[PATCH v3 1/1] ARM: Thumb-2: Symbol manipulation macros for function body copying

[Jean Pihet]

On Thu, Jan 13, 2011 at 11:41 PM, Dave Martin <dave.martin at linaro.org> wrote:
> 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 and Nicolas Pitre for their input.
>
> Signed-off-by: Dave Martin <dave.martin at linaro.org>

Tested OK on OMAP3 in low power modes (RET/OFF) with !CONFIG_THUMB2_KERNEL.

Tested-by: Jean Pihet <j-pihet at ti.com>

> ---
> KernelVersion: v2.6.37
>
>  arch/arm/include/asm/fncpy.h |  110 ++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 110 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..6399265
> --- /dev/null
> +++ b/arch/arm/include/asm/fncpy.h
> @@ -0,0 +1,110 @@
> +/*
> + * 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((unsigned long)(dest_buf),   \
> +                       (unsigned long)(dest_buf) + (size));    \
> +                                                               \
> +               FSYM_REBASE(funcp, dest_buf);                   \
> +       })
> +
> +#endif /* !__ASM_FNCPY_H */
> --
> 1.7.1
>
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