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nios2: fix r15 issue for gcc4

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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 <thomas@wytron.com.tw>
Signed-off-by: Scott McNutt <smcnutt@psyent.com>
This commit is contained in:
Thomas Chou 2010-05-21 11:08:03 +08:00 • committed by Scott McNutt
parent 661ba14051
commit 0df01fd3d7
6 changed files with 20 additions and 18 deletions
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8
README
View file

@ -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.

2
arch/nios2/config.mk
View file

@ -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

7
arch/nios2/cpu/start.S
View file

@ -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)

2
arch/nios2/include/asm/global_data.h
View file

@ -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_ */

13
doc/README.standalone
View file

@ -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:

6
examples/standalone/stubs.c
View file

@ -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