btrfs-progs to make 
the cross compiling as simple as in the past? A included tables.c for 
example?

Best regards

Re: btrfs-progs-v4.12: cross compiling

[David Sterba]

On Mon, Aug 14, 2017 at 02:17:26PM +0200, Hallo32 wrote:
> Since versions 4.12 btrfs-progs is complicated to cross compile for 
> other systems.
> The problem is, that this version includes mktables, which needs to be 
> compiled for the host system and executed there for the creation of 
> tables.c.
> 
> Are there any changes planed for the next version of btrfs-progs to make 
> the cross compiling as simple as in the past? A included tables.c for 
> example?

Yes, keeping the generated tables.c around is fine. There's no reason it
needs to be generated each time during build. I'll fix that in 4.12.1.
Thanks for the report, cross-compilation should stay supported.

Re: btrfs-progs-v4.12: cross compiling

[Qu Wenruo]

On 2017年08月14日 20:17, Hallo32 wrote:
> Hello at all,
> 
> I'm new at this list. If the mail is not in line with your standards 
> please inform me.
> 
> Since versions 4.12 btrfs-progs is complicated to cross compile for 
> other systems.
> The problem is, that this version includes mktables, which needs to be 
> compiled for the host system and executed there for the creation of 
> tables.c.
> 
> Are there any changes planed for the next version of btrfs-progs to make 
> the cross compiling as simple as in the past? A included tables.c for 
> example?

Including tables.c seems quite crazy for me.
Just check how many lines tables.c has.

If we screw up any number of it, RAID6 is screwed up and we will never 
find the bug by reviewing the such meaningless numbers.

We could enhance the makefile to use host-cc to compile and execute mktable.
But it may make the makefile more complicated just for one file.
(Well, I just don't want to screw traditional Makefile/configure any more)

Another solution is to generate tables.c using scripts, other binary 
executable.
I'll try to port mktable to bash or python, which should solve the 
problem withouth further complicating makefile.
(And maybe I can update kernel too, but kernel has its host-cc and 
cross-cc already distinguished well, so it may not help much)

Thanks,
Qu

> 
> Best regards
> -- 
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: btrfs-progs-v4.12: cross compiling

[Qu Wenruo]

On 2017年08月14日 21:06, David Sterba wrote:
> On Mon, Aug 14, 2017 at 02:17:26PM +0200, Hallo32 wrote:
>> Since versions 4.12 btrfs-progs is complicated to cross compile for
>> other systems.
>> The problem is, that this version includes mktables, which needs to be
>> compiled for the host system and executed there for the creation of
>> tables.c.
>>
>> Are there any changes planed for the next version of btrfs-progs to make
>> the cross compiling as simple as in the past? A included tables.c for
>> example?
> 
> Yes, keeping the generated tables.c around is fine. There's no reason it
> needs to be generated each time during build. I'll fix that in 4.12.1.

But the number of lines and impossibility to review it makes it not 
suitable to be managed by git.

What about using script to generate it?

Thanks,
Qu

> Thanks for the report, cross-compilation should stay supported.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: btrfs-progs-v4.12: cross compiling

[David Sterba]

On Mon, Aug 14, 2017 at 09:17:08PM +0800, Qu Wenruo wrote:
> 
> 
> On 2017年08月14日 21:06, David Sterba wrote:
> > On Mon, Aug 14, 2017 at 02:17:26PM +0200, Hallo32 wrote:
> >> Since versions 4.12 btrfs-progs is complicated to cross compile for
> >> other systems.
> >> The problem is, that this version includes mktables, which needs to be
> >> compiled for the host system and executed there for the creation of
> >> tables.c.
> >>
> >> Are there any changes planed for the next version of btrfs-progs to make
> >> the cross compiling as simple as in the past? A included tables.c for
> >> example?
> > 
> > Yes, keeping the generated tables.c around is fine. There's no reason it
> > needs to be generated each time during build. I'll fix that in 4.12.1.
> 
> But the number of lines and impossibility to review it makes it not 
> suitable to be managed by git.

