[PATCH 2/2] x86, boot: Use regparm=0 for memcpy and memset when using clang

Michael Davidson
2017-03-15T21:49:05Z

Use the standard regparm=0 calling convention for memcpy and
memset when building with clang.

This is a work around for a long standing clang bug
(see https://llvm.org/bugs/show_bug.cgi?id=3997) where
clang always uses the standard regparm=0 calling convention
for any implcit calls to memcpy and memset that it generates
(eg for structure assignments and initialization) even if an
alternate calling convention such as regparm=3 has been specified.

Signed-off-by: Michael Davidson <md@google.com>
---
arch/x86/boot/copy.S | 15 +++++++++++++--
arch/x86/boot/string.h | 13 +++++++++++++
2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/copy.S b/arch/x86/boot/copy.S
index 1eb7d298b47d..57142d1ad0d2 100644
--- a/arch/x86/boot/copy.S
+++ b/arch/x86/boot/copy.S
@@ -18,6 +18,12 @@
.text

GLOBAL(memcpy)
+#ifdef __clang__ /* Use normal ABI calling conventions */
+ movw 4(%esp), %ax
+ movw 8(%esp), %dx
+ movw 12(%esp), %cx
+#endif
+_memcpy:
pushw %si
pushw %di
movw %ax, %di
@@ -34,6 +40,11 @@ GLOBAL(memcpy)
ENDPROC(memcpy)

GLOBAL(memset)
+#ifdef __clang__ /* Use normal ABI calling conventions */
+ movw 4(%esp), %ax
+ movw 8(%esp), %dx
+ movw 12(%esp), %cx
+#endif
pushw %di
movw %ax, %di
movzbl %dl, %eax
@@ -52,7 +63,7 @@ GLOBAL(copy_from_fs)
pushw %ds
pushw %fs
popw %ds
- calll memcpy
+ calll _memcpy
popw %ds
retl
ENDPROC(copy_from_fs)
@@ -61,7 +72,7 @@ GLOBAL(copy_to_fs)
pushw %es
pushw %fs
popw %es
- calll memcpy
+ calll _memcpy
popw %es
retl
ENDPROC(copy_to_fs)
diff --git a/arch/x86/boot/string.h b/arch/x86/boot/string.h
index 113588ddb43f..e735cccb3fc8 100644
--- a/arch/x86/boot/string.h
+++ b/arch/x86/boot/string.h
@@ -6,8 +6,21 @@
#undef memset
#undef memcmp

+/*
+ * Use normal ABI calling conventions - i.e. regparm(0) -
+ * for memcpy() and memset() if we are building the real
+ * mode setup code with clang since clang may make implicit
+ * calls to these functions that assume regparm(0).
+ */
+#if defined(_SETUP) && defined(__clang__)
+void __attribute__((regparm(0))) *memcpy(void *dst, const void *src,
+ size_t len);
+void __attribute__((regparm(0))) *memset(void *dst, int c, size_t len);
+#else
void *memcpy(void *dst, const void *src, size_t len);
void *memset(void *dst, int c, size_t len);
+#endif
+
int memcmp(const void *s1, const void *s2, size_t len);

/*
--
2.12.0.367.g23dc2f6d3c-goog