powerpc: Ensure the else case of feature sections will fit

When we create an alternative feature section, the else case must be the
same size or smaller than the body. This is because when we patch the
else case in we just overwrite the body, so there must be room.

Up to now we just did this by inspection, but it's quite easy to enforce
it in the assembler, so we should.

The only change is to add the ifgt block, but that effects the alignment
of the tabs and so the whole macro is modified.

Also add a test, but #if 0 it because we don't want to break the build.
Anyone who's modifying the feature macros should enable the test.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/include/asm/feature-fixups.h b/arch/powerpc/include/asm/feature-fixups.h
index 96a7d067fbb260ce03f0d03a8163a3d755d4c08a..921a8470e18a591b70c88ad6796a08ee0c6a588c 100644 (file)
--- a/arch/powerpc/include/asm/feature-fixups.h
+++ b/arch/powerpc/include/asm/feature-fixups.h
@@ -37,18 +37,21 @@ label##2:                                           \
        .align 2;                                       \
 label##3:
 
-#define MAKE_FTR_SECTION_ENTRY(msk, val, label, sect)  \
-label##4:                                              \
-       .popsection;                                    \
-       .pushsection sect,"a";                          \
-       .align 3;                                       \
-label##5:                                              \
-       FTR_ENTRY_LONG msk;                             \
-       FTR_ENTRY_LONG val;                             \
-       FTR_ENTRY_OFFSET label##1b-label##5b;           \
-       FTR_ENTRY_OFFSET label##2b-label##5b;           \
-       FTR_ENTRY_OFFSET label##3b-label##5b;           \
-       FTR_ENTRY_OFFSET label##4b-label##5b;           \
+#define MAKE_FTR_SECTION_ENTRY(msk, val, label, sect)          \
+label##4:                                                      \
+       .popsection;                                            \
+       .pushsection sect,"a";                                  \
+       .align 3;                                               \
+label##5:                                                      \
+       FTR_ENTRY_LONG msk;                                     \
+       FTR_ENTRY_LONG val;                                     \
+       FTR_ENTRY_OFFSET label##1b-label##5b;                   \
+       FTR_ENTRY_OFFSET label##2b-label##5b;                   \
+       FTR_ENTRY_OFFSET label##3b-label##5b;                   \
+       FTR_ENTRY_OFFSET label##4b-label##5b;                   \
+       .ifgt (label##4b-label##3b)-(label##2b-label##1b);      \
+       .error "Feature section else case larger than body";    \
+       .endif;                                                 \
        .popsection;
 
 

diff --git a/arch/powerpc/lib/feature-fixups-test.S b/arch/powerpc/lib/feature-fixups-test.S
index cb737484c5aa2aa74f38df054143b208c4d74312..f4613118132e51235f38cd831ec3cfaf8417d680 100644 (file)
--- a/arch/powerpc/lib/feature-fixups-test.S
+++ b/arch/powerpc/lib/feature-fixups-test.S
@@ -172,6 +172,25 @@ globl(ftr_fixup_test6_expected)
 3:     or      3,3,3
 
 
+#if 0
+/* Test that if we have a larger else case the assembler spots it and
+ * reports an error. #if 0'ed so as not to break the build normally.
+ */
+ftr_fixup_test7:
+       or      1,1,1
+BEGIN_FTR_SECTION
+       or      2,2,2
+       or      2,2,2
+       or      2,2,2
+FTR_SECTION_ELSE
+       or      3,3,3
+       or      3,3,3
+       or      3,3,3
+       or      3,3,3
+ALT_FTR_SECTION_END(0, 1)
+       or      1,1,1
+#endif
+
 #define        MAKE_MACRO_TEST(TYPE)                                           \
 globl(ftr_fixup_test_ ##TYPE##_macros)                                 \
        or      1,1,1;                                                  \