Dear Albert, Am Mi 21 Sep 2011 14:03:09 CEST schrieb Albert ARIBAUD: > Le 21/09/2011 13:20, Andreas Bießmann a écrit : >> Dear "GROYER, Anthony", >> Dear Albert, >> >> Am Mi 21 Sep 2011 12:51:33 CEST schrieb Albert ARIBAUD: >>> Le 21/09/2011 11:29, GROYER, Anthony a écrit : >>> >> >> <snip> >> >>> 3) replace use of r9-r10 with e.g. r10-r11 in the copy loop, to >>> preserve >>> r9 during relocation. >> >> If one is changing this place I would like to discuss another point >> here. >> In my last changeset for relocation I found some implementation in >> a/a/c/pxa/start.S which do save the register to stack before copy_loop, >> use almost all registers (only r8 is not used which is gd_t for arm, but >> I think it could be used here too cause it is saved on the stack) and >> save the registers back later on. >> I guess this could fasten the copy_loop a bit but needs to be proven. >> Anthony, if you change all start.S could you consider this also? > > I am not 100% sure I get your point, but I assume that you are asking > for *removal* of the saving and restoring, right?
No, that was not the point. I think the 'save registers before copy_loop to use more registers for ldmia/stmia instructions' is a good solution which could improve the copy_loop for all arm implementations. > I would tend to > agree that saving and restoring registers in relocate_code is moot, as > this function does not return in the usual sense. No the code does register save before copy_loop and restore them right afterwards. Therefore even r8 could be used in the copy_loop cause it is preserved on the (newly created) stack. Have a look at a/a/c/pxa/start.S from line 241 (relocate_code) to 263 (end of copy_loop). But I guess the ldmia/stmia instructions could even use r3-r11, only r0-r2 needs to be preserved for loop counting. I wonder if this could improve the copy_loop ... will try to test it these days, if no one else can do it (Anthony?). > As for r8, it should be preserved as it points to gd, but that is > ensured by the C code already IIRC. We use -ffixed-r8 therefore the compiler takes care for the C part, but we need to respect this in asm. Well, if we preserve r8 for the copy_loop and restore it right afterwards we could use it in the copy_loop for copy purposes. Cause there is no dereferencing of r8 in copy_loop. best regards Andreas Bießmann _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
