[Xen-devel] [PATCH 1/4] x86: enhance rsp-relative calculations

["Jan Beulich" <JBeulich@xxxxxxxx>]

The use of "or" in GET_CPUINFO_FIELD so far wasn't ideal, as it doesn't
lend itself to folding this operation with a possibly subsequent one
(e.g. the well known mov+add=lea conversion). Split out the sub-
operations, and shorten assembly code slightly with this.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -445,10 +445,10 @@ domain_crash_synchronous_string:
 
 ENTRY(domain_crash_synchronous)
         # Get out of the guest-save area of the stack.
-        GET_CPUINFO_FIELD(CPUINFO_guest_cpu_user_regs,%rax)
-        movq  %rax,%rsp
+        GET_STACK_BASE(%rax)
+        leaq  STACK_CPUINFO_FIELD(guest_cpu_user_regs)(%rax),%rsp
         # create_bounce_frame() temporarily clobbers CS.RPL. Fix up.
-        GET_CURRENT(%rax)
+        __GET_CURRENT(%rax)
         movq  VCPU_domain(%rax),%rax
         testb $1,DOMAIN_is_32bit_pv(%rax)
         setz  %al
@@ -622,7 +622,7 @@ handle_ist_exception:
         testb $3,UREGS_cs(%rsp)
         jz    1f
         /* Interrupted guest context. Copy the context to stack bottom. */
-        GET_CPUINFO_FIELD(CPUINFO_guest_cpu_user_regs,%rdi)
+        GET_CPUINFO_FIELD(guest_cpu_user_regs,%rdi)
         movq  %rsp,%rsi
         movl  $UREGS_kernel_sizeof/8,%ecx
         movq  %rdi,%rsp
--- a/xen/include/asm-x86/asm_defns.h
+++ b/xen/include/asm-x86/asm_defns.h
@@ -44,6 +44,21 @@ void ret_from_intr(void);
         .subsection 0;            \
         .Llikely.tag:
 
+#define STACK_CPUINFO_FIELD(field) (STACK_SIZE-CPUINFO_sizeof+CPUINFO_##field)
+#define GET_STACK_BASE(reg)                       \
+        movq $~(STACK_SIZE-1),reg;                \
+        andq %rsp,reg
+
+#define GET_CPUINFO_FIELD(field, reg)             \
+        GET_STACK_BASE(reg);                      \
+        addq $STACK_CPUINFO_FIELD(field),reg
+
+#define __GET_CURRENT(reg)                        \
+        movq STACK_CPUINFO_FIELD(current_vcpu)(reg),reg
+#define GET_CURRENT(reg)                          \
+        GET_STACK_BASE(reg);                      \
+        __GET_CURRENT(reg)
+
 #endif
 
 #endif /* __X86_ASM_DEFNS_H__ */
--- a/xen/include/asm-x86/x86_64/asm_defns.h
+++ b/xen/include/asm-x86/x86_64/asm_defns.h
@@ -111,14 +111,6 @@ STR(IRQ) #nr "_interrupt:\n\t"          
     "movl $"#nr",4(%rsp)\n\t"                   \
     "jmp common_interrupt");
 
-#define GET_CPUINFO_FIELD(field,reg)                    \
-        movq $~(STACK_SIZE-1),reg;                      \
-        andq %rsp,reg;                                  \
-        orq  $(STACK_SIZE-CPUINFO_sizeof+field),reg;
-#define GET_CURRENT(reg)                                \
-        GET_CPUINFO_FIELD(CPUINFO_current_vcpu,reg)     \
-        movq (reg),reg;
-
 #ifdef __ASSEMBLY__
 # define _ASM_EX(p) p-.
 #else




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