MIPS: relocatable: optimize the relocation process

For now, vmlinux relocation functions for relocatable kernel are
implemented as an array of handlers of a particular type.

Convert that array into a single switch-case function to:
 - remove unused arguments;
 - change the return type of simple handlers to void;
 - remove the array and don't use any data at all;
 - avoid using indirect calls;
 - allow the compiler to inline and greatly optimize
   the relocation function[s];

and also mark do_relocations() and show_kernel_relocation() static
as they aren't used anywhere else.

The result on MIPS32 R2 with GCC 10.2 -O2 is:

scripts/bloat-o-meter -c arch/mips/kernel/__relocate.o arch/mips/kernel/relocate.o
add/remove: 0/6 grow/shrink: 1/0 up/down: 356/-640 (-284)
Function                                     old     new   delta
relocate_kernel                              852    1208    +356
apply_r_mips_32_rel                           20       -     -20
apply_r_mips_hi16_rel                         40       -     -40
apply_r_mips_64_rel                           44       -     -44
apply_r_mips_26_rel                          144       -    -144
show_kernel_relocation                       164       -    -164
do_relocations                               228       -    -228
Total: Before=1780, After=1496, chg -15.96%
add/remove: 0/1 grow/shrink: 0/0 up/down: 0/-76 (-76)
Data                                         old     new   delta
reloc_handlers_rel                            76       -     -76
Total: Before=92, After=16, chg -82.61%
add/remove: 0/0 grow/shrink: 0/0 up/down: 0/0 (0)
RO Data                                      old     new   delta
Total: Before=0, After=0, chg +0.00%

All functions were collapsed into the main one, relocate_kernel().

Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/kernel/relocate.c

@@ -70,18 +70,14 @@ static void __init sync_icache(void *kbase, unsigned long kernel_length)
 	__sync();
 }
 
-static int __init apply_r_mips_64_rel(u32 *loc_orig, u32 *loc_new, long offset)
+static void __init apply_r_mips_64_rel(u32 *loc_new, long offset)
 {
 	*(u64 *)loc_new += offset;
-
-	return 0;
 }
 
-static int __init apply_r_mips_32_rel(u32 *loc_orig, u32 *loc_new, long offset)
+static void __init apply_r_mips_32_rel(u32 *loc_new, long offset)
 {
 	*loc_new += offset;
-
-	return 0;
 }
 
 static int __init apply_r_mips_26_rel(u32 *loc_orig, u32 *loc_new, long offset)
@@ -114,25 +110,42 @@ static int __init apply_r_mips_26_rel(u32 *loc_orig, u32 *loc_new, long offset)
 }
 
 
-static int __init apply_r_mips_hi16_rel(u32 *loc_orig, u32 *loc_new, long offset)
+static void __init apply_r_mips_hi16_rel(u32 *loc_orig, u32 *loc_new,
+					 long offset)
 {
 	unsigned long insn = *loc_orig;
 	unsigned long target = (insn & 0xffff) << 16; /* high 16bits of target */
 
 	target += offset;
 
 	*loc_new = (insn & ~0xffff) | ((target >> 16) & 0xffff);
-	return 0;
 }
 
-static int (*reloc_handlers_rel[]) (u32 *, u32 *, long) __initdata = {
-	[R_MIPS_64]		= apply_r_mips_64_rel,
-	[R_MIPS_32]		= apply_r_mips_32_rel,
-	[R_MIPS_26]		= apply_r_mips_26_rel,
-	[R_MIPS_HI16]		= apply_r_mips_hi16_rel,
-};
+static int __init reloc_handler(u32 type, u32 *loc_orig, u32 *loc_new,
+				long offset)
+{
+	switch (type) {
+	case R_MIPS_64:
+		apply_r_mips_64_rel(loc_new, offset);
+		break;
+	case R_MIPS_32:
+		apply_r_mips_32_rel(loc_new, offset);
+		break;
+	case R_MIPS_26:
+		return apply_r_mips_26_rel(loc_orig, loc_new, offset);
+	case R_MIPS_HI16:
+		apply_r_mips_hi16_rel(loc_orig, loc_new, offset);
+		break;
+	default:
+		pr_err("Unhandled relocation type %d at 0x%pK\n", type,
+		       loc_orig);
+		return -ENOEXEC;
+	}
 
-int __init do_relocations(void *kbase_old, void *kbase_new, long offset)
+	return 0;
+}
+
+static int __init do_relocations(void *kbase_old, void *kbase_new, long offset)
 {
 	u32 *r;
 	u32 *loc_orig;
@@ -149,14 +162,7 @@ int __init do_relocations(void *kbase_old, void *kbase_new, long offset)
 		loc_orig = kbase_old + ((*r & 0x00ffffff) << 2);
 		loc_new = RELOCATED(loc_orig);
 
-		if (reloc_handlers_rel[type] == NULL) {
-			/* Unsupported relocation */
-			pr_err("Unhandled relocation type %d at 0x%pK\n",
-			       type, loc_orig);
-			return -ENOEXEC;
-		}
-
-		res = reloc_handlers_rel[type](loc_orig, loc_new, offset);
+		res = reloc_handler(type, loc_orig, loc_new, offset);
 		if (res)
 			return res;
 	}
@@ -412,7 +418,7 @@ void *__init relocate_kernel(void)
 /*
  * Show relocation information on panic.
  */
-void show_kernel_relocation(const char *level)
+static void show_kernel_relocation(const char *level)
 {
 	unsigned long offset;