I don't understand your concern. The file is generated from a set of
formulas, not intended to be updated directly.
> 
> What about using script to generate it?

We do have the mktables utility to generate it and I'll regenerate it
should there be a change to kernel-lib/mktables.c

Re: btrfs-progs-v4.12: cross compiling

[Qu Wenruo]

On 2017年08月14日 22:03, David Sterba wrote:
> On Mon, Aug 14, 2017 at 09:17:08PM +0800, Qu Wenruo wrote:
>>
>>
>> On 2017年08月14日 21:06, David Sterba wrote:
>>> On Mon, Aug 14, 2017 at 02:17:26PM +0200, Hallo32 wrote:
>>>> Since versions 4.12 btrfs-progs is complicated to cross compile for
>>>> other systems.
>>>> The problem is, that this version includes mktables, which needs to be
>>>> compiled for the host system and executed there for the creation of
>>>> tables.c.
>>>>
>>>> Are there any changes planed for the next version of btrfs-progs to make
>>>> the cross compiling as simple as in the past? A included tables.c for
>>>> example?
>>>
>>> Yes, keeping the generated tables.c around is fine. There's no reason it
>>> needs to be generated each time during build. I'll fix that in 4.12.1.
>>
>> But the number of lines and impossibility to review it makes it not
>> suitable to be managed by git.
> 
> I don't understand your concern. The file is generated from a set of
> formulas, not intended to be updated directly.

Yes, it should never be updated directly, so it's generated by a less 
than 400 lines program, instead of a whole 10K+ lines file managed by git.

>>
>> What about using script to generate it?
> 
> We do have the mktables utility to generate it and I'll regenerate it
> should there be a change to kernel-lib/mktables.c

I mean to replace mktables.c with a script.
So no cross compiler problems at all, and even easier Makefile.
No dependence on "mktables" program.

Thanks,
Qu
> 

Re: btrfs-progs-v4.12: cross compiling

[David Sterba]

On Mon, Aug 14, 2017 at 10:14:42PM +0800, Qu Wenruo wrote:
> On 2017年08月14日 22:03, David Sterba wrote:
> > On Mon, Aug 14, 2017 at 09:17:08PM +0800, Qu Wenruo wrote:
> >> On 2017年08月14日 21:06, David Sterba wrote:
> >>> On Mon, Aug 14, 2017 at 02:17:26PM +0200, Hallo32 wrote:
> >>>> Since versions 4.12 btrfs-progs is complicated to cross compile for
> >>>> other systems.
> >>>> The problem is, that this version includes mktables, which needs to be
> >>>> compiled for the host system and executed there for the creation of
> >>>> tables.c.
> >>>>
> >>>> Are there any changes planed for the next version of btrfs-progs to make
> >>>> the cross compiling as simple as in the past? A included tables.c for
> >>>> example?
> >>>
> >>> Yes, keeping the generated tables.c around is fine. There's no reason it
> >>> needs to be generated each time during build. I'll fix that in 4.12.1.
> >>
> >> But the number of lines and impossibility to review it makes it not
> >> suitable to be managed by git.
> > 
> > I don't understand your concern. The file is generated from a set of
> > formulas, not intended to be updated directly.
> 
> Yes, it should never be updated directly, so it's generated by a less 
> than 400 lines program, instead of a whole 10K+ lines file managed by git.

mktables.c is synced from kernel sources, taking updates from there is
easier than porting any changes to the proposed scripted implementation.

The workflow is simple:
- copy kernel mktables.c changes to btrfs-progs mktables.c
- compile mktables
- run 'make kernel-lib/tables.c'
- commit the changes to git

All of that happens very rarely, if ever, the raid56 tables and
correction algorithms are set in stone. Any extensions need to be done
on both sides kernel/userspace.

> >> What about using script to generate it?
> > 
> > We do have the mktables utility to generate it and I'll regenerate it
> > should there be a change to kernel-lib/mktables.c
> 
> I mean to replace mktables.c with a script.
> So no cross compiler problems at all, and even easier Makefile.
> No dependence on "mktables" program.

