[coreboot-gerrit] Change in ...coreboot[master]: arch/x86/mmio: Avoid pointer aliasing in write8()

[Nico Huber (Code Review)]

Nico Huber has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/31945

Change subject: arch/x86/mmio: Avoid pointer aliasing in write8()
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arch/x86/mmio: Avoid pointer aliasing in write8()

Don't literally dereference a pointer to `char`. Use array
indexing instead to avoid aliasing rules. Otherwise, the
compiler might treat any memory as clobbered.

Change-Id: I441c27e789ad92a8125c92837244474a26250c8a
Signed-off-by: Nico Huber 
---
M src/arch/x86/include/arch/mmio.h
1 file changed, 9 insertions(+), 1 deletion(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/45/31945/1

diff --git a/src/arch/x86/include/arch/mmio.h b/src/arch/x86/include/arch/mmio.h
index f271a97..790b699 100644
--- a/src/arch/x86/include/arch/mmio.h
+++ b/src/arch/x86/include/arch/mmio.h
@@ -45,7 +45,15 @@
 static __always_inline void write8(volatile void *addr,
    uint8_t value)
 {
-	*((volatile uint8_t *)(addr)) = value;
+	/*
+	 * Don't literally dereference a pointer to `char`. Use array
+	 * indexing instead to avoid aliasing rules. Otherwise, the
+	 * compiler might treat any memory as clobbered.
+	 */
+	volatile struct {
+		uint8_t reg[1];
+	} *const ref = addr;
+	ref->reg[0] = value;
 }

static __always_inline void write16(volatile void *addr,