[Request for help] issue when add relative extable support to riscv64

[Jisheng Zhang]

Hi,

Now the extable entry contains 16bytes for riscv64 -- 8bytes for the insn and
another 8bytes for the fixup. This wastes mem a bit. I think we can add
the relative extable support. A draft patch put at the end of this mail. But
I met abnormal build errors:

FATAL: modpost: The relocation at __ex_table+0x0 references
section "__ex_table" which is not executable, IOW
it is not possible for the kernel to fault
at that address.  Something is seriously wrong
and should be fixed.

I investigated this issue but didn't find any clue. Any suggestion
is appreciated!

Thanks

diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
index 445ccc97305a..57b86fd9916c 100644
--- a/arch/riscv/include/asm/Kbuild
+++ b/arch/riscv/include/asm/Kbuild
@@ -1,6 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
 generic-y += early_ioremap.h
-generic-y += extable.h
 generic-y += flat.h
 generic-y += kvm_para.h
 generic-y += user.h
diff --git a/arch/riscv/include/asm/futex.h b/arch/riscv/include/asm/futex.h
index 1b00badb9f87..b220b8387c9d 100644
--- a/arch/riscv/include/asm/futex.h
+++ b/arch/riscv/include/asm/futex.h
@@ -31,8 +31,8 @@
 	"	jump 2b,%[t]				\n"	\
 	"	.previous				\n"	\
 	"	.section __ex_table,\"a\"		\n"	\
-	"	.balign " RISCV_SZPTR "			\n"	\
-	"	" RISCV_PTR " 1b, 3b			\n"	\
+	"	.balign 4			\n"	\
+	"	.word (1b-.), (3b-.)			\n"	\
 	"	.previous				\n"	\
 	: [r] "+r" (ret), [ov] "=&r" (oldval),			\
 	  [u] "+m" (*uaddr), [t] "=&r" (tmp)			\
@@ -104,9 +104,9 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 	"	jump 3b,%[t]				\n"
 	"	.previous				\n"
 	"	.section __ex_table,\"a\"		\n"
-	"	.balign " RISCV_SZPTR "			\n"
-	"	" RISCV_PTR " 1b, 4b			\n"
-	"	" RISCV_PTR " 2b, 4b			\n"
+	"	.balign 4 			\n"
+	"	.word (1b-.), (4b-.)			\n"
+	"	.word (2b-.), (4b-.)			\n"
 	"	.previous				\n"
 	: [r] "+r" (ret), [v] "=&r" (val), [u] "+m" (*uaddr), [t] "=&r" (tmp)
 	: [ov] "Jr" (oldval), [nv] "Jr" (newval), [e] "i" (-EFAULT)
diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
index f314ff44c48d..097ed3df9b17 100644
--- a/arch/riscv/include/asm/uaccess.h
+++ b/arch/riscv/include/asm/uaccess.h
@@ -94,8 +94,8 @@ do {								\
 		"	jump 2b, %2\n"				\
 		"	.previous\n"				\
 		"	.section __ex_table,\"a\"\n"		\
-		"	.balign " RISCV_SZPTR "\n"			\
-		"	" RISCV_PTR " 1b, 3b\n"			\
+		"	.balign 4 \n"			\
+		"	.word (1b - .), (3b - .)\n"			\
 		"	.previous"				\
 		: "+r" (err), "=&r" (__x), "=r" (__tmp)		\
 		: "m" (*(ptr)), "i" (-EFAULT));			\
@@ -126,9 +126,9 @@ do {								\
 		"	jump 3b, %3\n"				\
 		"	.previous\n"				\
 		"	.section __ex_table,\"a\"\n"		\
-		"	.balign " RISCV_SZPTR "\n"			\
-		"	" RISCV_PTR " 1b, 4b\n"			\
-		"	" RISCV_PTR " 2b, 4b\n"			\
+		"	.balign 4 \n"			\
+		"	.word (1b - .), (4b - .)\n"			\
+		"	.word (2b - .), (4b - .)\n"			\
 		"	.previous"				\
 		: "+r" (err), "=&r" (__lo), "=r" (__hi),	\
 			"=r" (__tmp)				\
@@ -234,8 +234,8 @@ do {								\
 		"	jump 2b, %1\n"				\
 		"	.previous\n"				\
 		"	.section __ex_table,\"a\"\n"		\
-		"	.balign " RISCV_SZPTR "\n"			\
-		"	" RISCV_PTR " 1b, 3b\n"			\
+		"	.balign 4 \n"			\
+		"	.word (1b - .), (3b - .)\n"			\
 		"	.previous"				\
 		: "+r" (err), "=r" (__tmp), "=m" (*(ptr))	\
 		: "rJ" (__x), "i" (-EFAULT));			\
@@ -263,9 +263,9 @@ do {								\
 		"	jump 3b, %1\n"				\
 		"	.previous\n"				\
 		"	.section __ex_table,\"a\"\n"		\
-		"	.balign " RISCV_SZPTR "\n"			\
-		"	" RISCV_PTR " 1b, 4b\n"			\
-		"	" RISCV_PTR " 2b, 4b\n"			\
+		"	.balign 4 \n"			\
+		"	.word (1b - .), (4b - .)\n"			\
+		"	.word (2b - .), (4b - .)\n"			\
 		"	.previous"				\
 		: "+r" (err), "=r" (__tmp),			\
 			"=m" (__ptr[__LSW]),			\
@@ -418,8 +418,8 @@ unsigned long __must_check clear_user(void __user *to, unsigned long n)
 		"	jump 1b, %[rc]\n"			\
 		".previous\n"					\
 		".section __ex_table,\"a\"\n"			\
-		".balign " RISCV_SZPTR "\n"			\
-		"	" RISCV_PTR " 1b, 2b\n"			\
+		".balign 4 \n"			\
+		".word (1b-.), (2b-.)\n"			\
 		".previous\n"					\
 			: [ret] "=&r" (__ret),			\
 			  [rc]  "=&r" (__rc),			\
@@ -444,8 +444,8 @@ unsigned long __must_check clear_user(void __user *to, unsigned long n)
 		"	jump 1b, %[rc]\n"			\
 		".previous\n"					\
 		".section __ex_table,\"a\"\n"			\
-		".balign " RISCV_SZPTR "\n"			\
-		"	" RISCV_PTR " 1b, 2b\n"			\
+		".balign 4 \n"			\
+		".word (1b-.), (2b-.)\n"			\
 		".previous\n"					\
 			: [ret] "=&r" (__ret),			\
 			  [rc]  "=&r" (__rc),			\
diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S
index 63bc691cff91..b346ecb2a051 100644
--- a/arch/riscv/lib/uaccess.S
+++ b/arch/riscv/lib/uaccess.S
@@ -7,8 +7,8 @@
 100:
 	\op \reg, \addr
 	.section __ex_table,"a"
-	.balign RISCV_SZPTR
-	RISCV_PTR 100b, \lbl
+	.balign 4
+	.word (100b - .), (\lbl - .)
 	.previous
 	.endm
 
diff --git a/arch/riscv/mm/extable.c b/arch/riscv/mm/extable.c
index 2fc729422151..6aa8ffac4be7 100644
--- a/arch/riscv/mm/extable.c
+++ b/arch/riscv/mm/extable.c
@@ -17,7 +17,7 @@ int fixup_exception(struct pt_regs *regs)
 
 	fixup = search_exception_tables(regs->epc);
 	if (fixup) {
-		regs->epc = fixup->fixup;
+		regs->epc = (unsigned long)&fixup->fixup + fixup->fixup;
 		return 1;
 	}
 	return 0;