arch/x86: (Intel64) move RAX to volatile register set

This used to be part of the "restore always" set of registers because
__swap was expected to return a value.  No longer required, so RAX is
moved to the volatile registers and we save a few cycles occasionally.

Signed-off-by: Charles E. Youse <[email protected]>

Author: Charles E. Youse

arch/x86/core/intel64/locore.S

@@ -222,12 +222,12 @@ __resume:
 	movq _thread_offset_to_r13(%rdi), %r13
 	movq _thread_offset_to_r14(%rdi), %r14
 	movq _thread_offset_to_r15(%rdi), %r15
-	movq _thread_offset_to_rax(%rdi), %rax
 
 	testb $X86_THREAD_FLAG_ALL, _thread_offset_to_flags(%rdi)
 	jz 1f
 
 	fxrstor _thread_offset_to_sse(%rdi)
+	movq _thread_offset_to_rax(%rdi), %rax
 	movq _thread_offset_to_rcx(%rdi), %rcx
 	movq _thread_offset_to_rdx(%rdi), %rdx
 	movq _thread_offset_to_rsi(%rdi), %rsi

arch/x86/core/offsets/intel64_offsets.c

@@ -16,8 +16,8 @@ GEN_OFFSET_SYM(_callee_saved_t, r14);
 GEN_OFFSET_SYM(_callee_saved_t, r15);
 GEN_OFFSET_SYM(_callee_saved_t, rip);
 GEN_OFFSET_SYM(_callee_saved_t, rflags);
-GEN_OFFSET_SYM(_callee_saved_t, rax);
 
+GEN_OFFSET_SYM(_thread_arch_t, rax);
 GEN_OFFSET_SYM(_thread_arch_t, rcx);
 GEN_OFFSET_SYM(_thread_arch_t, rdx);
 GEN_OFFSET_SYM(_thread_arch_t, rsi);

arch/x86/include/intel64/kernel_arch_thread.h

@@ -30,14 +30,14 @@ struct _callee_saved {
 	u64_t r15;
 	u64_t rip;
 	u64_t rflags;
-	u64_t rax;
 };
 
 typedef struct _callee_saved _callee_saved_t;
 
 struct _thread_arch {
 	u8_t flags;
 
+	u64_t rax;
 	u64_t rcx;
 	u64_t rdx;
 	u64_t rsi;

arch/x86/include/intel64/offsets_short_arch.h

@@ -36,7 +36,7 @@
 	(___thread_t_callee_saved_OFFSET + ___callee_saved_t_rflags_OFFSET)
 
 #define _thread_offset_to_rax \
-	(___thread_t_callee_saved_OFFSET + ___callee_saved_t_rax_OFFSET)
+	(___thread_t_arch_OFFSET + ___thread_arch_t_rax_OFFSET)
 
 #define _thread_offset_to_rcx \
 	(___thread_t_arch_OFFSET + ___thread_arch_t_rcx_OFFSET)