Dear Albert ARIBAUD,
In message 4CE0388E.2070601@free.fr you wrote:
Register use is documented in the top level README.
My bad: I'd missed that one because I always go straight to the doc/ directory for documentation of this kind -- the root README I never read apart from the first few pages, and I would not have thought it to give this level of detail.
;-)
BTW, a fix to this ./README is in order as GOT is not used any more with ELF ARM relocation, so r9 is not needed for this anymore...
Agreed.
... and even though I don't like the idea of reserving a register for gd, since we must for the moment, then using the (now available) r9 register would be *more* 'EABI/AAPCS-compliant' than using r8 (as I said, one could think of this use of r9 as 'our AAPCS variant').
Actually situation might be differenton ARM. I just did quick and ditry test for the TX25 board:
diff --git a/arch/arm/cpu/arm926ejs/config.mk b/arch/arm/cpu/arm926ejs/config.mk index f8ef90f..f8bbeba 100644 --- a/arch/arm/cpu/arm926ejs/config.mk +++ b/arch/arm/cpu/arm926ejs/config.mk @@ -21,7 +21,7 @@ # MA 02111-1307 USA #
-PLATFORM_RELFLAGS += -fno-common -ffixed-r8 -msoft-float +PLATFORM_RELFLAGS += -fno-common -msoft-float
PLATFORM_CPPFLAGS += -march=armv5te # ========================================================================= diff --git a/arch/arm/include/asm/global_data.h b/arch/arm/include/asm/global_data.h index ada3fbb..7561523 100644 --- a/arch/arm/include/asm/global_data.h +++ b/arch/arm/include/asm/global_data.h @@ -86,6 +86,13 @@ typedef struct global_data { #define GD_FLG_DISABLE_CONSOLE 0x00040 /* Disable console (in & out) */ #define GD_FLG_ENV_READY 0x00080 /* Environment imported into hash table */
+ +#if 0 #define DECLARE_GLOBAL_DATA_PTR register volatile gd_t *gd asm ("r8") +#else /* We could use plain global data, but the resulting code is bigger */ +#define XTRN_DECLARE_GLOBAL_DATA_PTR extern +#define DECLARE_GLOBAL_DATA_PTR XTRN_DECLARE_GLOBAL_DATA_PTR \ + gd_t *gd +#endif
#endif /* __ASM_GBL_DATA_H */ diff --git a/arch/arm/lib/board.c b/arch/arm/lib/board.c index 1fd5f83..b0de6c7 100644 --- a/arch/arm/lib/board.c +++ b/arch/arm/lib/board.c @@ -647,3 +647,14 @@ void hang (void) puts ("### ERROR ### Please RESET the board ###\n"); for (;;); } + +#if 1 /* We could use plain global data, but the resulting code is bigger */ +/* + * Pointer to initial global data area + * + * Here we initialize it. + */ +#undef XTRN_DECLARE_GLOBAL_DATA_PTR +#define XTRN_DECLARE_GLOBAL_DATA_PTR /* empty = allocate here */ +DECLARE_GLOBAL_DATA_PTR = (gd_t *) (CONFIG_SYS_INIT_SP_ADDR); +#endif /* 0 */
Compare sizes for "tx25":
text data bss dec hex filename 158730 8668 37120 204518 31ee6 ./u-boot with register 158574 8672 37120 204366 31e4e ./u-boot with global pointer
The global pointer method saves a total of 152 bytes here (156 in .text saved, but 4 in .data needed).
OK, this is not even 0.1% of the size, but anyway...
Best regards,
Wolfgang Denk