Fixing volatile and memory attributes for assembly.

For volatile:
You can prevent an asm instruction from being deleted by writing the
keyword volatile after the asm. [...] The volatile keyword indicates
that the instruction has important side-effects. GCC will not
delete a volatile asm if it is reachable.
and
An asm instruction without any output operands will be treated
identically to a volatile asm instruction.

And for memory:
This will cause GCC to not keep memory values cached in
registers across the assembler instruction and not optimize
stores or loads to that memory.

See also:
https://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/Extended-Asm.html
http://stackoverflow.com/questions/14449141/the-difference-between-asm-asm-volatile-and-clobbering-memory

1 files changed, 9 insertions, 8 deletions

diff --git a/src/controlregs.rs b/src/controlregs.rs
index 89242c2..b6cd334 100644
--- a/src/controlregs.rs
+++ b/src/controlregs.rs
@@ -1,44 +1,45 @@
-/// Contains various flags to control operations.
+//! Functions to read and write control registers.
+
 pub unsafe fn cr0() -> u64
 {
     let ret: u64;
-    asm!("mov %cr0, $0" : "=r" (ret) : );
+    asm!("mov %cr0, $0" : "=r" (ret));
     ret
 }
 
 /// Write cr0.
 pub unsafe fn cr0_write(val: u64)
 {
-    asm!("mov $0, %cr0" :: "r" (val));
+    asm!("mov $0, %cr0" :: "r" (val) : "memory");
 }
 
 /// Contains page-fault linear address.
 pub unsafe fn cr2() -> u64 {
     let ret: u64;
-    asm!("mov %cr2, $0" : "=r" (ret) :);
+    asm!("mov %cr2, $0" : "=r" (ret));
     ret
 }
 
 /// Contains page-table root pointer.
 pub unsafe fn cr3() -> u64 {
     let ret: u64;
-    asm!("mov %cr3, $0" : "=r" (ret) :);
+    asm!("mov %cr3, $0" : "=r" (ret));
     ret
 }
 
 /// Switch page-table PML4 pointer.
 pub unsafe fn cr3_write(val: u64) {
-    asm!("mov $0, %cr3" :: "r" (val));
+    asm!("mov $0, %cr3" :: "r" (val) : "memory");
 }
 
 /// Contains various flags to control operations in protected mode.
 pub unsafe fn cr4() -> u64 {
     let ret: u64;
-    asm!("mov %cr4, $0" : "=r" (ret) :);
+    asm!("mov %cr4, $0" : "=r" (ret));
     ret
 }
 
 /// Write cr4.
 pub unsafe fn cr4_write(val: u64) {
-    asm!("mov $0, %cr4" :: "r" (val));
+    asm!("mov $0, %cr4" :: "r" (val) : "memory");
 }