Applied to:
git://git.denx.de/u-boot-nios.git next
Thanks,
--Scott
Thomas Chou wrote:
> The "-ffixed-r15" option doesn't work well for gcc4. Since we
> don't use gp for small data with option "-G0", we can use gp
> as global data pointer. This allows compiler to use r15. It
> is necessary for gcc4 to work properly.
>
> Signed-off-by: Thomas Chou <tho...@wytron.com.tw>
> ---
> v2: update standalone stubs and doc.
>
> README | 8 ++++++++
> arch/nios2/config.mk | 2 +-
> arch/nios2/cpu/start.S | 7 -------
> arch/nios2/include/asm/global_data.h | 2 +-
> doc/README.standalone | 13 +++++++------
> examples/standalone/stubs.c | 6 +++---
> 6 files changed, 20 insertions(+), 18 deletions(-)
>
> diff --git a/README b/README
> index 81692c0..acb3308 100644
> --- a/README
> +++ b/README
> @@ -4023,6 +4023,14 @@ On ARM, the following registers are used:
>
> ==> U-Boot will use R8 to hold a pointer to the global data
>
> +On Nios II, the ABI is documented here:
> + http://www.altera.com/literature/hb/nios2/n2cpu_nii51016.pdf
> +
> + ==> U-Boot will use gp to hold a pointer to the global data
> +
> + Note: on Nios II, we give "-G0" option to gcc and don't use gp
> + to access small data sections, so gp is free.
> +
> NOTE: DECLARE_GLOBAL_DATA_PTR must be used with file-global scope,
> or current versions of GCC may "optimize" the code too much.
>
> diff --git a/arch/nios2/config.mk b/arch/nios2/config.mk
> index 8e5d6ef..6789038 100644
> --- a/arch/nios2/config.mk
> +++ b/arch/nios2/config.mk
> @@ -27,6 +27,6 @@ CROSS_COMPILE ?= nios2-elf-
> STANDALONE_LOAD_ADDR = 0x02000000 -L $(gcclibdir)
>
> PLATFORM_CPPFLAGS += -DCONFIG_NIOS2 -D__NIOS2__
> -PLATFORM_CPPFLAGS += -ffixed-r15 -G0
> +PLATFORM_CPPFLAGS += -G0
>
> LDSCRIPT ?= $(SRCTREE)/$(CPUDIR)/u-boot.lds
> diff --git a/arch/nios2/cpu/start.S b/arch/nios2/cpu/start.S
> index d1016ea..76d3b52 100644
> --- a/arch/nios2/cpu/start.S
> +++ b/arch/nios2/cpu/start.S
> @@ -113,13 +113,6 @@ _cur: movhi r5, %hi(_cur - _start)
> bne r5, r6, 4b
> 5:
>
> - /* GLOBAL POINTER -- the global pointer is used to reference
> - * "small data" (see -G switch). The linker script must
> - * provide the gp address.
> - */
> - movhi gp, %hi(_gp)
> - ori gp, gp, %lo(_gp)
> -
> /* JUMP TO RELOC ADDR */
> movhi r4, %hi(_reloc)
> ori r4, r4, %lo(_reloc)
> diff --git a/arch/nios2/include/asm/global_data.h
> b/arch/nios2/include/asm/global_data.h
> index 34aa962..f1b3482 100644
> --- a/arch/nios2/include/asm/global_data.h
> +++ b/arch/nios2/include/asm/global_data.h
> @@ -48,6 +48,6 @@ typedef struct global_data {
> #define GD_FLG_LOGINIT 0x00020 /* Log Buffer has been
> initialized */
> #define GD_FLG_DISABLE_CONSOLE 0x00040 /* Disable console (in
> & out) */
>
> -#define DECLARE_GLOBAL_DATA_PTR register gd_t *gd asm ("r15")
> +#define DECLARE_GLOBAL_DATA_PTR register gd_t *gd asm ("gp")
>
> #endif /* __ASM_NIOS2_GLOBALDATA_H_ */
> diff --git a/doc/README.standalone b/doc/README.standalone
> index 885c92f..6381087 100644
> --- a/doc/README.standalone
> +++ b/doc/README.standalone
> @@ -19,12 +19,12 @@ Design Notes on Exporting U-Boot Functions to Standalone
> Applications:
> thus the compiler cannot perform type checks on these assignments.
>
> 2. The pointer to the jump table is passed to the application in a
> - machine-dependent way. PowerPC, ARM, MIPS and Blackfin architectures
> - use a dedicated register to hold the pointer to the 'global_data'
> - structure: r2 on PowerPC, r8 on ARM, k0 on MIPS, and P3 on Blackfin.
> - The x86 architecture does not use such a register; instead, the
> - pointer to the 'global_data' structure is passed as 'argv[-1]'
> - pointer.
> + machine-dependent way. PowerPC, ARM, MIPS, Blackfin and Nios II
> + architectures use a dedicated register to hold the pointer to the
> + 'global_data' structure: r2 on PowerPC, r8 on ARM, k0 on MIPS,
> + P3 on Blackfin and gp on Nios II. The x86 architecture does not
> + use such a register; instead, the pointer to the 'global_data'
> + structure is passed as 'argv[-1]' pointer.
>
> The application can access the 'global_data' structure in the same
> way as U-Boot does:
> @@ -56,6 +56,7 @@ Design Notes on Exporting U-Boot Functions to Standalone
> Applications:
> ARM 0x0c100000 0x0c100000
> MIPS 0x80200000 0x80200000
> Blackfin 0x00001000 0x00001000
> + Nios II 0x02000000 0x02000000
>
> For example, the "hello world" application may be loaded and
> executed on a PowerPC board with the following commands:
> diff --git a/examples/standalone/stubs.c b/examples/standalone/stubs.c
> index ce3371d..0187708 100644
> --- a/examples/standalone/stubs.c
> +++ b/examples/standalone/stubs.c
> @@ -84,7 +84,7 @@ gd_t *global_data;
> : : "i"(offsetof(gd_t, jt)), "i"(XF_ ## x) : "r0");
> #elif defined(CONFIG_NIOS2)
> /*
> - * r15 holds the pointer to the global_data, r8 is call-clobbered
> + * gp holds the pointer to the global_data, r8 is call-clobbered
> */
> #define EXPORT_FUNC(x) \
> asm volatile ( \
> @@ -92,11 +92,11 @@ gd_t *global_data;
> #x ":\n" \
> " movhi r8, %%hi(%0)\n" \
> " ori r8, r0, %%lo(%0)\n" \
> -" add r8, r8, r15\n" \
> +" add r8, r8, gp\n" \
> " ldw r8, 0(r8)\n" \
> " ldw r8, %1(r8)\n" \
> " jmp r8\n" \
> - : : "i"(offsetof(gd_t, jt)), "i"(XF_ ## x * sizeof(void *)) : "r15");
> + : : "i"(offsetof(gd_t, jt)), "i"(XF_ ## x * sizeof(void *)) : "gp");
> #elif defined(CONFIG_M68K)
> /*
> * d7 holds the pointer to the global_data, a0 is a call-clobbered
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