powerpc/signal: Don't manage floating point regs when no FPU

There is no point in copying floating point regs when there
is no FPU and MATH_EMULATION is not selected.

Create a new CONFIG_PPC_FPU_REGS bool that is selected by
CONFIG_MATH_EMULATION and CONFIG_PPC_FPU, and use it to
opt out everything related to fp_state in thread_struct.

The asm const used only by fpu.S are opted out with CONFIG_PPC_FPU
as fpu.S build is conditionnal to CONFIG_PPC_FPU.

The following app spends approx 8.1 seconds system time on an 8xx
without the patch, and 7.0 seconds with the patch (13.5% reduction).

On an 832x, it spends approx 2.6 seconds system time without
the patch and 2.1 seconds with the patch (19% reduction).

	void sigusr1(int sig) { }

	int main(int argc, char **argv)
	{
		int i = 100000;

		signal(SIGUSR1, sigusr1);
		for (;i--;)
			raise(SIGUSR1);
		exit(0);
	}

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/7569070083e6cd5b279bb5023da601aba3c06f3c.1597770847.git.christophe.leroy@csgroup.eu

3 files changed, 18 insertions, 2 deletions

diff --git a/arch/powerpc/kernel/ptrace/Makefile b/arch/powerpc/kernel/ptrace/Makefile
index 77abd1a5a508..8ebc11d1168d 100644
--- a/arch/powerpc/kernel/ptrace/Makefile
+++ b/arch/powerpc/kernel/ptrace/Makefile
@@ -6,11 +6,11 @@
 CFLAGS_ptrace-view.o		+= -DUTS_MACHINE='"$(UTS_MACHINE)"'
 
 obj-y				+= ptrace.o ptrace-view.o
-obj-y				+= ptrace-fpu.o
+obj-$(CONFIG_PPC_FPU_REGS)	+= ptrace-fpu.o
 obj-$(CONFIG_COMPAT)		+= ptrace32.o
 obj-$(CONFIG_VSX)		+= ptrace-vsx.o
 ifneq ($(CONFIG_VSX),y)
-obj-y				+= ptrace-novsx.o
+obj-$(CONFIG_PPC_FPU_REGS)	+= ptrace-novsx.o
 endif
 obj-$(CONFIG_ALTIVEC)		+= ptrace-altivec.o
 obj-$(CONFIG_SPE)		+= ptrace-spe.o
diff --git a/arch/powerpc/kernel/ptrace/ptrace-decl.h b/arch/powerpc/kernel/ptrace/ptrace-decl.h
index eafe5f0f6289..3487f2c9735c 100644
--- a/arch/powerpc/kernel/ptrace/ptrace-decl.h
+++ b/arch/powerpc/kernel/ptrace/ptrace-decl.h
@@ -165,8 +165,22 @@ int ptrace_put_reg(struct task_struct *task, int regno, unsigned long data);
 extern const struct user_regset_view user_ppc_native_view;
 
 /* ptrace-fpu */
+#ifdef CONFIG_PPC_FPU_REGS
 int ptrace_get_fpr(struct task_struct *child, int index, unsigned long *data);
 int ptrace_put_fpr(struct task_struct *child, int index, unsigned long data);
+#else
+static inline int
+ptrace_get_fpr(struct task_struct *child, int index, unsigned long *data)
+{
+	return -EIO;
+}
+
+static inline int
+ptrace_put_fpr(struct task_struct *child, int index, unsigned long data)
+{
+	return -EIO;
+}
+#endif
 
 /* ptrace-(no)adv */
 void ppc_gethwdinfo(struct ppc_debug_info *dbginfo);
diff --git a/arch/powerpc/kernel/ptrace/ptrace-view.c b/arch/powerpc/kernel/ptrace/ptrace-view.c
index 142d58337f40..00a765f00d31 100644
--- a/arch/powerpc/kernel/ptrace/ptrace-view.c
+++ b/arch/powerpc/kernel/ptrace/ptrace-view.c
@@ -521,11 +521,13 @@ static const struct user_regset native_regsets[] = {
 		.size = sizeof(long), .align = sizeof(long),
 		.regset_get = gpr_get, .set = gpr_set
 	},
+#ifdef CONFIG_PPC_FPU_REGS
 	[REGSET_FPR] = {
 		.core_note_type = NT_PRFPREG, .n = ELF_NFPREG,
 		.size = sizeof(double), .align = sizeof(double),
 		.regset_get = fpr_get, .set = fpr_set
 	},
+#endif
 #ifdef CONFIG_ALTIVEC
 	[REGSET_VMX] = {
 		.core_note_type = NT_PPC_VMX, .n = 34,