[PATCH] msvcrt: Avoid disallowed unaligned writes in memset on ARM

[Martin Storsjo]

From: Martin Storsjö <martin at martin.st>

This fixes a regression in memset on ARM since
7b17d7081512db52ef852705445762ac4016c29f.

ARM can do 64 bit writes with the STRD instruction, but that
instruction requires a 32 bit aligned address - while these stores
are unaligned.

Two consecutive stores to uint32_t* pointers can also be fused
into one single STRD, as a uint32_t* is supposed to be properly
aligned - therefore, do these stores as stores to volatile uint32_t*
to avoid fusing them.

Signed-off-by: Martin Storsjö <martin at martin.st>
---
 dlls/msvcrt/string.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/dlls/msvcrt/string.c b/dlls/msvcrt/string.c
index f2b1b4a5b11..bf491a91f40 100644
--- a/dlls/msvcrt/string.c
+++ b/dlls/msvcrt/string.c
@@ -2878,15 +2878,37 @@ void *__cdecl memset(void *dst, int c, size_t n)
 
     if (n >= 16)
     {
+#ifdef __arm__
+        *(volatile uint32_t *)(d + 0) = v;
+        *(volatile uint32_t *)(d + 4) = v;
+        *(volatile uint32_t *)(d + 8) = v;
+        *(volatile uint32_t *)(d + 12) = v;
+        *(volatile uint32_t *)(d + n - 16) = v;
+        *(volatile uint32_t *)(d + n - 12) = v;
+        *(volatile uint32_t *)(d + n - 8) = v;
+        *(volatile uint32_t *)(d + n - 4) = v;
+#else
         *(uint64_t *)(d + 0) = v;
         *(uint64_t *)(d + 8) = v;
         *(uint64_t *)(d + n - 16) = v;
         *(uint64_t *)(d + n - 8) = v;
+#endif
         if (n <= 32) return dst;
+#ifdef __arm__
+        *(volatile uint32_t *)(d + 16) = v;
+        *(volatile uint32_t *)(d + 20) = v;
+        *(volatile uint32_t *)(d + 24) = v;
+        *(volatile uint32_t *)(d + 28) = v;
+        *(volatile uint32_t *)(d + n - 32) = v;
+        *(volatile uint32_t *)(d + n - 28) = v;
+        *(volatile uint32_t *)(d + n - 24) = v;
+        *(volatile uint32_t *)(d + n - 20) = v;
+#else
         *(uint64_t *)(d + 16) = v;
         *(uint64_t *)(d + 24) = v;
         *(uint64_t *)(d + n - 32) = v;
         *(uint64_t *)(d + n - 24) = v;
+#endif
         if (n <= 64) return dst;
 
         n = (n - a) & ~0x1f;
@@ -2895,8 +2917,15 @@ void *__cdecl memset(void *dst, int c, size_t n)
     }
     if (n >= 8)
     {
+#ifdef __arm__
+        *(volatile uint32_t *)d = v;
+        *(volatile uint32_t *)(d + 4) = v;
+        *(volatile uint32_t *)(d + n - 4) = v;
+        *(volatile uint32_t *)(d + n - 8) = v;
+#else
         *(uint64_t *)d = v;
         *(uint64_t *)(d + n - 8) = v;
+#endif
         return dst;
     }
     if (n >= 4)
-- 
2.25.1