-----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! - -- 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
