[PATCH v3 2/4] asm-generic: Provide a fncpy() implementation

Florian Fainelli
2017-06-17T00:07:42Z

Define a generic fncpy() implementation largely based on the ARM version
that requires an 8 bytes alignment for the destination address where to
copy this function as well as the function's own address.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
include/asm-generic/fncpy.h | 93 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 93 insertions(+)
create mode 100644 include/asm-generic/fncpy.h

diff --git a/include/asm-generic/fncpy.h b/include/asm-generic/fncpy.h
new file mode 100644
index 000000000000..ec03b83b8535
--- /dev/null
+++ b/include/asm-generic/fncpy.h
@@ -0,0 +1,93 @@
+/*
+ * include/asm-generic/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.
+ *
+ * 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.
+ *
+ * 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);
+ *
+ * ... 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/bug.h>
+#include <asm/cacheflush.h>
+
+/*
+ * Minimum alignment requirement for the source and destination addresses
+ * for function copying.
+ */
+#define FNCPY_ALIGN 8
+
+#define fncpy(dest_buf, funcp, size) ({ \
+ uintptr_t __funcp_address; \
+ typeof(funcp) __result; \
+ \
+ asm("" : "=r" (__funcp_address) : "0" (funcp)); \
+ \
+ /* \
+ * Ensure alignment of source and destination addresses. \
+ */ \
+ BUG_ON((uintptr_t)(dest_buf) & (FNCPY_ALIGN - 1) || \
+ (__funcp_address & (FNCPY_ALIGN - 1))); \
+ \
+ memcpy(dest_buf, (void const *)__funcp_address, size); \
+ flush_icache_range((unsigned long)(dest_buf), \
+ (unsigned long)(dest_buf) + (size)); \
+ \
+ asm("" : "=r" (__result) \
+ : "0" ((uintptr_t)(dest_buf))); \
+ \
+ __result; \
+})
+
+#endif /* !__ASM_FNCPY_H */
--
2.9.3