[PATCH 5.10 030/148] objtool: Add elf_create_undef_symbol()

Greg Kroah-Hartman
2022-07-23T10:00:10Z

From: Peter Zijlstra <peterz@infradead.org>

commit 2f2f7e47f0525cbaad5dd9675fd9d8aa8da12046 upstream.

Allow objtool to create undefined symbols; this allows creating
relocations to symbols not currently in the symbol table.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/20210326151300.064743095@infradead.org
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
tools/objtool/elf.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++
tools/objtool/elf.h | 1
2 files changed, 61 insertions(+)

--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -766,6 +766,66 @@ static int elf_add_string(struct elf *el
return len;
}

+struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name)
+{
+ struct section *symtab;
+ struct symbol *sym;
+ Elf_Data *data;
+ Elf_Scn *s;
+
+ sym = malloc(sizeof(*sym));
+ if (!sym) {
+ perror("malloc");
+ return NULL;
+ }
+ memset(sym, 0, sizeof(*sym));
+
+ sym->name = strdup(name);
+
+ sym->sym.st_name = elf_add_string(elf, NULL, sym->name);
+ if (sym->sym.st_name == -1)
+ return NULL;
+
+ sym->sym.st_info = GELF_ST_INFO(STB_GLOBAL, STT_NOTYPE);
+ // st_other 0
+ // st_shndx 0
+ // st_value 0
+ // st_size 0
+
+ symtab = find_section_by_name(elf, ".symtab");
+ if (!symtab) {
+ WARN("can't find .symtab");
+ return NULL;
+ }
+
+ s = elf_getscn(elf->elf, symtab->idx);
+ if (!s) {
+ WARN_ELF("elf_getscn");
+ return NULL;
+ }
+
+ data = elf_newdata(s);
+ if (!data) {
+ WARN_ELF("elf_newdata");
+ return NULL;
+ }
+
+ data->d_buf = &sym->sym;
+ data->d_size = sizeof(sym->sym);
+ data->d_align = 1;
+
+ sym->idx = symtab->len / sizeof(sym->sym);
+
+ symtab->len += data->d_size;
+ symtab->changed = true;
+
+ sym->sec = find_section_by_index(elf, 0);
+
+ elf_add_symbol(elf, sym);
+
+ return sym;
+}
+
struct section *elf_create_section(struct elf *elf, const char *name,
unsigned int sh_flags, size_t entsize, int nr)
{
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -133,6 +133,7 @@ int elf_write_insn(struct elf *elf, stru
unsigned long offset, unsigned int len,
const char *insn);
int elf_write_reloc(struct elf *elf, struct reloc *reloc);
+struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name);
int elf_write(struct elf *elf);
void elf_close(struct elf *elf);