[PATCH 3.2 057/104] x86/asm: Use register variable to get stack pointer value

[Ben Hutchings]

3.2.101-rc1 review patch.  If anyone has any objections, please let me know.

--

From: Andrey Ryabinin 

commit 196bd485ee4f03ce4c690bfcf38138abfcd0a4bc upstream.

Currently we use current_stack_pointer() function to get the value
of the stack pointer register. Since commit:

  f5caf621ee35 ("x86/asm: Fix inline asm call constraints for Clang")

... we have a stack register variable declared. It can be used instead of
current_stack_pointer() function which allows to optimize away some
excessive "mov %rsp, %" instructions:

 -mov%rsp,%rdx
 -sub%rdx,%rax
 -cmp$0x3fff,%rax
 -ja 810722fd 

 +sub%rsp,%rax
 +cmp$0x3fff,%rax
 +ja 810722fa 

Remove current_stack_pointer(), rename __asm_call_sp to current_stack_pointer
and use it instead of the removed function.

Signed-off-by: Andrey Ryabinin 
Reviewed-by: Josh Poimboeuf 
Cc: Andy Lutomirski 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/20170929141537.29167-1-aryabi...@virtuozzo.com
Signed-off-by: Ingo Molnar 
[dwmw2: We want ASM_CALL_CONSTRAINT for retpoline]
Signed-off-by: David Woodhouse 
Signed-off-by: Razvan Ghitulete 
Signed-off-by: Greg Kroah-Hartman 
[bwh: Backported to 3.2: current_stack_pointer was never changed to a function,
 but was only defined for x86_32]
Signed-off-by: Ben Hutchings 
---
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -59,4 +59,15 @@
" .previous\n"
 #endif
 
+#ifndef __ASSEMBLY__
+/*
+ * This output constraint should be used for any inline asm which has a "call"
+ * instruction.  Otherwise the asm may be inserted before the frame pointer
+ * gets set up by the containing function.  If you forget to do this, objtool
+ * may print a "call without frame pointer save/setup" warning.
+ */
+register unsigned long current_stack_pointer asm(_ASM_SP);
+#define ASM_CALL_CONSTRAINT "+r" (current_stack_pointer)
+#endif
+
 #endif /* _ASM_X86_ASM_H */
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -181,9 +181,6 @@ struct thread_info {
 #ifndef __ASSEMBLY__
 
 
-/* how to get the current stack pointer from C */
-register unsigned long current_stack_pointer asm("esp") __used;
-
 /* how to get the thread information struct from C */
 static inline struct thread_info *current_thread_info(void)
 {

[PATCH 3.2 057/104] x86/asm: Use register variable to get stack pointer value

[Ben Hutchings]

3.2.101-rc1 review patch.  If anyone has any objections, please let me know.

--

From: Andrey Ryabinin 

commit 196bd485ee4f03ce4c690bfcf38138abfcd0a4bc upstream.

Currently we use current_stack_pointer() function to get the value
of the stack pointer register. Since commit:

  f5caf621ee35 ("x86/asm: Fix inline asm call constraints for Clang")

... we have a stack register variable declared. It can be used instead of
current_stack_pointer() function which allows to optimize away some
excessive "mov %rsp, %" instructions:

 -mov%rsp,%rdx
 -sub%rdx,%rax
 -cmp$0x3fff,%rax
 -ja 810722fd 

 +sub%rsp,%rax
 +cmp$0x3fff,%rax
 +ja 810722fa 

Remove current_stack_pointer(), rename __asm_call_sp to current_stack_pointer
and use it instead of the removed function.

Signed-off-by: Andrey Ryabinin 
Reviewed-by: Josh Poimboeuf 
Cc: Andy Lutomirski 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/20170929141537.29167-1-aryabi...@virtuozzo.com
Signed-off-by: Ingo Molnar 
[dwmw2: We want ASM_CALL_CONSTRAINT for retpoline]
Signed-off-by: David Woodhouse 
Signed-off-by: Razvan Ghitulete 
Signed-off-by: Greg Kroah-Hartman 
[bwh: Backported to 3.2: current_stack_pointer was never changed to a function,
 but was only defined for x86_32]
Signed-off-by: Ben Hutchings 
---
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -59,4 +59,15 @@
" .previous\n"
 #endif
 
+#ifndef __ASSEMBLY__
+/*
+ * This output constraint should be used for any inline asm which has a "call"
+ * instruction.  Otherwise the asm may be inserted before the frame pointer
+ * gets set up by the containing function.  If you forget to do this, objtool
+ * may print a "call without frame pointer save/setup" warning.
+ */
+register unsigned long current_stack_pointer asm(_ASM_SP);
+#define ASM_CALL_CONSTRAINT "+r" (current_stack_pointer)
+#endif
+
 #endif /* _ASM_X86_ASM_H */
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -181,9 +181,6 @@ struct thread_info {
 #ifndef __ASSEMBLY__
 
 
-/* how to get the current stack pointer from C */
-register unsigned long current_stack_pointer asm("esp") __used;
-
 /* how to get the thread information struct from C */
 static inline struct thread_info *current_thread_info(void)
 {