LoongArch: Support R_LARCH_GOT_PC_{LO12,HI20} in modules

GCC >= 13 and GNU assembler >= 2.40 use these relocations to address
external symbols, so we need to add them.

Let the module loader emit GOT entries for data symbols so we would be
able to handle GOT relocations. The GOT entry is just the data's symbol
address.

In module.lds, emit a stub .got section for a section header entry. The
actual content of the section entry will be filled at runtime by module_
frob_arch_sections().

Tested-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

1 files changed, 49 insertions, 5 deletions

diff --git a/arch/loongarch/kernel/module-sections.c b/arch/loongarch/kernel/module-sections.c
index e25c2ccf2665..d296a70b758f 100644
--- a/arch/loongarch/kernel/module-sections.c
+++ b/arch/loongarch/kernel/module-sections.c
@@ -7,7 +7,33 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 
-Elf_Addr module_emit_plt_entry(struct module *mod, unsigned long val)
+Elf_Addr module_emit_got_entry(struct module *mod, Elf_Addr val)
+{
+	struct mod_section *got_sec = &mod->arch.got;
+	int i = got_sec->num_entries;
+	struct got_entry *got = get_got_entry(val, got_sec);
+
+	if (got)
+		return (Elf_Addr)got;
+
+	/* There is no GOT entry for val yet, create a new one. */
+	got = (struct got_entry *)got_sec->shdr->sh_addr;
+	got[i] = emit_got_entry(val);
+
+	got_sec->num_entries++;
+	if (got_sec->num_entries > got_sec->max_entries) {
+		/*
+		 * This may happen when the module contains a GOT_HI20 without
+		 * a paired GOT_LO12. Such a module is broken, reject it.
+		 */
+		pr_err("%s: module contains bad GOT relocation\n", mod->name);
+		return 0;
+	}
+
+	return (Elf_Addr)&got[i];
+}
+
+Elf_Addr module_emit_plt_entry(struct module *mod, Elf_Addr val)
 {
 	int nr;
 	struct mod_section *plt_sec = &mod->arch.plt;
@@ -50,7 +76,8 @@ static bool duplicate_rela(const Elf_Rela *rela, int idx)
 	return false;
 }
 
-static void count_max_entries(Elf_Rela *relas, int num, unsigned int *plts)
+static void count_max_entries(Elf_Rela *relas, int num,
+			      unsigned int *plts, unsigned int *gots)
 {
 	unsigned int i, type;
 
@@ -62,6 +89,10 @@ static void count_max_entries(Elf_Rela *relas, int num, unsigned int *plts)
 			if (!duplicate_rela(relas, i))
 				(*plts)++;
 			break;
+		case R_LARCH_GOT_PC_HI20:
+			if (!duplicate_rela(relas, i))
+				(*gots)++;
+			break;
 		default:
 			break; /* Do nothing. */
 		}
@@ -71,18 +102,24 @@ static void count_max_entries(Elf_Rela *relas, int num, unsigned int *plts)
 int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
 			      char *secstrings, struct module *mod)
 {
-	unsigned int i, num_plts = 0;
+	unsigned int i, num_plts = 0, num_gots = 0;
 
 	/*
 	 * Find the empty .plt sections.
 	 */
 	for (i = 0; i < ehdr->e_shnum; i++) {
-		if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt"))
+		if (!strcmp(secstrings + sechdrs[i].sh_name, ".got"))
+			mod->arch.got.shdr = sechdrs + i;
+		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt"))
 			mod->arch.plt.shdr = sechdrs + i;
 		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt.idx"))
 			mod->arch.plt_idx.shdr = sechdrs + i;
 	}
 
+	if (!mod->arch.got.shdr) {
+		pr_err("%s: module GOT section(s) missing\n", mod->name);
+		return -ENOEXEC;
+	}
 	if (!mod->arch.plt.shdr) {
 		pr_err("%s: module PLT section(s) missing\n", mod->name);
 		return -ENOEXEC;
@@ -105,9 +142,16 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
 		if (!(dst_sec->sh_flags & SHF_EXECINSTR))
 			continue;
 
-		count_max_entries(relas, num_rela, &num_plts);
+		count_max_entries(relas, num_rela, &num_plts, &num_gots);
 	}
 
+	mod->arch.got.shdr->sh_type = SHT_NOBITS;
+	mod->arch.got.shdr->sh_flags = SHF_ALLOC;
+	mod->arch.got.shdr->sh_addralign = L1_CACHE_BYTES;
+	mod->arch.got.shdr->sh_size = (num_gots + 1) * sizeof(struct got_entry);
+	mod->arch.got.num_entries = 0;
+	mod->arch.got.max_entries = num_gots;
+
 	mod->arch.plt.shdr->sh_type = SHT_NOBITS;
 	mod->arch.plt.shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
 	mod->arch.plt.shdr->sh_addralign = L1_CACHE_BYTES;