objtool: Use target file class size instead of a compiled constant

In order to allow using objtool on cross-built kernels,
determine size of long from elf data instead of using
sizeof(long) at build time.

For the time being this covers only mcount.

[Sathvika Vasireddy: Rename variable "size" to "addrsize" and function
"elf_class_size()" to "elf_class_addrsize()", and modify
create_mcount_loc_sections() function to follow reverse christmas tree
format to order local variable declarations.]

Tested-by: Naveen N. Rao <[email protected]>
Reviewed-by: Naveen N. Rao <[email protected]>
Acked-by: Josh Poimboeuf <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Christophe Leroy <[email protected]>
Signed-off-by: Sathvika Vasireddy <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: chleroy

tools/objtool/check.c

@@ -852,9 +852,9 @@ static int create_ibt_endbr_seal_sections(struct objtool_file *file)
 
 static int create_mcount_loc_sections(struct objtool_file *file)
 {
-	struct section *sec;
-	unsigned long *loc;
+	int addrsize = elf_class_addrsize(file->elf);
 	struct instruction *insn;
+	struct section *sec;
 	int idx;
 
 	sec = find_section_by_name(file->elf, "__mcount_loc");
@@ -871,23 +871,25 @@ static int create_mcount_loc_sections(struct objtool_file *file)
 	list_for_each_entry(insn, &file->mcount_loc_list, call_node)
 		idx++;
 
-	sec = elf_create_section(file->elf, "__mcount_loc", 0, sizeof(unsigned long), idx);
+	sec = elf_create_section(file->elf, "__mcount_loc", 0, addrsize, idx);
 	if (!sec)
 		return -1;
 
+	sec->sh.sh_addralign = addrsize;
+
 	idx = 0;
 	list_for_each_entry(insn, &file->mcount_loc_list, call_node) {
+		void *loc;
 
-		loc = (unsigned long *)sec->data->d_buf + idx;
-		memset(loc, 0, sizeof(unsigned long));
+		loc = sec->data->d_buf + idx;
+		memset(loc, 0, addrsize);
 
-		if (elf_add_reloc_to_insn(file->elf, sec,
-					  idx * sizeof(unsigned long),
+		if (elf_add_reloc_to_insn(file->elf, sec, idx,
 					  R_X86_64_64,
 					  insn->sec, insn->offset))
 			return -1;
 
-		idx++;
+		idx += addrsize;
 	}
 
 	return 0;

tools/objtool/elf.c

@@ -1129,6 +1129,7 @@ static struct section *elf_create_rela_reloc_section(struct elf *elf, struct sec
 {
 	char *relocname;
 	struct section *sec;
+	int addrsize = elf_class_addrsize(elf);
 
 	relocname = malloc(strlen(base->name) + strlen(".rela") + 1);
 	if (!relocname) {
@@ -1138,7 +1139,10 @@ static struct section *elf_create_rela_reloc_section(struct elf *elf, struct sec
 	strcpy(relocname, ".rela");
 	strcat(relocname, base->name);
 
-	sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0);
+	if (addrsize == sizeof(u32))
+		sec = elf_create_section(elf, relocname, 0, sizeof(Elf32_Rela), 0);
+	else
+		sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0);
 	free(relocname);
 	if (!sec)
 		return NULL;
@@ -1147,7 +1151,7 @@ static struct section *elf_create_rela_reloc_section(struct elf *elf, struct sec
 	sec->base = base;
 
 	sec->sh.sh_type = SHT_RELA;
-	sec->sh.sh_addralign = 8;
+	sec->sh.sh_addralign = addrsize;
 	sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
 	sec->sh.sh_info = base->idx;
 	sec->sh.sh_flags = SHF_INFO_LINK;

tools/objtool/include/objtool/elf.h

@@ -142,6 +142,14 @@ static inline bool has_multiple_files(struct elf *elf)
 	return elf->num_files > 1;
 }
 
+static inline int elf_class_addrsize(struct elf *elf)
+{
+	if (elf->ehdr.e_ident[EI_CLASS] == ELFCLASS32)
+		return sizeof(u32);
+	else
+		return sizeof(u64);
+}
+
 struct elf *elf_open_read(const char *name, int flags);
 struct section *elf_create_section(struct elf *elf, const char *name, unsigned int sh_flags, size_t entsize, int nr);