ARM: kprobes: Fix build error in test code

When compiling kprobes-test-thumb.c an error like below may occur:

/tmp/ccKcuJcG.s:19179: Error: offset out of range

This is caused by the compiler underestimating the size of the inline assembler instructions containing ".space 0x1000" and failing to spill the literal pool in time to prevent the generation of PC relative load instruction with invalid offsets.

The fix implemented by this patch is to replace a single large .space directive by a number of 4 byte .space's. This requires splitting the macros which generate test cases for branch instructions into two forms:
one with, and one without support for inserting extra code between branch and target.

Signed-off-by Jon Medhurst <[email protected]>

---

 arch/arm/kernel/kprobes-test.h       |  100 ++++++++++++++++++++++++----------
 arch/arm/kernel/kprobes-test-thumb.c |   16 +++---
 2 files changed, 78 insertions(+), 38 deletions(-)

arch/arm/kernel/kprobes-test.h +70 -30

index 0dc5d77..e28a869 100644
@@ -149,23 +149,31 @@ struct test_arg_end {
 	"1:	"instruction"				\n\t"	\
 	"	nop					\n\t"
 
-#define TEST_BRANCH_F(instruction, xtra_dist)			\
+#define TEST_BRANCH_F(instruction)				\
 	TEST_INSTRUCTION(instruction)				\
-	".if "#xtra_dist"				\n\t"	\
 	"	b	99f				\n\t"	\
-	".space "#xtra_dist"				\n\t"	\
-	".endif						\n\t"	\
+	"2:	nop					\n\t"
+
+#define TEST_BRANCH_B(instruction)				\
+	"	b	50f				\n\t"	\
+	"	b	99f				\n\t"	\
+	"2:	nop					\n\t"	\
+	"	b	99f				\n\t"	\
+	TEST_INSTRUCTION(instruction)
+
+#define TEST_BRANCH_FX(instruction, codex)			\
+	TEST_INSTRUCTION(instruction)				\
+	"	b	99f				\n\t"	\
+	codex"						\n\t"	\
 	"	b	99f				\n\t"	\
 	"2:	nop					\n\t"
 
-#define TEST_BRANCH_B(instruction, xtra_dist)			\
+#define TEST_BRANCH_BX(instruction, codex)			\
 	"	b	50f				\n\t"	\
 	"	b	99f				\n\t"	\
 	"2:	nop					\n\t"	\
 	"	b	99f				\n\t"	\
-	".if "#xtra_dist"				\n\t"	\
-	".space "#xtra_dist"				\n\t"	\
-	".endif						\n\t"	\
+	codex"						\n\t"	\
 	TEST_INSTRUCTION(instruction)
 
 #define TESTCASE_END						\

@@ -301,47 +309,60 @@ struct test_arg_end {
 	TESTCASE_START(code1 #reg1 code2)	\
 	TEST_ARG_PTR(reg1, val1)		\
 	TEST_ARG_END("")			\
-	TEST_BRANCH_F(code1 #reg1 code2, 0)	\
+	TEST_BRANCH_F(code1 #reg1 code2)	\
 	TESTCASE_END
 
-#define TEST_BF_X(code, xtra_dist)		\
+#define TEST_BF(code)				\
 	TESTCASE_START(code)			\
 	TEST_ARG_END("")			\
-	TEST_BRANCH_F(code, xtra_dist)		\
+	TEST_BRANCH_F(code)			\
 	TESTCASE_END
 
-#define TEST_BB_X(code, xtra_dist)		\
+#define TEST_BB(code)				\
 	TESTCASE_START(code)			\
 	TEST_ARG_END("")			\
-	TEST_BRANCH_B(code, xtra_dist)		\
+	TEST_BRANCH_B(code)			\
 	TESTCASE_END
 
