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Subject[PATCH mips-next 2/2] 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>
---
arch/mips/kernel/relocate.c | 54 ++++++++++++++++++++-----------------
1 file changed, 30 insertions(+), 24 deletions(-)

diff --git a/arch/mips/kernel/relocate.c b/arch/mips/kernel/relocate.c
index 47aeb3350a76..c643c816cbe0 100644
--- a/arch/mips/kernel/relocate.c
+++ b/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)
@@ -114,7 +110,8 @@ 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 */
@@ -122,17 +119,33 @@ static int __init apply_r_mips_hi16_rel(u32 *loc_orig, u32 *loc_new, long offset
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;

--
2.30.0

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