RISC-V: Stop relying on GCC's register allocator's hueristics

GCC allows users to hint to the register allocation that a variable should be
placed in a register by using a syntax along the lines of

    function(...) {
        register long in_REG __asm__("REG");
    }

We've abused this a bit throughout the RISC-V port to access fixed registers
directly as C variables.  In practice it's never going to blow up because GCC
isn't going to allocate these registers, but it's not a well defined syntax so
we really shouldn't be relying upon this.  Luckily there is a very similar but
well defined syntax that allows us to still access these registers directly as
C variables, which is to simply declare the register variables globally.  For
fixed variables this doesn't change the ABI.

LLVM disallows this ambiguous syntax, so this isn't just strictly a formatting
change.

Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/arch/riscv/include/asm/current.h b/arch/riscv/include/asm/current.h
index dd973efe5d7c..1de233d8e8de 100644
--- a/arch/riscv/include/asm/current.h
+++ b/arch/riscv/include/asm/current.h
@@ -17,6 +17,8 @@
 
 struct task_struct;
 
+register struct task_struct *riscv_current_is_tp __asm__("tp");
+
 /*
  * This only works because "struct thread_info" is at offset 0 from "struct
  * task_struct".  This constraint seems to be necessary on other architectures
@@ -26,8 +28,7 @@ struct task_struct;
  */
 static __always_inline struct task_struct *get_current(void)
 {
-	register struct task_struct *tp __asm__("tp");
-	return tp;
+	return riscv_current_is_tp;
 }
 
 #define current get_current()