powerpc: Switch to relative jump labels

Convert powerpc to relative jump labels.

Before the patch, pseries_defconfig vmlinux.o has:
9074 __jump_table  0003f2a0  0000000000000000  0000000000000000  01321fa8  2**0

With the patch, the same config gets:
9074 __jump_table  0002a0e0  0000000000000000  0000000000000000  01321fb4  2**0

Size is 258720 without the patch, 172256 with the patch.
That's a 33% size reduction.

Largely copied from commit c296146c ("arm64/kernel: jump_label:
Switch to relative references")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/828348da7868eda953ce023994404dfc49603b64.1616514473.git.christophe.leroy@csgroup.eu

arch/powerpc/Kconfig

@@ -184,6 +184,7 @@ config PPC
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_HUGE_VMAP		if PPC_BOOK3S_64 && PPC_RADIX_MMU
 	select HAVE_ARCH_JUMP_LABEL
+	select HAVE_ARCH_JUMP_LABEL_RELATIVE
 	select HAVE_ARCH_KASAN			if PPC32 && PPC_PAGE_SHIFT <= 14
 	select HAVE_ARCH_KASAN_VMALLOC		if PPC32 && PPC_PAGE_SHIFT <= 14
 	select HAVE_ARCH_KGDB

arch/powerpc/include/asm/jump_label.h

@@ -20,7 +20,8 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
 	asm_volatile_goto("1:\n\t"
 		 "nop # arch_static_branch\n\t"
 		 ".pushsection __jump_table,  \"aw\"\n\t"
-		 JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
+		 ".long 1b - ., %l[l_yes] - .\n\t"
+		 JUMP_ENTRY_TYPE "%c0 - .\n\t"
 		 ".popsection \n\t"
 		 : :  "i" (&((char *)key)[branch]) : : l_yes);
 
@@ -34,7 +35,8 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
 	asm_volatile_goto("1:\n\t"
 		 "b %l[l_yes] # arch_static_branch_jump\n\t"
 		 ".pushsection __jump_table,  \"aw\"\n\t"
-		 JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
+		 ".long 1b - ., %l[l_yes] - .\n\t"
+		 JUMP_ENTRY_TYPE "%c0 - .\n\t"
 		 ".popsection \n\t"
 		 : :  "i" (&((char *)key)[branch]) : : l_yes);
 
@@ -43,23 +45,12 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
 	return true;
 }
 
-#ifdef CONFIG_PPC64
-typedef u64 jump_label_t;
-#else
-typedef u32 jump_label_t;
-#endif
-
-struct jump_entry {
-	jump_label_t code;
-	jump_label_t target;
-	jump_label_t key;
-};
-
 #else
 #define ARCH_STATIC_BRANCH(LABEL, KEY)		\
 1098:	nop;					\
 	.pushsection __jump_table, "aw";	\
-	FTR_ENTRY_LONG 1098b, LABEL, KEY;	\
+	.long 1098b - ., LABEL - .;		\
+	FTR_ENTRY_LONG KEY;			\
 	.popsection
 #endif
 

arch/powerpc/kernel/jump_label.c

@@ -11,10 +11,10 @@
 void arch_jump_label_transform(struct jump_entry *entry,
 			       enum jump_label_type type)
 {
-	struct ppc_inst *addr = (struct ppc_inst *)(unsigned long)entry->code;
+	struct ppc_inst *addr = (struct ppc_inst *)jump_entry_code(entry);
 
 	if (type == JUMP_LABEL_JMP)
-		patch_branch(addr, entry->target, 0);
+		patch_branch(addr, jump_entry_target(entry), 0);
 	else
 		patch_instruction(addr, ppc_inst(PPC_INST_NOP));
 }