[PATCH 5.4 07/76] mips: lib: uncached: fix non-standard usage of variable sp

From: Greg Kroah-Hartman
Date: Mon Jan 18 2021 - 14:17:54 EST

From: Anders Roxell <anders.roxell@xxxxxxxxxx>

commit 5b058973d3205578aa6c9a71392e072a11ca44ef upstream.

When building mips tinyconfig with clang the following warning show up:

arch/mips/lib/uncached.c:45:6: warning: variable 'sp' is uninitialized when used here [-Wuninitialized]
if (sp >= (long)CKSEG0 && sp < (long)CKSEG2)
arch/mips/lib/uncached.c:40:18: note: initialize the variable 'sp' to silence this warning
register long sp __asm__("$sp");
= 0
1 warning generated.

Rework to make an explicit inline move, instead of the non-standard use
of specifying registers for local variables. This is what's written
from the gcc-10 manual [1] about specifying registers for local

" Specifying Registers for Local Variables

"The only supported use for this feature is to specify registers for
input and output operands when calling Extended 'asm' (*note Extended
Asm::). [...]".

[1] https://docs.w3cub.com/gcc~10/local-register-variables
Signed-off-by: Anders Roxell <anders.roxell@xxxxxxxxxx>
Reported-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/mips/lib/uncached.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/mips/lib/uncached.c
+++ b/arch/mips/lib/uncached.c
@@ -37,10 +37,12 @@
unsigned long run_uncached(void *func)
- register long sp __asm__("$sp");
register long ret __asm__("$2");
long lfunc = (long)func, ufunc;
long usp;
+ long sp;
+ __asm__("move %0, $sp" : "=r" (sp));

if (sp >= (long)CKSEG0 && sp < (long)CKSEG2)
usp = CKSEG1ADDR(sp);