[PATCH] x86: math-emu: fix function cast warnings

[Arnd Bergmann]

From: Arnd Bergmann <arnd@xxxxxxxx>

clang-16 warns about casting function pointers with incompatible
prototypes. The x86 math-emu code does this in a number of places
to call some trivial functions that need no arguments:

arch/x86/math-emu/fpu_etc.c:124:14: error: cast from 'void (*)(void)' to 'FUNC_ST0' (aka 'void (*)(struct fpu__reg *, unsigned char)') converts to incompatible function type [-Werror,-Wcast-function-type-strict]
  124 |         fchs, fabs, (FUNC_ST0) FPU_illegal, (FUNC_ST0) FPU_illegal,
      |                     ^~~~~~~~~~~~~~~~~~~~~~
arch/x86/math-emu/fpu_trig.c:1634:19: error: cast from 'void (*)(void)' to 'FUNC_ST0' (aka 'void (*)(struct fpu__reg *, unsigned char)') converts to incompatible function type [-Werror,-Wcast-function-type-strict]
 1634 |         fxtract, fprem1, (FUNC_ST0) fdecstp, (FUNC_ST0) fincstp
      |                          ^~~~~~~~~~~~~~~~~~
arch/x86/math-emu/reg_constant.c:112:53: error: cast from 'void (*)(void)' to 'FUNC_RC' (aka 'void (*)(int)') converts to incompatible function type [-Werror,-Wcast-function-type-strict]
  112 |         fld1, fldl2t, fldl2e, fldpi, fldlg2, fldln2, fldz, (FUNC_RC) FPU_illegal

Change the fdecstp() and fincstp() functions to actually have the correct
prototypes based on the caller, and add wrappers around FPU_illegal()
for adapting those.

Link: https://lore.kernel.org/lkml/20240213095631.454543-1-arnd@xxxxxxxxxx/
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
Resending the version from Feb 13, no changes
---
 arch/x86/math-emu/fpu_etc.c      | 9 +++++++--
 arch/x86/math-emu/fpu_trig.c     | 6 +++---
 arch/x86/math-emu/reg_constant.c | 7 ++++++-
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/arch/x86/math-emu/fpu_etc.c b/arch/x86/math-emu/fpu_etc.c
index 1b118fd93140..39423ec409e1 100644
--- a/arch/x86/math-emu/fpu_etc.c
+++ b/arch/x86/math-emu/fpu_etc.c
@@ -120,9 +120,14 @@ static void fxam(FPU_REG *st0_ptr, u_char st0tag)
 	setcc(c);
 }
 
+static void FPU_ST0_illegal(FPU_REG *st0_ptr, u_char st0_tag)
+{
+	FPU_illegal();
+}
+
 static FUNC_ST0 const fp_etc_table[] = {
-	fchs, fabs, (FUNC_ST0) FPU_illegal, (FUNC_ST0) FPU_illegal,
-	ftst_, fxam, (FUNC_ST0) FPU_illegal, (FUNC_ST0) FPU_illegal
+	fchs, fabs, FPU_ST0_illegal, FPU_ST0_illegal,
+	ftst_, fxam, FPU_ST0_illegal, FPU_ST0_illegal,
 };
 
 void FPU_etc(void)
diff --git a/arch/x86/math-emu/fpu_trig.c b/arch/x86/math-emu/fpu_trig.c
index 990d847ae902..85daf98c81c3 100644
--- a/arch/x86/math-emu/fpu_trig.c
+++ b/arch/x86/math-emu/fpu_trig.c
@@ -433,13 +433,13 @@ static void fxtract(FPU_REG *st0_ptr, u_char st0_tag)
 #endif /* PARANOID */
 }
 
-static void fdecstp(void)
+static void fdecstp(FPU_REG *st0_ptr, u_char st0_tag)
 {
 	clear_C1();
 	top--;
 }
 
-static void fincstp(void)
+static void fincstp(FPU_REG *st0_ptr, u_char st0_tag)
 {
 	clear_C1();
 	top++;
@@ -1631,7 +1631,7 @@ static void fscale(FPU_REG *st0_ptr, u_char st0_tag)
 
 static FUNC_ST0 const trig_table_a[] = {
 	f2xm1, fyl2x, fptan, fpatan,
-	fxtract, fprem1, (FUNC_ST0) fdecstp, (FUNC_ST0) fincstp
+	fxtract, fprem1, fdecstp, fincstp,
 };
 
 void FPU_triga(void)
diff --git a/arch/x86/math-emu/reg_constant.c b/arch/x86/math-emu/reg_constant.c
index 742619e94bdf..003a0b2753e6 100644
--- a/arch/x86/math-emu/reg_constant.c
+++ b/arch/x86/math-emu/reg_constant.c
@@ -108,8 +108,13 @@ static void fldz(int rc)
 
 typedef void (*FUNC_RC) (int);
 
+static void FPU_RC_illegal(int unused)
+{
+	FPU_illegal();
+}
+
 static FUNC_RC constants_table[] = {
-	fld1, fldl2t, fldl2e, fldpi, fldlg2, fldln2, fldz, (FUNC_RC) FPU_illegal
+	fld1, fldl2t, fldl2e, fldpi, fldlg2, fldln2, fldz, FPU_RC_illegal
 };
 
 void fconst(void)
-- 
2.39.2