From 11738cf01f150afae913b88fb68675a272803d63 Mon Sep 17 00:00:00 2001 From: David Gibson Date: Mon, 19 Nov 2018 16:36:15 +1100 Subject: [PATCH] libfdt: Don't use memcpy to handle unaligned reads on ARM 6dcb8ba4 "libfdt: Add helpers for accessing unaligned words" introduced the fdt32_ld() and fdt64_ld() helpers for loading values from the FDT blob which might not be naturally aligned. This matters for ARM, where attempting a plain unaligned load will often cause an exception. However, it seems the memcpy() we used here was surprisingly expensive, making libfdt nearly 6x slower on at least some ARM platforms. This patch takes an alternative approach, using a bunch of 1-byte loads and shifts to implement the helpers. Signed-off-by: David Gibson --- libfdt/libfdt.h | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) diff --git a/libfdt/libfdt.h b/libfdt/libfdt.h index face02c..fdaa3e6 100644 --- a/libfdt/libfdt.h +++ b/libfdt/libfdt.h @@ -163,18 +163,26 @@ uint32_t fdt_next_tag(const void *fdt, int offset, int *nextoffset); static inline uint32_t fdt32_ld(const fdt32_t *p) { - fdt32_t v; + const uint8_t *bp = (const uint8_t *)p; - memcpy(&v, p, sizeof(v)); - return fdt32_to_cpu(v); + return ((uint32_t)bp[0] << 24) + | ((uint32_t)bp[1] << 16) + | ((uint32_t)bp[2] << 8) + | bp[3]; } static inline uint64_t fdt64_ld(const fdt64_t *p) { - fdt64_t v; + const uint8_t *bp = (const uint8_t *)p; - memcpy(&v, p, sizeof(v)); - return fdt64_to_cpu(v); + return ((uint64_t)bp[0] << 56) + | ((uint64_t)bp[1] << 48) + | ((uint64_t)bp[2] << 40) + | ((uint64_t)bp[3] << 32) + | ((uint64_t)bp[4] << 24) + | ((uint64_t)bp[5] << 16) + | ((uint64_t)bp[6] << 8) + | bp[7]; } /**********************************************************************/