-#define TEST_BF_RX(code1, reg, val, code2, xtra_dist)	\
-	TESTCASE_START(code1 #reg code2)		\
-	TEST_ARG_REG(reg, val)				\
-	TEST_ARG_END("")				\
-	TEST_BRANCH_F(code1 #reg code2, xtra_dist)	\
+#define TEST_BF_R(code1, reg, val, code2)	\
+	TESTCASE_START(code1 #reg code2)	\
+	TEST_ARG_REG(reg, val)			\
+	TEST_ARG_END("")			\
+	TEST_BRANCH_F(code1 #reg code2)		\
 	TESTCASE_END
 
-#define TEST_BB_RX(code1, reg, val, code2, xtra_dist)	\
-	TESTCASE_START(code1 #reg code2)		\
-	TEST_ARG_REG(reg, val)				\
-	TEST_ARG_END("")				\
-	TEST_BRANCH_B(code1 #reg code2, xtra_dist)	\
+#define TEST_BB_R(code1, reg, val, code2)	\
+	TESTCASE_START(code1 #reg code2)	\
+	TEST_ARG_REG(reg, val)			\
+	TEST_ARG_END("")			\
+	TEST_BRANCH_B(code1 #reg code2)		\
 	TESTCASE_END
 
-#define TEST_BF(code)	TEST_BF_X(code, 0)
-#define TEST_BB(code)	TEST_BB_X(code, 0)
-
-#define TEST_BF_R(code1, reg, val, code2) TEST_BF_RX(code1, reg, val, code2, 0)
-#define TEST_BB_R(code1, reg, val, code2) TEST_BB_RX(code1, reg, val, code2, 0)
-
 #define TEST_BF_RR(code1, reg1, val1, code2, reg2, val2, code3)	\
 	TESTCASE_START(code1 #reg1 code2 #reg2 code3)		\
 	TEST_ARG_REG(reg1, val1)				\
 	TEST_ARG_REG(reg2, val2)				\
 	TEST_ARG_END("")					\
-	TEST_BRANCH_F(code1 #reg1 code2 #reg2 code3, 0)		\
+	TEST_BRANCH_F(code1 #reg1 code2 #reg2 code3)		\
+	TESTCASE_END
+
+#define TEST_BF_X(code, codex)			\
+	TESTCASE_START(code)			\
+	TEST_ARG_END("")			\
+	TEST_BRANCH_FX(code, codex)		\
+	TESTCASE_END
+
+#define TEST_BB_X(code, codex)			\
+	TESTCASE_START(code)			\
+	TEST_ARG_END("")			\
+	TEST_BRANCH_BX(code, codex)		\
+	TESTCASE_END
+
+#define TEST_BF_RX(code1, reg, val, code2, codex)	\
+	TESTCASE_START(code1 #reg code2)		\
+	TEST_ARG_REG(reg, val)				\
+	TEST_ARG_END("")				\
+	TEST_BRANCH_FX(code1 #reg code2, codex)		\
 	TESTCASE_END
 
 #define TEST_X(code, codex)			\

@@ -372,6 +393,25 @@ struct test_arg_end {
 	TESTCASE_END
 
 
+/*
+ * Macros for defining space directives spread over multiple lines.
+ * These are required so the compiler guesses better the length of inline asm
+ * code and will spill the literal pool early enough to avoid generating PC
+ * relative loads with out of range offsets.
+ */
+#define TWICE(x)	x x
+#define SPACE_0x8	TWICE(".space 4\n\t")
+#define SPACE_0x10	TWICE(SPACE_0x8)
+#define SPACE_0x20	TWICE(SPACE_0x10)
+#define SPACE_0x40	TWICE(SPACE_0x20)
+#define SPACE_0x80	TWICE(SPACE_0x40)
+#define SPACE_0x100	TWICE(SPACE_0x80)
+#define SPACE_0x200	TWICE(SPACE_0x100)
+#define SPACE_0x400	TWICE(SPACE_0x200)
+#define SPACE_0x800	TWICE(SPACE_0x400)
+#define SPACE_0x1000	TWICE(SPACE_0x800)
+
+
 /* Various values used in test cases... */
 #define N(val)	(val ^ 0xffffffff)
 #define VAL1	0x12345678

