[coreboot-gerrit] New patch to review for coreboot: Avoid crashing on access to 0

[Patrick Georgi (pgeorgi@google.com)]

Patrick Georgi (pgeorgi at google.com) just uploaded a new patch set to gerrit, which you can find at http://review.coreboot.org/12294

-gerrit

commit 23d76695537027249bd4458a86a50b3bdfa1cfe6
Author: Patrick Georgi <patrick at georgi-clan.de>
Date:   Fri Oct 30 15:40:20 2015 +0100

    Avoid crashing on access to 0
    
    Some compilers add a crash (eg. ud2 on x86) when predictably accessing 0
    (because it's undefined behaviour), so do the actual accesses in
    assembler to shut up the language lawyerly compiler.
    
    Change-Id: I6aa6f28283281ebae73d6349811e290bf1b99483
    Signed-off-by: Patrick Georgi <patrick at georgi-clan.de>
---
 src/arch/x86/include/arch/io.h | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/src/arch/x86/include/arch/io.h b/src/arch/x86/include/arch/io.h
index 5c85019..01533d5 100644
--- a/src/arch/x86/include/arch/io.h
+++ b/src/arch/x86/include/arch/io.h
@@ -145,32 +145,38 @@ static inline void insl(uint16_t port, void *addr, unsigned long count)
 
 static inline __attribute__((always_inline)) uint8_t read8(const volatile void *addr)
 {
-	return *((volatile uint8_t *)(addr));
+	uint8_t res;
+	asm ("mov (%1), %0" : "=r" (res) : "r" (addr));
+	return res;
 }
 
 static inline __attribute__((always_inline)) uint16_t read16(const volatile void *addr)
 {
-	return *((volatile uint16_t *)(addr));
+	uint16_t res;
+	asm ("mov (%1), %0" : "=r" (res) : "r" (addr));
+	return res;
 }
 
 static inline __attribute__((always_inline)) uint32_t read32(const volatile void *addr)
 {
-	return *((volatile uint32_t *)(addr));
+	uint32_t res;
+	asm ("mov (%1), %0" : "=r" (res) : "r" (addr));
+	return res;
 }
 
 static inline __attribute__((always_inline)) void write8(volatile void *addr, uint8_t value)
 {
-	*((volatile uint8_t *)(addr)) = value;
+	asm ("mov %0, (%1)" :: "r" (value), "r" (addr) : "memory");
 }
 
 static inline __attribute__((always_inline)) void write16(volatile void *addr, uint16_t value)
 {
-	*((volatile uint16_t *)(addr)) = value;
+	asm ("mov %0, (%1)" :: "r" (value), "r" (addr) : "memory");
 }
 
 static inline __attribute__((always_inline)) void write32(volatile void *addr, uint32_t value)
 {
-	*((volatile uint32_t *)(addr)) = value;
+	asm ("mov %0, (%1)" :: "r" (value), "r" (addr) : "memory");
 }
 
 /* Conflicts with definition in lib.h */