In low-level board support code, there is sometimes a need to copy a function body to another location at run-time. A straightforward call to memcpy doesn't work in Thumb-2, because bit 0 of external Thumb function symbols is set to 1, indicating that the function is Thumb. Without corrective measures, this will cause an off-by-one copy, and the copy may be called using the wrong instruction set. This patch adds macros to help with such cases. Particular care is needed, because C doesn't guarantee any defined behaviour when casting a function pointer to any other type. This has been observed to lead to strange optimisation side-effects when doing the arithmetic which is required in order to copy/move function bodies correctly in Thumb-2. Thanks to Russell King for his input on this patch. Signed-off-by: Dave Martin <dave.martin@xxxxxxxxxx> --- KernelVersion: v2.6.37 arch/arm/include/asm/fncpy.h | 111 ++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 111 insertions(+), 0 deletions(-) create mode 100644 arch/arm/include/asm/fncpy.h diff --git a/arch/arm/include/asm/fncpy.h b/arch/arm/include/asm/fncpy.h new file mode 100644 index 0000000..a155fb7 --- /dev/null +++ b/arch/arm/include/asm/fncpy.h @@ -0,0 +1,111 @@ +/* + * arch/arm/include/asm/fncpy.h - helper macros for function body copying + * + * Copyright (C) 2011 Linaro Limited + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ + +/* + * These macros are intended for use when there is a need to copy a low-level + * function body into special memory. + * + * For example, when reconfiguring the SDRAM controller, the code doing the + * reconfiguration may need to run from SRAM. + * + * NOTE: that the copied function body must be entirely self-contained and + * position-independent in order for this to work properly. + * + * + * Typical usage example: + * + * extern int f(args); + * extern uint32_t size_of_f; + * int (*copied_f)(args); + * void *sram_buffer; + * + * copied_f = fncpy(sram_buffer, &f, size_of_f); + * + * ... do any required D-side/I-side synchronisation ... + * + * ... later, call the function: ... + * + * copied_f(args); + * + * The size of the function to be copied can't be determined from C: + * this must be determined by other means, such as adding assmbler directives + * in the file where f is defined. + */ + + */ + +#ifndef __ASM_FNCPY_H +#define __ASM_FNCPY_H + +#include <linux/types.h> +#include <linux/string.h> + +#include <asm/cacheflush.h> + +/* Function pointer casting macros */ + +/* Cast function pointer to integer: */ +#define __funcp_to_uint(funcp) ({ \ + uintptr_t __result; \ + \ + asm("" : "=r" (__result) : "0" (funcp)); \ + __result; \ + }) + +/* Cast integer to function pointer with type matching funcp: */ +#define __uint_to_funcp(i, funcp) ({ \ + typeof(funcp) __result; \ + \ + asm("" : "=r" (__result) : "0" (i)); \ + __result; \ + }) + + +/* Function symbol manipulation macros */ + +/* + * FSYM_REBASE: Determine the correct function pointer for funcp, + * after the function has been copied to dest_buf: + */ +#define FSYM_REBASE(funcp, dest_buf) \ + __uint_to_funcp((uintptr_t)(dest_buf) | FSYM_TYPE(funcp), funcp) + +/* + * FSYM_BASE: Determine the base address in memory of the function funcp + * FSYM_TYPE: Determine the instruction set type (ARM/Thumb) of funcp + * (both defined below) + */ + +#ifdef CONFIG_THUMB2_KERNEL +#define FSYM_BASE(funcp) ((void *)(__funcp_to_uint(funcp) & ~(uintptr_t)1)) +#define FSYM_TYPE(funcp) (__funcp_to_uint(funcp) & 1) +#else /* !CONFIG_THUMB2_KERNEL */ +#define FSYM_BASE(funcp) ((void *)__funcp_to_uint(funcp)) +#define FSYM_TYPE(funcp) 0 +#endif /* !CONFIG_THUMB2_KERNEL */ + +/* Function copy helper */ +#define fncpy(dest_buf, funcp, size) ({ \ + memcpy(dest_buf, FSYM_BASE(funcp), size); \ + flush_icache_range(dest_buf, (char *)(dest_buf) + size); \ + \ + FSYM_REBASE(funcp, dest_buf); \ + }) + +#endif /* !__ASM_FNCPY_H */ -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html