[PATCH 4/4] x86, boot: Work around clang PR18415.

[David Woodhouse <David.Woodhouse@intel.com>]

Clang's intrinsics ignore -mregparm=3 when they fall back to calling the
out-of-line implementations. Putting the args on the stack when memcpy()
expects them in registers is not a recipe for a happy kernel.

This bites with -m32 too, so clang is presumably catastrophically
broken for the i386 kernel until this is fixed, unless I'm missing
something.

For information/testing only; do not apply. With this, I can use
'clang -m16' to build all the kernel's 16-bit code and get a successful
boot.

Not-signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
---
 arch/x86/boot/boot.h   | 2 ++
 arch/x86/boot/memory.c | 7 ++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index ef72bae..1182dc9 100644
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h
@@ -232,8 +232,10 @@ void *copy_from_gs(void *dst, addr_t src, size_t len);
 void *memcpy(void *dst, void *src, size_t len);
 void *memset(void *dst, int c, size_t len);
 
+#ifndef __clang__ /* PR18415 */
 #define memcpy(d,s,l) __builtin_memcpy(d,s,l)
 #define memset(d,c,l) __builtin_memset(d,c,l)
+#endif
 
 /* a20.c */
 int enable_a20(void);
diff --git a/arch/x86/boot/memory.c b/arch/x86/boot/memory.c
index db75d07..7af6504 100644
--- a/arch/x86/boot/memory.c
+++ b/arch/x86/boot/memory.c
@@ -63,8 +63,13 @@ static int detect_memory_e820(void)
 			count = 0;
 			break;
 		}
-
+#ifdef __clang__
+		/* PR18415 */
+		memcpy(desc, &buf, sizeof(*desc));
+		desc++;
+#else
 		*desc++ = buf;
+#endif
 		count++;
 	} while (ireg.ebx && count < ARRAY_SIZE(boot_params.e820_map));
 
-- 
1.8.4.2