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* [PATCH] x86: math-emu: hide clang warnings for 16-bit overflow
@ 2019-07-12  9:08 Arnd Bergmann
  2019-07-16 21:22 ` [tip:x86/urgent] x86: math-emu: Hide " tip-bot for Arnd Bergmann
  2019-07-16 22:46 ` tip-bot for Arnd Bergmann
  0 siblings, 2 replies; 3+ messages in thread
From: Arnd Bergmann @ 2019-07-12  9:08 UTC (permalink / raw)
  To: Bill Metzenthen, Thomas Gleixner, Ingo Molnar, Borislav Petkov, x86
  Cc: Arnd Bergmann, H. Peter Anvin, linux-kernel, clang-built-linux

clang warns about a few parts of the math-emu implementation
where a 16-bit integer becomes negative during assignment:

arch/x86/math-emu/poly_tan.c:88:35: error: implicit conversion from 'int' to 'short' changes value from 49216 to -16320 [-Werror,-Wconstant-conversion]
                                      (0x41 + EXTENDED_Ebias) | SIGN_Negative);
                                      ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~
arch/x86/math-emu/fpu_emu.h:180:58: note: expanded from macro 'setexponent16'
 #define setexponent16(x,y)  { (*(short *)&((x)->exp)) = (y); }
                                                      ~  ^
arch/x86/math-emu/reg_constant.c:37:32: error: implicit conversion from 'int' to 'short' changes value from 49085 to -16451 [-Werror,-Wconstant-conversion]
FPU_REG const CONST_PI2extra = MAKE_REG(NEG, -66,
                               ^~~~~~~~~~~~~~~~~~
arch/x86/math-emu/reg_constant.c:21:25: note: expanded from macro 'MAKE_REG'
                ((EXTENDED_Ebias+(e)) | ((SIGN_##s != 0)*0x8000)) }
                 ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
arch/x86/math-emu/reg_constant.c:48:28: error: implicit conversion from 'int' to 'short' changes value from 65535 to -1 [-Werror,-Wconstant-conversion]
FPU_REG const CONST_QNaN = MAKE_REG(NEG, EXP_OVER, 0x00000000, 0xC0000000);
                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/x86/math-emu/reg_constant.c:21:25: note: expanded from macro 'MAKE_REG'
                ((EXTENDED_Ebias+(e)) | ((SIGN_##s != 0)*0x8000)) }
                 ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~

The code seems correct to me, so add a typecast to shut up the warnings.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/x86/math-emu/fpu_emu.h      | 2 +-
 arch/x86/math-emu/reg_constant.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/math-emu/fpu_emu.h b/arch/x86/math-emu/fpu_emu.h
index a5a41ec58072..0c122226ca56 100644
--- a/arch/x86/math-emu/fpu_emu.h
+++ b/arch/x86/math-emu/fpu_emu.h
@@ -177,7 +177,7 @@ static inline void reg_copy(FPU_REG const *x, FPU_REG *y)
 #define setexponentpos(x,y) { (*(short *)&((x)->exp)) = \
   ((y) + EXTENDED_Ebias) & 0x7fff; }
 #define exponent16(x)         (*(short *)&((x)->exp))
-#define setexponent16(x,y)  { (*(short *)&((x)->exp)) = (y); }
+#define setexponent16(x,y)  { (*(short *)&((x)->exp)) = (u16)(y); }
 #define addexponent(x,y)    { (*(short *)&((x)->exp)) += (y); }
 #define stdexp(x)           { (*(short *)&((x)->exp)) += EXTENDED_Ebias; }
 
diff --git a/arch/x86/math-emu/reg_constant.c b/arch/x86/math-emu/reg_constant.c
index 8dc9095bab22..742619e94bdf 100644
--- a/arch/x86/math-emu/reg_constant.c
+++ b/arch/x86/math-emu/reg_constant.c
@@ -18,7 +18,7 @@
 #include "control_w.h"
 
 #define MAKE_REG(s, e, l, h) { l, h, \
-		((EXTENDED_Ebias+(e)) | ((SIGN_##s != 0)*0x8000)) }
+		(u16)((EXTENDED_Ebias+(e)) | ((SIGN_##s != 0)*0x8000)) }
 
 FPU_REG const CONST_1 = MAKE_REG(POS, 0, 0x00000000, 0x80000000);
 #if 0
-- 
2.20.0


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2019-07-12  9:08 [PATCH] x86: math-emu: hide clang warnings for 16-bit overflow Arnd Bergmann
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