Somebody has to implement the script and verify that the output is the
same, eventually sync changes. The cross-compilation should be fixed
with the pregenerated tables.c . Is Makefile size really a concern? The
number of related lines is like 7. I don't see any benefit in what you
propose and hopefully explained my viewpoint enough so I don't have to
continue.

Re: btrfs-progs-v4.12: cross compiling

[Goffredo Baroncelli]

On 08/14/2017 05:10 PM, David Sterba wrote:
> On Mon, Aug 14, 2017 at 10:14:42PM +0800, Qu Wenruo wrote:
[...]
> mktables.c is synced from kernel sources, taking updates from there is
> easier than porting any changes to the proposed scripted implementation.
> 
> The workflow is simple:
> - copy kernel mktables.c changes to btrfs-progs mktables.c

How the kernel deals with this kind of problem ? 
Looking at the source of btrfs Makefile, it is more simple to replace

  mktables: kernel-lib/mktables.c
        @echo "    [CC]     $@"
        $(Q)$(CC) $(CFLAGS) $< -o $@

with


  mktables: kernel-lib/mktables.c
        @echo "    [HOSTCC] $@"
        $(Q)$(HOSTCC) $(CFLAGS) $< -o $@

where HOSTCC is defined as

HOSTCC=gcc


(may be the same applied also to CFLAGS <-> HOSTCFLAGS ?)

> - compile mktables
> - run 'make kernel-lib/tables.c'
> - commit the changes to git
> 
> All of that happens very rarely, if ever, the raid56 tables and
> correction algorithms are set in stone. Any extensions need to be done
> on both sides kernel/userspace.
> 
>>>> What about using script to generate it?
>>>
>>> We do have the mktables utility to generate it and I'll regenerate it
>>> should there be a change to kernel-lib/mktables.c
>>
>> I mean to replace mktables.c with a script.
>> So no cross compiler problems at all, and even easier Makefile.
>> No dependence on "mktables" program.
> 
> Somebody has to implement the script and verify that the output is the
> same, eventually sync changes. The cross-compilation should be fixed
> with the pregenerated tables.c . Is Makefile size really a concern? The
> number of related lines is like 7. I don't see any benefit in what you
> propose and hopefully explained my viewpoint enough so I don't have to
> continue.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 


-- 
gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it>
Key fingerprint BBF5 1610 0B64 DAC6 5F7D  17B2 0EDA 9B37 8B82 E0B5

Re: btrfs-progs-v4.12: cross compiling

[Qu Wenruo]

On 2017年08月15日 02:57, Goffredo Baroncelli wrote:
> On 08/14/2017 05:10 PM, David Sterba wrote:
>> On Mon, Aug 14, 2017 at 10:14:42PM +0800, Qu Wenruo wrote:
> [...]
>> mktables.c is synced from kernel sources, taking updates from there is
>> easier than porting any changes to the proposed scripted implementation.
>>
>> The workflow is simple:
>> - copy kernel mktables.c changes to btrfs-progs mktables.c
> 
> How the kernel deals with this kind of problem ?
> Looking at the source of btrfs Makefile, it is more simple to replace
> 
>    mktables: kernel-lib/mktables.c
>          @echo "    [CC]     $@"
>          $(Q)$(CC) $(CFLAGS) $< -o $@
> 
> with
> 
> 
>    mktables: kernel-lib/mktables.c
>          @echo "    [HOSTCC] $@"
>          $(Q)$(HOSTCC) $(CFLAGS) $< -o $@
> 
> where HOSTCC is defined as
> 
> HOSTCC=gcc
> 
> 
> (may be the same applied also to CFLAGS <-> HOSTCFLAGS ?)

If using HOSTCC then I'm fine with it.

