selftests/powerpc: Fix error handling in FPU/VMX preemption tests

The FPU & VMX preemption tests do not check for errors returned by the
low-level asm routines, preempt_fpu() / preempt_vsx() respectively.
That means any register corruption detected by the asm routines does not
result in a test failure.

Fix it by returning the return value of the asm routines from the
pthread child routines.

Fixes: e5ab8be ("selftests/powerpc: Test preservation of FPU and VMX regs across preemption")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231128132748.1990179-1-mpe@ellerman.id.au

tools/testing/selftests/powerpc/math/fpu_preempt.c

@@ -37,19 +37,20 @@ __thread double darray[] = {0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0,
 int threads_starting;
 int running;
 
-extern void preempt_fpu(double *darray, int *threads_starting, int *running);
+extern int preempt_fpu(double *darray, int *threads_starting, int *running);
 
 void *preempt_fpu_c(void *p)
 {
+	long rc;
 	int i;
+
 	srand(pthread_self());
 	for (i = 0; i < 21; i++)
 		darray[i] = rand();
 
-	/* Test failed if it ever returns */
-	preempt_fpu(darray, &threads_starting, &running);
+	rc = preempt_fpu(darray, &threads_starting, &running);
 
-	return p;
+	return (void *)rc;
 }
 
 int test_preempt_fpu(void)

tools/testing/selftests/powerpc/math/vmx_preempt.c

@@ -37,19 +37,21 @@ __thread vector int varray[] = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10,11,12},
 int threads_starting;
 int running;
 
-extern void preempt_vmx(vector int *varray, int *threads_starting, int *running);
+extern int preempt_vmx(vector int *varray, int *threads_starting, int *running);
 
 void *preempt_vmx_c(void *p)
 {
 	int i, j;
+	long rc;
+
 	srand(pthread_self());
 	for (i = 0; i < 12; i++)
 		for (j = 0; j < 4; j++)
 			varray[i][j] = rand();
 
-	/* Test fails if it ever returns */
-	preempt_vmx(varray, &threads_starting, &running);
-	return p;
+	rc = preempt_vmx(varray, &threads_starting, &running);
+
+	return (void *)rc;
 }
 
 int test_preempt_vmx(void)