[Devel] [PATCH RHEL7 COMMIT] x86/asm: Use register variable to get stack pointer value

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-1127.8.2.vz7.161.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1127.8.2.vz7.161.1
------>
commit 2261ff8ef6beb0da20712141bfb2e61588dad5ce
Author: Andrey Ryabinin <aryabinin at virtuozzo.com>
Date:   Mon May 25 17:55:54 2020 +0300

    x86/asm: Use register variable to get stack pointer value
    
    ms commit 196bd485ee4f (part)
    
    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, %<dst>" instructions:
    
      -mov    %rsp,%rdx
      -sub    %rdx,%rax
      -cmp    $0x3fff,%rax
      -ja     ffffffff810722fd <ist_begin_non_atomic+0x2d>
    
      +sub    %rsp,%rax
      +cmp    $0x3fff,%rax
      +ja     ffffffff810722fa <ist_begin_non_atomic+0x2a>
    
    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 <aryabinin at virtuozzo.com>
    
    Reviewed-by: Josh Poimboeuf <jpoimboe at redhat.com>
    Cc: Andy Lutomirski <luto at kernel.org>
    Cc: Linus Torvalds <torvalds at linux-foundation.org>
    Cc: Peter Zijlstra <peterz at infradead.org>
    Cc: Thomas Gleixner <tglx at linutronix.de>
    Link: http://lkml.kernel.org/r/20170929141537.29167-1-aryabinin@virtuozzo.com
    Signed-off-by: Ingo Molnar <mingo at kernel.org>
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    
    =====================
    Patchset description:
    
    This ports support for down_read_killable(),
    which is a prerequisite for pernet_ops_rwsem.
    
    https://jira.sw.ru/browse/PSBM-104158
---
 arch/x86/include/asm/asm.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 41efcf1746338..b15820cf90d20 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -83,4 +83,9 @@
 	" .popsection\n"
 #endif
 
+#ifndef __ASSEMBLY__
+register unsigned long current_stack_pointer asm(_ASM_SP);
+#define ASM_CALL_CONSTRAINT "+r" (current_stack_pointer)
+#endif
+
 #endif /* _ASM_X86_ASM_H */