MIPS: module: optimize module relocations processing

For now, module relocation functions are implemented as an array
of handlers of type reloc_handler_t.

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].

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

scripts/bloat-o-meter -c arch/mips/kernel/__module.o arch/mips/kernel/module.o
add/remove: 1/11 grow/shrink: 1/0 up/down: 876/-1436 (-560)
Function                                     old     new   delta
apply_relocate                               456    1148    +692
apply_r_mips_pc                                -     184    +184
apply_r_mips_none                              8       -      -8
apply_r_mips_32                               16       -     -16
apply_r_mips_64                               76       -     -76
apply_r_mips_highest                          88       -     -88
apply_r_mips_higher                          108       -    -108
apply_r_mips_26                              132       -    -132
apply_r_mips_pc26                            160       -    -160
apply_r_mips_pc21                            160       -    -160
apply_r_mips_pc16                            160       -    -160
apply_r_mips_hi16                            172       -    -172
apply_r_mips_lo16                            356       -    -356
Total: Before=2608, After=2048, chg -21.47%
add/remove: 0/0 grow/shrink: 0/0 up/down: 0/0 (0)
Data                                         old     new   delta
Total: Before=12, After=12, chg +0.00%
add/remove: 0/1 grow/shrink: 0/0 up/down: 0/-248 (-248)
RO Data                                      old     new   delta
reloc_handlers                               248       -    -248
Total: Before=248, After=0, chg -100.00%

All functions were collapsed into a single one that is called
directly by $(srctree)/kernel/module.c.

Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

diff --git a/arch/mips/kernel/module.c b/arch/mips/kernel/module.c
index 3c0c3d1..14f46d1 100644 (file)
--- a/arch/mips/kernel/module.c
+++ b/arch/mips/kernel/module.c
@@ -40,22 +40,13 @@ void *module_alloc(unsigned long size)
 }
 #endif
 
-static int apply_r_mips_none(struct module *me, u32 *location,
-                            u32 base, Elf_Addr v, bool rela)
-{
-       return 0;
-}
-
-static int apply_r_mips_32(struct module *me, u32 *location,
-                          u32 base, Elf_Addr v, bool rela)
+static void apply_r_mips_32(u32 *location, u32 base, Elf_Addr v)
 {
        *location = base + v;
-
-       return 0;
 }
 
-static int apply_r_mips_26(struct module *me, u32 *location,
-                          u32 base, Elf_Addr v, bool rela)
+static int apply_r_mips_26(struct module *me, u32 *location, u32 base,
+                          Elf_Addr v)
 {
        if (v % 4) {
                pr_err("module %s: dangerous R_MIPS_26 relocation\n",
@@ -75,8 +66,8 @@ static int apply_r_mips_26(struct module *me, u32 *location,
        return 0;
 }
 
-static int apply_r_mips_hi16(struct module *me, u32 *location,
-                            u32 base, Elf_Addr v, bool rela)
+static int apply_r_mips_hi16(struct module *me, u32 *location, Elf_Addr v,
+                            bool rela)
 {
        struct mips_hi16 *n;
 
@@ -217,26 +208,25 @@ static int apply_r_mips_pc(struct module *me, u32 *location, u32 base,
        return 0;
 }
 
-static int apply_r_mips_pc16(struct module *me, u32 *location,
-                            u32 base, Elf_Addr v, bool rela)
+static int apply_r_mips_pc16(struct module *me, u32 *location, u32 base,
+                            Elf_Addr v)
 {
        return apply_r_mips_pc(me, location, base, v, 16);
 }
 
-static int apply_r_mips_pc21(struct module *me, u32 *location,
-                            u32 base, Elf_Addr v, bool rela)
+static int apply_r_mips_pc21(struct module *me, u32 *location, u32 base,
+                            Elf_Addr v)
 {
        return apply_r_mips_pc(me, location, base, v, 21);
 }
 
-static int apply_r_mips_pc26(struct module *me, u32 *location,
-                            u32 base, Elf_Addr v, bool rela)
+static int apply_r_mips_pc26(struct module *me, u32 *location, u32 base,
+                            Elf_Addr v)
 {
        return apply_r_mips_pc(me, location, base, v, 26);
 }
 
-static int apply_r_mips_64(struct module *me, u32 *location,
-                          u32 base, Elf_Addr v, bool rela)
+static int apply_r_mips_64(u32 *location, Elf_Addr v, bool rela)
 {
        if (WARN_ON(!rela))
                return -EINVAL;
@@ -246,8 +236,7 @@ static int apply_r_mips_64(struct module *me, u32 *location,
        return 0;
 }
 
-static int apply_r_mips_higher(struct module *me, u32 *location,
-                              u32 base, Elf_Addr v, bool rela)
+static int apply_r_mips_higher(u32 *location, Elf_Addr v, bool rela)
 {
        if (WARN_ON(!rela))
                return -EINVAL;
@@ -258,8 +247,7 @@ static int apply_r_mips_higher(struct module *me, u32 *location,
        return 0;
 }
 
