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Subject[PATCH mips-next 1/2] 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>
---
arch/mips/kernel/module.c | 109 ++++++++++++++++++--------------------
1 file changed, 52 insertions(+), 57 deletions(-)

diff --git a/arch/mips/kernel/module.c b/arch/mips/kernel/module.c
index 3c0c3d1260c1..14f46d17500a 100644
--- 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;
}
--
2.30.0

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