arch/arm/kernel/kprobes-test-thumb.c +8 -8

index 5e726c3..5d8b857 100644
@@ -222,8 +222,8 @@ void kprobe_thumb16_test_cases(void)
 DONT_TEST_IN_ITBLOCK(
 	TEST_BF_R(  "cbnz	r",0,0, ", 2f")
 	TEST_BF_R(  "cbz	r",2,-1,", 2f")
-	TEST_BF_RX( "cbnz	r",4,1, ", 2f",0x20)
-	TEST_BF_RX( "cbz	r",7,0, ", 2f",0x40)
+	TEST_BF_RX( "cbnz	r",4,1, ", 2f", SPACE_0x20)
+	TEST_BF_RX( "cbz	r",7,0, ", 2f", SPACE_0x40)
 )
 	TEST_R("sxth	r0, r",7, HH1,"")
 	TEST_R("sxth	r7, r",0, HH2,"")

@@ -246,7 +246,7 @@ DONT_TEST_IN_ITBLOCK(
 	TESTCASE_START(code)		\
 	TEST_ARG_PTR(13, offset)	\
 	TEST_ARG_END("")		\
-	TEST_BRANCH_F(code,0)		\
+	TEST_BRANCH_F(code)		\
 	TESTCASE_END
 
 	TEST("push	{r0}")

@@ -319,8 +319,8 @@ CONDITION_INSTRUCTIONS(8,
 
 	TEST_BF(  "b	2f")
 	TEST_BB(  "b	2b")
-	TEST_BF_X("b	2f", 0x400)
-	TEST_BB_X("b	2b", 0x400)
+	TEST_BF_X("b	2f", SPACE_0x400)
+	TEST_BB_X("b	2b", SPACE_0x400)
 
 	TEST_GROUP("Testing instructions in IT blocks")
 

@@ -746,7 +746,7 @@ CONDITION_INSTRUCTIONS(22,
 	TEST_BB("bne.w	2b")
 	TEST_BF("bgt.w	2f")
 	TEST_BB("blt.w	2b")
-	TEST_BF_X("bpl.w	2f",0x1000)
+	TEST_BF_X("bpl.w	2f", SPACE_0x1000)
 )
 
 	TEST_UNSUPPORTED("msr	cpsr, r0")

@@ -786,11 +786,11 @@ CONDITION_INSTRUCTIONS(22,
 
 	TEST_BF(  "b.w	2f")
 	TEST_BB(  "b.w	2b")
-	TEST_BF_X("b.w	2f", 0x1000)
+	TEST_BF_X("b.w	2f", SPACE_0x1000)
 
 	TEST_BF(  "bl.w	2f")
 	TEST_BB(  "bl.w	2b")
-	TEST_BB_X("bl.w	2b", 0x1000)
+	TEST_BB_X("bl.w	2b", SPACE_0x1000)
 
 	TEST_X(	"blx	__dummy_arm_subroutine",
 		".arm				\n\t"

Quoted 15 lines · Jon Medhurst (Tixy)

When compiling kprobes-test-thumb.c an error like below may occur:

/tmp/ccKcuJcG.s:19179: Error: offset out of range

This is caused by the compiler underestimating the size of the inline assembler instructions containing ".space 0x1000" and failing to spill the literal pool in time to prevent the generation of PC relative load instruction with invalid offsets.

The fix implemented by this patch is to replace a single large .space directive by a number of 4 byte .space's. This requires splitting the macros which generate test cases for branch instructions into two forms:
one with, and one without support for inserting extra code between branch and target.

Quoted 2 lines

Signed-off-by Jon Medhurst <[email protected]>

---

Nicolas, I noticed that you put this patch into the Linaro kernel tree, can I take that as an Acked-by? ;-)