-static int apply_r_mips_highest(struct module *me, u32 *location,
-                               u32 base, Elf_Addr v, bool rela)
+static int apply_r_mips_highest(u32 *location, Elf_Addr v, bool rela)
 {
        if (WARN_ON(!rela))
                return -EINVAL;
@@ -272,12 +260,14 @@ static int apply_r_mips_highest(struct module *me, u32 *location,
 
 /**
  * reloc_handler() - Apply a particular relocation to a module
+ * @type: type of the relocation to apply
  * @me: the module to apply the reloc to
  * @location: the address at which the reloc is to be applied
  * @base: the existing value at location for REL-style; 0 for RELA-style
  * @v: the value of the reloc, with addend for RELA-style
+ * @rela: indication of is this a RELA (true) or REL (false) relocation
  *
- * Each implemented reloc_handler function applies a particular type of
+ * Each implemented relocation function applies a particular type of
  * relocation to the module @me. Relocs that may be found in either REL or RELA
  * variants can be handled by making use of the @base & @v parameters which are
  * set to values which abstract the difference away from the particular reloc
@@ -285,23 +275,40 @@ static int apply_r_mips_highest(struct module *me, u32 *location,
  *
  * Return: 0 upon success, else -ERRNO
  */
-typedef int (*reloc_handler)(struct module *me, u32 *location,
-                            u32 base, Elf_Addr v, bool rela);
-
-/* The handlers for known reloc types */
-static reloc_handler reloc_handlers[] = {
-       [R_MIPS_NONE]           = apply_r_mips_none,
-       [R_MIPS_32]             = apply_r_mips_32,
-       [R_MIPS_26]             = apply_r_mips_26,
-       [R_MIPS_HI16]           = apply_r_mips_hi16,
-       [R_MIPS_LO16]           = apply_r_mips_lo16,
-       [R_MIPS_PC16]           = apply_r_mips_pc16,
-       [R_MIPS_64]             = apply_r_mips_64,
-       [R_MIPS_HIGHER]         = apply_r_mips_higher,
-       [R_MIPS_HIGHEST]        = apply_r_mips_highest,
-       [R_MIPS_PC21_S2]        = apply_r_mips_pc21,
-       [R_MIPS_PC26_S2]        = apply_r_mips_pc26,
-};
+static int reloc_handler(u32 type, struct module *me, u32 *location, u32 base,
+                        Elf_Addr v, bool rela)
+{
+       switch (type) {
+       case R_MIPS_NONE:
+               break;
+       case R_MIPS_32:
+               apply_r_mips_32(location, base, v);
+               break;
+       case R_MIPS_26:
+               return apply_r_mips_26(me, location, base, v);
+       case R_MIPS_HI16:
+               return apply_r_mips_hi16(me, location, v, rela);
+       case R_MIPS_LO16:
+               return apply_r_mips_lo16(me, location, base, v, rela);
+       case R_MIPS_PC16:
+               return apply_r_mips_pc16(me, location, base, v);
+       case R_MIPS_PC21_S2:
+               return apply_r_mips_pc21(me, location, base, v);
+       case R_MIPS_PC26_S2:
+               return apply_r_mips_pc26(me, location, base, v);
+       case R_MIPS_64:
+               return apply_r_mips_64(location, v, rela);
+       case R_MIPS_HIGHER:
+               return apply_r_mips_higher(location, v, rela);
+       case R_MIPS_HIGHEST:
+               return apply_r_mips_highest(location, v, rela);
+       default:
+               pr_err("%s: Unknown relocation type %u\n", me->name, type);
+               return -EINVAL;
+       }
+
+       return 0;
+}
 
 static int __apply_relocate(Elf_Shdr *sechdrs, const char *strtab,
                            unsigned int symindex, unsigned int relsec,
@@ -311,7 +318,6 @@ static int __apply_relocate(Elf_Shdr *sechdrs, const char *strtab,
                Elf_Mips_Rel *rel;
                Elf_Mips_Rela *rela;
        } r;
-       reloc_handler handler;
        Elf_Sym *sym;
        u32 *location, base;
        unsigned int i, type;
@@ -343,17 +349,6 @@ static int __apply_relocate(Elf_Shdr *sechdrs, const char *strtab,
                }
 
                type = ELF_MIPS_R_TYPE(*r.rel);
-               if (type < ARRAY_SIZE(reloc_handlers))
-                       handler = reloc_handlers[type];
-               else
-                       handler = NULL;
-
-               if (!handler) {
-                       pr_err("%s: Unknown relocation type %u\n",
-                              me->name, type);
-                       err = -EINVAL;
-                       goto out;
-               }
 
                if (rela) {
                        v = sym->st_value + r.rela->r_addend;
@@ -365,7 +360,7 @@ static int __apply_relocate(Elf_Shdr *sechdrs, const char *strtab,
                        r.rel = &r.rel[1];
                }
 
-               err = handler(me, location, base, v, rela);
+               err = reloc_handler(type, me, location, base, v, rela);
                if (err)
                        goto out;
        }