linux-kernel - [PATCH] [v2] x86: math-emu: Fix function cast warning

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Date:   Mon, 22 Mar 2021 22:48:19 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Bill Metzenthen <billm@...bpc.org.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org
Cc:     Arnd Bergmann <arnd@...db.de>, "H. Peter Anvin" <hpa@...or.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] [v2] x86: math-emu: Fix function cast warning

From: Arnd Bergmann <arnd@...db.de>

Building with 'make W=1', gcc points out that casting between
incompatible function types can be dangerous:

arch/x86/math-emu/fpu_trig.c:1638:60: error: cast between incompatible function types from ‘int (*)(FPU_REG *, u_char)’ {aka ‘int (*)(struct fpu__reg *, unsigned char)’} to ‘void (*)(FPU_REG *, u_char)’ {aka ‘void (*)(struct fpu__reg *, unsigned char)’} [-Werror=cast-function-type]
 1638 |         fprem, fyl2xp1, fsqrt_, fsincos, frndint_, fscale, (FUNC_ST0) fsin, fcos
      |                                                            ^

This one seems harmless, but it is easy enough to work around it by
adding an intermediate function that adjusts the return type.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
v2: use consistent naming for the function types, as
    pointed out by Ingo Molnar
---
 arch/x86/math-emu/fpu_trig.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/math-emu/fpu_trig.c b/arch/x86/math-emu/fpu_trig.c
index 4a9887851ad8..990d847ae902 100644
--- a/arch/x86/math-emu/fpu_trig.c
+++ b/arch/x86/math-emu/fpu_trig.c
@@ -547,7 +547,7 @@ static void frndint_(FPU_REG *st0_ptr, u_char st0_tag)
 		single_arg_error(st0_ptr, st0_tag);
 }
 
-static int fsin(FPU_REG *st0_ptr, u_char tag)
+static int f_sin(FPU_REG *st0_ptr, u_char tag)
 {
 	u_char arg_sign = getsign(st0_ptr);
 
@@ -608,6 +608,11 @@ static int fsin(FPU_REG *st0_ptr, u_char tag)
 	}
 }
 
+static void fsin(FPU_REG *st0_ptr, u_char tag)
+{
+	f_sin(st0_ptr, tag);
+}
+
 static int f_cos(FPU_REG *st0_ptr, u_char tag)
 {
 	u_char st0_sign;
@@ -724,7 +729,7 @@ static void fsincos(FPU_REG *st0_ptr, u_char st0_tag)
 	}
 
 	reg_copy(st0_ptr, &arg);
-	if (!fsin(st0_ptr, st0_tag)) {
+	if (!f_sin(st0_ptr, st0_tag)) {
 		push();
 		FPU_copy_to_reg0(&arg, st0_tag);
 		f_cos(&st(0), st0_tag);
@@ -1635,7 +1640,7 @@ void FPU_triga(void)
 }
 
 static FUNC_ST0 const trig_table_b[] = {
-	fprem, fyl2xp1, fsqrt_, fsincos, frndint_, fscale, (FUNC_ST0) fsin, fcos
+	fprem, fyl2xp1, fsqrt_, fsincos, frndint_, fscale, fsin, fcos
 };
 
 void FPU_trigb(void)
-- 
2.29.2