[PATCH v2 02/22] ARM: add self test for runtime patch mechanism

[Cyril Chemparathy]

This patch adds basic sanity tests to ensure that the instruction patching
results in valid instruction encodings.  This is done by verifying the output
of the patch process against a vector of assembler generated instructions at
init time.

Signed-off-by: Cyril Chemparathy <cyril at ti.com>
---
 arch/arm/Kconfig                |   12 ++++++++++++
 arch/arm/kernel/runtime-patch.c |   41 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index d0a04ad..7e552dc 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -211,6 +211,18 @@ config ARM_PATCH_PHYS_VIRT
 	  this feature (eg, building a kernel for a single machine) and
 	  you need to shrink the kernel to the minimal size.
 
+config ARM_RUNTIME_PATCH_TEST
+	bool "Self test runtime patching mechanism" if ARM_RUNTIME_PATCH
+	default y
+	help
+	  Select this to enable init time self checking for the runtime kernel
+	  patching mechanism.  This enables an ISA specific set of tests that
+	  ensure that the instructions generated by the patch process are
+	  consistent with those generated by the assembler at compile time.
+
+	  Only disable this option if you need to shrink the kernel to the
+	  minimal size.
+
 config NEED_MACH_IO_H
 	bool
 	help
diff --git a/arch/arm/kernel/runtime-patch.c b/arch/arm/kernel/runtime-patch.c
index fd37a2b..c471d8c 100644
--- a/arch/arm/kernel/runtime-patch.c
+++ b/arch/arm/kernel/runtime-patch.c
@@ -163,6 +163,44 @@ static int apply_patch_imm8(const struct patch_info *p)
 	return 0;
 }
 
+#ifdef CONFIG_ARM_RUNTIME_PATCH_TEST
+static void __init __used __naked __patch_test_code_imm8(void)
+{
+	__asm__ __volatile__ (
+		"	.irp	shift1, 0, 6, 12, 18\n"
+		"	.irp	shift2, 0, 1, 2, 3, 4, 5\n"
+		"	add     r1, r2, #(0x41 << (\\shift1 + \\shift2))\n"
+		"	.endr\n"
+		"	.endr\n"
+		"	.word	0\n"
+		: : :
+	);
+}
+
+static void __init test_patch_imm8(void)
+{
+	u32 test_code_addr = (u32)(&__patch_test_code_imm8);
+	u32 *test_code = (u32 *)(test_code_addr & ~0x3);
+	int i, ret;
+	u32 ninsn, insn;
+
+	insn = test_code[0];
+	for (i = 0; test_code[i]; i++) {
+		ret = do_patch_imm8(insn, 0x41 << i, &ninsn);
+		if (ret < 0)
+			pr_err("runtime patch (imm8): failed at shift %d\n", i);
+		else if (ninsn != test_code[i])
+			pr_err("runtime patch (imm8): failed, need %x got %x\n",
+			       test_code[i], ninsn);
+	}
+}
+
+static void __init runtime_patch_test(void)
+{
+	test_patch_imm8();
+}
+#endif
+
 int runtime_patch(const void *table, unsigned size)
 {
 	const struct patch_info *p = table, *end = (table + size);
@@ -185,5 +223,8 @@ void __init runtime_patch_kernel(void)
 	const void *start = &__runtime_patch_table_begin;
 	const void *end   = &__runtime_patch_table_end;
 
+#ifdef CONFIG_ARM_RUNTIME_PATCH_TEST
+	runtime_patch_test();
+#endif
 	BUG_ON(runtime_patch(start, end - start));
 }
-- 
1.7.9.5