Thanks,
Qu

> 
>> - compile mktables
>> - run 'make kernel-lib/tables.c'
>> - commit the changes to git
>>
>> All of that happens very rarely, if ever, the raid56 tables and
>> correction algorithms are set in stone. Any extensions need to be done
>> on both sides kernel/userspace.
>>
>>>>> What about using script to generate it?
>>>>
>>>> We do have the mktables utility to generate it and I'll regenerate it
>>>> should there be a change to kernel-lib/mktables.c
>>>
>>> I mean to replace mktables.c with a script.
>>> So no cross compiler problems at all, and even easier Makefile.
>>> No dependence on "mktables" program.
>>
>> Somebody has to implement the script and verify that the output is the
>> same, eventually sync changes. The cross-compilation should be fixed
>> with the pregenerated tables.c . Is Makefile size really a concern? The
>> number of related lines is like 7. I don't see any benefit in what you
>> propose and hopefully explained my viewpoint enough so I don't have to
>> continue.
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
> 
> 

Re: btrfs-progs-v4.12: cross compiling

[Hallo32]

Am 15.08.2017 um 01:39 schrieb Qu Wenruo:
>
>
> On 2017年08月15日 02:57, Goffredo Baroncelli wrote:
>> On 08/14/2017 05:10 PM, David Sterba wrote:
>>> On Mon, Aug 14, 2017 at 10:14:42PM +0800, Qu Wenruo wrote:
>> [...]
>>> mktables.c is synced from kernel sources, taking updates from there is
>>> easier than porting any changes to the proposed scripted 
>>> implementation.
>>>
>>> The workflow is simple:
>>> - copy kernel mktables.c changes to btrfs-progs mktables.c
>>
>> How the kernel deals with this kind of problem ?
>> Looking at the source of btrfs Makefile, it is more simple to replace
>>
>>    mktables: kernel-lib/mktables.c
>>          @echo "    [CC]     $@"
>>          $(Q)$(CC) $(CFLAGS) $< -o $@
>>
>> with
>>
>>
>>    mktables: kernel-lib/mktables.c
>>          @echo "    [HOSTCC] $@"
>>          $(Q)$(HOSTCC) $(CFLAGS) $< -o $@
>>
>> where HOSTCC is defined as
>>
>> HOSTCC=gcc
>>
>>
>> (may be the same applied also to CFLAGS <-> HOSTCFLAGS ?)
>
> If using HOSTCC then I'm fine with it.
>
> Thanks,
> Qu

Hi,

CFLAGS needs also be replaced by something like HOSTCFLAGS, because if 
you use something like mips/architecture specific CFLAGS, they may be 
not applicably on the host system.

Best regards
>
>>
>>> - compile mktables
>>> - run 'make kernel-lib/tables.c'
>>> - commit the changes to git
>>>
>>> All of that happens very rarely, if ever, the raid56 tables and
>>> correction algorithms are set in stone. Any extensions need to be done
>>> on both sides kernel/userspace.
>>>
>>>>>> What about using script to generate it?
>>>>>
>>>>> We do have the mktables utility to generate it and I'll regenerate it
>>>>> should there be a change to kernel-lib/mktables.c
>>>>
>>>> I mean to replace mktables.c with a script.
>>>> So no cross compiler problems at all, and even easier Makefile.
>>>> No dependence on "mktables" program.
>>>
>>> Somebody has to implement the script and verify that the output is the
>>> same, eventually sync changes. The cross-compilation should be fixed
>>> with the pregenerated tables.c . Is Makefile size really a concern? The
>>> number of related lines is like 7. I don't see any benefit in what you
>>> propose and hopefully explained my viewpoint enough so I don't have to
>>> continue.
>>> -- 
>>> To unsubscribe from this list: send the line "unsubscribe 
>>> linux-btrfs" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>>
>>
>>
>

Re: btrfs-progs-v4.12: cross compiling

[David Sterba]

