powerpc/lib: Add alt patching test of branching past the last instruction

Add a test of the relative branch patching logic in the alternate
section feature fixup code. This tests that if we branch past the last
instruction of the alternate section, the branch is not patched.
That's because the assembler will have created a branch that already
points to the first instruction after the patched section, which is
correct and needs no further patching.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/lib/feature-fixups-test.S

@@ -171,6 +171,42 @@ globl(ftr_fixup_test6_expected)
 	or	2,2,2
 	or	3,3,3
 
+globl(ftr_fixup_test7)
+	or	1,1,1
+BEGIN_FTR_SECTION
+	or	2,2,2
+	or	2,2,2
+	or	2,2,2
+	or	2,2,2
+	or	2,2,2
+	or	2,2,2
+	or	2,2,2
+FTR_SECTION_ELSE
+2:	b	3f
+3:	or	5,5,5
+	beq	3b
+	b	1f
+	or	6,6,6
+	b	2b
+	bdnz	3b
+1:
+ALT_FTR_SECTION_END(0, 1)
+	or	1,1,1
+	or	1,1,1
+
+globl(end_ftr_fixup_test7)
+	nop
+
+globl(ftr_fixup_test7_expected)
+	or	1,1,1
+2:	b	3f
+3:	or	5,5,5
+	beq	3b
+	b	1f
+	or	6,6,6
+	b	2b
+	bdnz	3b
+1:	or	1,1,1
 
 #if 0
 /* Test that if we have a larger else case the assembler spots it and

arch/powerpc/lib/feature-fixups.c

@@ -425,6 +425,16 @@ static void test_alternative_case_with_external_branch(void)
 	check(memcmp(ftr_fixup_test6, ftr_fixup_test6_expected, size) == 0);
 }
 
+static void test_alternative_case_with_branch_to_end(void)
+{
+	extern unsigned int ftr_fixup_test7[];
+	extern unsigned int end_ftr_fixup_test7[];
+	extern unsigned int ftr_fixup_test7_expected[];
+	int size = 4 * (end_ftr_fixup_test7 - ftr_fixup_test7);
+
+	check(memcmp(ftr_fixup_test7, ftr_fixup_test7_expected, size) == 0);
+}
+
 static void test_cpu_macros(void)
 {
 	extern u8 ftr_fixup_test_FTR_macros[];
@@ -480,6 +490,7 @@ static int __init test_feature_fixups(void)
 	test_alternative_case_too_small();
 	test_alternative_case_with_branch();
 	test_alternative_case_with_external_branch();
+	test_alternative_case_with_branch_to_end();
 	test_cpu_macros();
 	test_fw_macros();
 	test_lwsync_macros();