[PATCH v4] ARM: Thumb-2: Symbol manipulation macros for function body copying

On Mon, Jan 17, 2011 at 03:02:20PM +0100, Jean Pihet wrote:

On Fri, Jan 14, 2011 at 10:17 PM, Dave Martin [off-list ref] wrote:

quoted

+ * 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.
+ *
+ * NOTE: in order for embedded literals and data to get referenced correctly,
+ * the alignment of functions must be preserved when copying. ?To ensure this,
+ * the source and destination addresses for fncpy() must be aligned to a
+ * multiple of 8 bytes: you will be get a BUG() if this condition is not met.
+ * You will typically need a ".align 3" directive in the assembler where the
+ * function to be copied is defined, and ensure that your allocator for the
+ * destination buffer returns 8-byte-aligned pointers.

Note that aligning the source and destination pointers to a multiple
of 8 bytes has an impact on the behavio(u)r and so must be carefully
thought and tested on OMAP1/2/3 platforms.

OMAP3 is ARMv7, so is EABI.  EABI requires 64-bit data to be aligned to
natural 64-bit boundaries, so architecturally it's correct.

Nevertheless, the code may not be using 64-bit data, so that doesn't
apply - but fncpy() can't know that.