Hi,
On Wed, Oct 3, 2012 at 4:06 PM, Tom Rini trini@ti.com wrote:
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
On 10/03/12 15:59, Graeme Russ wrote:
Hi Simon,
On Thu, Oct 4, 2012 at 7:44 AM, Graeme Russ graeme.russ@gmail.com wrote:
Hi Simon,
On Oct 4, 2012 6:58 AM, "Simon Glass" sjg@chromium.org wrote:
Hi Graeme,
On Wed, Oct 3, 2012 at 1:47 PM, Graeme Russ graeme.russ@gmail.com wrote:
Hi Simon,
On Oct 4, 2012 6:40 AM, "Simon Glass" sjg@chromium.org wrote:
Hi Tom,
On Wed, Oct 3, 2012 at 1:04 PM, Tom Rini trini@ti.com wrote: > -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 > > On 10/03/12 12:53, Simon Glass wrote: > >> On x86 machines gd is unfortunately a #define, so we >> should avoid using gd for anything. This patch changes >> uses of gd to bgd so that ext4fs can be used on x86. >> >> Signed-off-by: Simon Glass sjg@chromium.org > > Is there any way to change x86 to not be using a #define > for gd?
I wasn't brave enough to look hard at that, although Graeme is on copy and will know. It is actually using inline assembly to access this special variable.
Isn't 'gd' used by everyone (global data)? I fail to see how this ever worked.
Well only x86 uses a #define for it, so other archs cause no problem. It means that we can't use 'gd' as a symbol anywhere in U-Boot. I suppose the only sensible use is a structure member, as here.
Ah, I see - and I don't see a quick and easy way out. Let me look a bit deeper...
I remember now... commit 9e6c572ff03cda84c88663b23c7157d8b1f275ac explains why the #define gd came about:
"Use the base address of the 'F' segment as a pointer to the global data structure. By adding the linear address (i.e. the 'D' segment address) as the first word of the global data structure, the address of the global data relative to the 'D' segment can be found simply, for example, by:
fs movl 0, %eax
This makes the gd 'pointer' writable prior to relocation (by reloading the Global Desctriptor Table) which brings x86 into line with all other arches
NOTE: Writing to the gd 'pointer' is expensive (but we only do it twice) but using it to access global data members (read and write) is still fairly cheap"
The other option was rather ugly - create gd_get() and gd_set() inline functions and replace all instances of gd-> in all U-Boot source with gd_get()-> or gd_set(foo). I don't think it would have made any difference to code size, but the amount of code touched would have been massive.
The only other option I can think of is to change gd into something much less likely to be used as a symbol (__gd for example), but again, the patch to do so would be huge
I'm open to alternatives
OK, we'll just go with re-naming the ext4 part and build-testing things on x86 more often :) Thanks for digging up the details!
Sounds good, thank you both.
Regards Simon
Tom
-----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://www.enigmail.net/
iQIcBAEBAgAGBQJQbMTaAAoJENk4IS6UOR1WWmkP/2eRqqVTtCMwNZ6JP7W/lKDl bGu2PrIqufPdM2CnQJPpgWWT0PcBIV8thkw5DPhJovjkH7bjFc9bmjXjX6sNZU7V EnMxU/v6GUdCtM2QKeRv2x7a8iLj2uOcZS4tTg68vA7iD7fj5PwDBTNIGLCSh9EC VbDo2juPXjz+jSRvuhU7w0MzbeRhwdZ2yACZjlNbnX5TdWam1iXMnxlPPh/pC0Td ejwy0RuQwHPM7Gxy88b2wIc5DOXn8zoWrqLo1tx8B5S4b6jG+vI8zsFozi4lL9NJ iCinGd56xDNBIQKPr2NjdpSqkh01efpHqaa7tuBa5mzswNDQikoOXE/ncPFqW618 6kaAHfzCAmSQb/QbwV5576LWw2LcQPGDzz8Mb8iL03nAgHZI8an/blEdJjK6j+1G EpwzXQ6YkAWnrjCuAMGwfm/ARXai/Qh2YSnT5SPMxIXlWxIfAT7PsBRNbXOLQQp0 M/+NNE25cqAiZqwCxAT/eYR/huJtXbOqOj7GiH9NCn5L8c0Vm3mJ+o+YzRiraNro D2INZRE1B7347wxb/wkjHlLTfz219RrkSNJE7HBHGPbrtSQOXZaeTa44TZPwZbKP YuDojx9jMeuVQz1xqAoZECjdIgSEDjNcWcXU6l0JZYQClqDhxtS3GTdnlmMY0kdm kcZsmBCbojJchtN+VUp8 =0NwK -----END PGP SIGNATURE-----