[PATCH] riscv: optimize ELF relocation function in riscv

[Amma.Lee]

The patch can optimize the running times of "insmod" command by modify ELF
relocation function.
In the riscv kernel, when install the ELF driver which contains multiple
symbol table items to be relocated, kernel takes a lot of time to
execute the relocation. For example, we install a 3+MB driver need 180+s.

We focus on the riscv kernel handle R_RISCV_HI20 and R_RISCV_LO12 type
items relocation function and find that there are two for-loops in this
function. If we modify the begin number in the second for-loops iteration,
we could save significant time for installation. We install the 3+MB
driver could just need 2s.

Signed-off-by: Amma.Lee<lixiaoyun at binary-semi.com>
---
 arch/riscv/kernel/module.c | 69 ++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 61 insertions(+), 8 deletions(-)

diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
index 7c651d5..55507b0 100755
--- a/arch/riscv/kernel/module.c
+++ b/arch/riscv/kernel/module.c
@@ -345,13 +345,13 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
 	int (*handler)(struct module *me, u32 *location, Elf_Addr v);
 	Elf_Sym *sym;
 	u32 *location;
-	unsigned int i, type;
+	unsigned int i, type, j_idx;
 	Elf_Addr v;
 	int res;
 
 	pr_debug("Applying relocate section %u to %u\n", relsec,
 	       sechdrs[relsec].sh_info);
-
+	j_idx = 0;
 	for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
 		/* This is where to make the change */
 		location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
@@ -385,8 +385,9 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
 
 		if (type == R_RISCV_PCREL_LO12_I || type == R_RISCV_PCREL_LO12_S) {
 			unsigned int j;
-
-			for (j = 0; j < sechdrs[relsec].sh_size / sizeof(*rel); j++) {
+			/*Modify the j for-loops begin number from last iterates end value*/
+			for (j = j_idx; j < sechdrs[relsec].sh_size / sizeof(*rel); j++) {
+			/* Modify end */
 				unsigned long hi20_loc =
 					sechdrs[sechdrs[relsec].sh_info].sh_addr
 					+ rel[j].r_offset;
@@ -420,11 +421,63 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
 				}
 			}
 			if (j == sechdrs[relsec].sh_size / sizeof(*rel)) {
-				pr_err(
-				  "%s: Can not find HI20 relocation information\n",
-				  me->name);
-				return -EINVAL;
+				if (j_idx == 0) {
+					pr_err(
+						"%s: Can not find HI20 relocation information\n",
+						me->name);
+					return -EINVAL;
+				}
+
+
+				for (j = 0; j < j_idx; j++) {
+					unsigned long hi20_loc =
+						sechdrs[sechdrs[relsec].sh_info].sh_addr
+						+ rel[j].r_offset;
+					u32 hi20_type = ELF_RISCV_R_TYPE(rel[j].r_info);
+
+
+					/* Find the corresponding HI20 relocation entry */
+					if (hi20_loc == sym->st_value
+						&& (hi20_type == R_RISCV_PCREL_HI20
+						|| hi20_type == R_RISCV_GOT_HI20)) {
+						s32 hi20, lo12;
+						Elf_Sym *hi20_sym =
+							(Elf_Sym *)sechdrs[symindex].sh_addr
+							+ ELF_RISCV_R_SYM(rel[j].r_info);
+						unsigned long hi20_sym_val =
+							hi20_sym->st_value
+							+ rel[j].r_addend;
+
+
+						/* Calculate lo12 */
+						size_t offset = hi20_sym_val - hi20_loc;
+						/* Calculate lo12 */
+						if (IS_ENABLED(CONFIG_MODULE_SECTIONS)
+							&& hi20_type == R_RISCV_GOT_HI20) {
+							offset = module_emit_got_entry(
+								me, hi20_sym_val);
+							offset = offset - hi20_loc;
+
+						}
+						hi20 = (offset + 0x800) & 0xfffff000;
+						lo12 = offset - hi20;
+						v = lo12;
+
+						break;
+					}
+				}
+
+				if (j == j_idx) {
+					pr_err(
+						"%s: Can not find HI20 relocation information\n",
+						me->name);
+					return -EINVAL;
+				}
+
+
 			}
+
+			j_idx = j;
 		}
 
 		res = handler(me, location, v);
-- 
1.9.1