On Tue, Aug 15, 2017 at 02:44:07PM +0200, Hallo32 wrote:
> Am 15.08.2017 um 01:39 schrieb Qu Wenruo:
> > On 2017年08月15日 02:57, Goffredo Baroncelli wrote:
> >> On 08/14/2017 05:10 PM, David Sterba wrote:
> >>> On Mon, Aug 14, 2017 at 10:14:42PM +0800, Qu Wenruo wrote:
> >> [...]
> >>> mktables.c is synced from kernel sources, taking updates from there is
> >>> easier than porting any changes to the proposed scripted 
> >>> implementation.
> >>>
> >>> The workflow is simple:
> >>> - copy kernel mktables.c changes to btrfs-progs mktables.c
> >>
> >> How the kernel deals with this kind of problem ?
> >> Looking at the source of btrfs Makefile, it is more simple to replace
> >>
> >>    mktables: kernel-lib/mktables.c
> >>          @echo "    [CC]     $@"
> >>          $(Q)$(CC) $(CFLAGS) $< -o $@
> >>
> >> with
> >>
> >>
> >>    mktables: kernel-lib/mktables.c
> >>          @echo "    [HOSTCC] $@"
> >>          $(Q)$(HOSTCC) $(CFLAGS) $< -o $@
> >>
> >> where HOSTCC is defined as
> >>
> >> HOSTCC=gcc
> >>
> >>
> >> (may be the same applied also to CFLAGS <-> HOSTCFLAGS ?)
> >
> > If using HOSTCC then I'm fine with it.
> 
> CFLAGS needs also be replaced by something like HOSTCFLAGS, because if 
> you use something like mips/architecture specific CFLAGS, they may be 
> not applicably on the host system.

Good point. Without a regular/automated cross-compilation build testing
I think we could break it quite easily. I'm going to keep the
pregenerated file in git.

Re: btrfs-progs-v4.12: cross compiling

[Eric Sandeen]

On 8/15/17 7:48 AM, David Sterba wrote:
> On Tue, Aug 15, 2017 at 02:44:07PM +0200, Hallo32 wrote:

...

>>>> How the kernel deals with this kind of problem ?
>>>> Looking at the source of btrfs Makefile, it is more simple to replace
>>>>
>>>>    mktables: kernel-lib/mktables.c
>>>>          @echo "    [CC]     $@"
>>>>          $(Q)$(CC) $(CFLAGS) $< -o $@
>>>>
>>>> with
>>>>
>>>>
>>>>    mktables: kernel-lib/mktables.c
>>>>          @echo "    [HOSTCC] $@"
>>>>          $(Q)$(HOSTCC) $(CFLAGS) $< -o $@
>>>>
>>>> where HOSTCC is defined as
>>>>
>>>> HOSTCC=gcc
>>>>
>>>>
>>>> (may be the same applied also to CFLAGS <-> HOSTCFLAGS ?)
>>>
>>> If using HOSTCC then I'm fine with it.
>>
>> CFLAGS needs also be replaced by something like HOSTCFLAGS, because if 
>> you use something like mips/architecture specific CFLAGS, they may be 
>> not applicably on the host system.
> 
> Good point. Without a regular/automated cross-compilation build testing
> I think we could break it quite easily. I'm going to keep the
> pregenerated file in git.

Isn't using the host compiler for some binaries during a cross-compile
a very standard thing to do?

The kernel manages it, as shown above.  xfsprogs does it (see libxfs/Makefile
for the crc32table.h and crc32selftest targets), e2fsprogs does it (see
gen_crc32ctable target in lib/ext2fs/Makefile), etc.

Seems that checking in a generated file would be more prone to eventual
errors, no?

I guess it's harder to do in btrfs-progs since it's not using autotools...

-Eric

Re: btrfs-progs-v4.12: cross compiling

[Eric Sandeen]

On 8/15/17 12:28 PM, Eric Sandeen wrote:
> I guess it's harder to do in btrfs-progs since it's not using autotools...

Eh, I don't know why I thought that was still true :)  patch sent.

