Hi, On Wed, Oct 3, 2012 at 4:06 PM, Tom Rini <tr...@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.r...@gmail.com> wrote: >>> Hi Simon, >>> >>> On Oct 4, 2012 6:58 AM, "Simon Glass" <s...@chromium.org> wrote: >>>> >>>> Hi Graeme, >>>> >>>> On Wed, Oct 3, 2012 at 1:47 PM, Graeme Russ >>>> <graeme.r...@gmail.com> wrote: >>>>> Hi Simon, >>>>> >>>>> On Oct 4, 2012 6:40 AM, "Simon Glass" <s...@chromium.org> >>>>> wrote: >>>>>> >>>>>> Hi Tom, >>>>>> >>>>>> On Wed, Oct 3, 2012 at 1:04 PM, Tom Rini <tr...@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 <s...@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----- _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
