[PATCH v2] msvcrt: Avoid disallowed unaligned writes in memset on ARM

[Martin Storsjö]

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(a)martin.st>
---
v2: Using a macro to hide the difference.
---
 dlls/msvcrt/string.c | 32 ++++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/dlls/msvcrt/string.c b/dlls/msvcrt/string.c
index f2b1b4a5b11..6fade4d80fc 100644
--- a/dlls/msvcrt/string.c
+++ b/dlls/msvcrt/string.c
@@ -2876,17 +2876,28 @@ void *__cdecl memset(void *dst, int c, size_t n)
     unsigned char *d = (unsigned char *)dst;
     size_t a = 0x20 - ((uintptr_t)d & 0x1f);
 
+#ifdef __arm__
+#define MEMSET_UNALIGNED_64(dst, off, val) do {                               \
+        *(volatile uint32_t *)((dst) + (off) + 0) = val;                      \
+        *(volatile uint32_t *)((dst) + (off) + 4) = val;                      \
+    } while (0)
+#else
+#define MEMSET_UNALIGNED_64(dst, off, val) do {                               \
+        *(uint64_t *)((dst) + (off)) = val;                                   \
+    } while (0)
+#endif
+
     if (n >= 16)
     {
-        *(uint64_t *)(d + 0) = v;
-        *(uint64_t *)(d + 8) = v;
-        *(uint64_t *)(d + n - 16) = v;
-        *(uint64_t *)(d + n - 8) = v;
+        MEMSET_UNALIGNED_64(d, 0, v);
+        MEMSET_UNALIGNED_64(d, 8, v);
+        MEMSET_UNALIGNED_64(d, n - 16, v);
+        MEMSET_UNALIGNED_64(d, n - 8, v);
         if (n <= 32) return dst;
-        *(uint64_t *)(d + 16) = v;
-        *(uint64_t *)(d + 24) = v;
-        *(uint64_t *)(d + n - 32) = v;
-        *(uint64_t *)(d + n - 24) = v;
+        MEMSET_UNALIGNED_64(d, 16, v);
+        MEMSET_UNALIGNED_64(d, 24, v);
+        MEMSET_UNALIGNED_64(d, n - 32, v);
+        MEMSET_UNALIGNED_64(d, n - 24, v);
         if (n <= 64) return dst;
 
         n = (n - a) & ~0x1f;
@@ -2895,8 +2906,8 @@ void *__cdecl memset(void *dst, int c, size_t n)
     }
     if (n >= 8)
     {
-        *(uint64_t *)d = v;
-        *(uint64_t *)(d + n - 8) = v;
+        MEMSET_UNALIGNED_64(d, 0, v);
+        MEMSET_UNALIGNED_64(d, n - 8, v);
         return dst;
     }
     if (n >= 4)
@@ -2916,6 +2927,7 @@ void *__cdecl memset(void *dst, int c, size_t n)
         *(uint8_t *)d = v;
         return dst;
     }
+#undef MEMSET_UNALIGNED_64
     return dst;
 }
 
-- 
2.25.1