-Eric

Re: btrfs-progs-v4.12: cross compiling

[Jeff Mahoney]

[-- Attachment #1.1: Type: text/plain, Size: 1896 bytes --]

On 8/14/17 11:10 AM, David Sterba wrote:
> On Mon, Aug 14, 2017 at 10:14:42PM +0800, Qu Wenruo wrote:
>> On 2017年08月14日 22:03, David Sterba wrote:
>>> On Mon, Aug 14, 2017 at 09:17:08PM +0800, Qu Wenruo wrote:
>>>> On 2017年08月14日 21:06, David Sterba wrote:
>>>>> On Mon, Aug 14, 2017 at 02:17:26PM +0200, Hallo32 wrote:
>>>>>> Since versions 4.12 btrfs-progs is complicated to cross compile for
>>>>>> other systems.
>>>>>> The problem is, that this version includes mktables, which needs to be
>>>>>> compiled for the host system and executed there for the creation of
>>>>>> tables.c.
>>>>>>
>>>>>> Are there any changes planed for the next version of btrfs-progs to make
>>>>>> the cross compiling as simple as in the past? A included tables.c for
>>>>>> example?
>>>>>
>>>>> Yes, keeping the generated tables.c around is fine. There's no reason it
>>>>> needs to be generated each time during build. I'll fix that in 4.12.1.
>>>>
>>>> But the number of lines and impossibility to review it makes it not
>>>> suitable to be managed by git.
>>>
>>> I don't understand your concern. The file is generated from a set of
>>> formulas, not intended to be updated directly.
>>
>> Yes, it should never be updated directly, so it's generated by a less 
>> than 400 lines program, instead of a whole 10K+ lines file managed by git.
> 
> mktables.c is synced from kernel sources, taking updates from there is
> easier than porting any changes to the proposed scripted implementation.
> 
> The workflow is simple:
> - copy kernel mktables.c changes to btrfs-progs mktables.c
> - compile mktables
> - run 'make kernel-lib/tables.c'

Can't this happen as part of a make dist (that we don't do right now)?

> - commit the changes to git

... and anyone using the git repo directly can sort out how to build it?

-Jeff

-- 
Jeff Mahoney
SUSE Labs


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 819 bytes --]

Re: btrfs-progs-v4.12: cross compiling

[Qu Wenruo]

On 2017年08月16日 01:28, Eric Sandeen wrote:
> On 8/15/17 7:48 AM, David Sterba wrote:
>> On Tue, Aug 15, 2017 at 02:44:07PM +0200, Hallo32 wrote:
> 
> ...
> 
>>>>> How the kernel deals with this kind of problem ?
>>>>> Looking at the source of btrfs Makefile, it is more simple to replace
>>>>>
>>>>>     mktables: kernel-lib/mktables.c
>>>>>           @echo "    [CC]     $@"
>>>>>           $(Q)$(CC) $(CFLAGS) $< -o $@
>>>>>
>>>>> with
>>>>>
>>>>>
>>>>>     mktables: kernel-lib/mktables.c
>>>>>           @echo "    [HOSTCC] $@"
>>>>>           $(Q)$(HOSTCC) $(CFLAGS) $< -o $@
>>>>>
>>>>> where HOSTCC is defined as
>>>>>
>>>>> HOSTCC=gcc
>>>>>
>>>>>
>>>>> (may be the same applied also to CFLAGS <-> HOSTCFLAGS ?)
>>>>
>>>> If using HOSTCC then I'm fine with it.
>>>
>>> CFLAGS needs also be replaced by something like HOSTCFLAGS, because if
>>> you use something like mips/architecture specific CFLAGS, they may be
>>> not applicably on the host system.
>>
>> Good point. Without a regular/automated cross-compilation build testing
>> I think we could break it quite easily. I'm going to keep the
>> pregenerated file in git.
> 
> Isn't using the host compiler for some binaries during a cross-compile
> a very standard thing to do?
> 
> The kernel manages it, as shown above.  xfsprogs does it (see libxfs/Makefile
> for the crc32table.h and crc32selftest targets), e2fsprogs does it (see
> gen_crc32ctable target in lib/ext2fs/Makefile), etc.

Only if I can find it earlier.

> 
> Seems that checking in a generated file would be more prone to eventual
> errors, no?

Also my concern.

> 
> I guess it's harder to do in btrfs-progs since it's not using autotools...

And your patch does do a better job, especially for BUILD_CFLAGS and 
build cc detection.

Thanks,
Qu

> 
> -Eric
>