Re: objtool "no non-local symbols" error with tip of tree LLVM

Peter Zijlstra
2022-05-17T15:44:00Z

On Tue, May 17, 2022 at 05:33:59PM +0200, Peter Zijlstra wrote:
> On Mon, May 16, 2022 at 11:40:06PM +0200, Peter Zijlstra wrote:
> > Does something simple like this work? If not, I'll try and reproduce
> > tomorrow, it shouldn't be too hard to fix.
>
> Oh, man, I so shouldn't have said that :/
>
> I have something that almost works, except it now mightly upsets
> modpost.
>
> I'm not entirely sure how the old code worked as well as it did. Oh
> well, I'll get it sorted.

Pff, it's been a *long* day.. here this works.

---
tools/objtool/elf.c | 191 ++++++++++++++++++++++++++++++++++------------------
1 file changed, 125 insertions(+), 66 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index ebf2ba5755c1..a9c3e27527de 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -600,24 +600,24 @@ static void elf_dirty_reloc_sym(struct elf *elf, struct symbol *sym)
}

/*
- * Move the first global symbol, as per sh_info, into a new, higher symbol
- * index. This fees up the shndx for a new local symbol.
+ * The libelf API is terrible; gelf_update_sym*() takes a data block relative
+ * index value. As such, iterate the data blocks and adjust index until it fits.
+ *
+ * If no data block is found, allow adding a new data block provided the index
+ * is only one past the end.
*/
-static int elf_move_global_symbol(struct elf *elf, struct section *symtab,
- struct section *symtab_shndx)
+static int elf_update_symbol(struct elf *elf, struct section *symtab,
+ struct section *symtab_shndx, struct symbol *sym)
{
- Elf_Data *data, *shndx_data = NULL;
- Elf32_Word first_non_local;
- struct symbol *sym;
- Elf_Scn *s;
+ Elf_Data *symtab_data = NULL, *shndx_data = NULL;
+ Elf32_Word shndx = sym->sec->idx;
+ Elf_Scn *s, *t = NULL;
+ int size, idx = sym->idx;

- first_non_local = symtab->sh.sh_info;
-
- sym = find_symbol_by_index(elf, first_non_local);
- if (!sym) {
- WARN("no non-local symbols !?");
- return first_non_local;
- }
+ if (elf->ehdr.e_ident[EI_CLASS] == ELFCLASS32)
+ size = sizeof(Elf32_Sym);
+ else
+ size = sizeof(Elf64_Sym);

s = elf_getscn(elf->elf, symtab->idx);
if (!s) {
@@ -625,79 +625,120 @@ static int elf_move_global_symbol(struct elf *elf, struct section *symtab,
return -1;
}

- data = elf_newdata(s);
- if (!data) {
- WARN_ELF("elf_newdata");
- return -1;
+ if (symtab_shndx) {
+ t = elf_getscn(elf->elf, symtab_shndx->idx);
+ if (!t) {
+ WARN_ELF("elf_getscn");
+ return -1;
+ }
}

- data->d_buf = &sym->sym;
- data->d_size = sizeof(sym->sym);
- data->d_align = 1;
- data->d_type = ELF_T_SYM;
+ for (;;) {
+ symtab_data = elf_getdata(s, symtab_data);
+ if (t)
+ shndx_data = elf_getdata(t, shndx_data);

- sym->idx = symtab->sh.sh_size / sizeof(sym->sym);
- elf_dirty_reloc_sym(elf, sym);
+ if (!symtab_data) {
+ if (!idx) {
+ void *buf;

- symtab->sh.sh_info += 1;
- symtab->sh.sh_size += data->d_size;
- symtab->changed = true;
+ symtab_data = elf_newdata(s);
+ if (t)
+ shndx_data = elf_newdata(t);

- if (symtab_shndx) {
- s = elf_getscn(elf->elf, symtab_shndx->idx);
- if (!s) {
- WARN_ELF("elf_getscn");
+ buf = calloc(1, size);
+ if (!buf) {
+ WARN("malloc");
+ return -1;
+ }
+
+ symtab_data->d_buf = buf;
+ symtab_data->d_size = size;
+ symtab_data->d_align = 1;
+ symtab_data->d_type = ELF_T_SYM;
+
+ symtab->sh.sh_size += size;
+ symtab->changed = true;
+
+ if (t) {
+ shndx_data->d_buf = &sym->sec->idx;
+ shndx_data->d_size = sizeof(Elf32_Word);
+ shndx_data->d_align = 4;
+ shndx_data->d_type = ELF_T_WORD;
+
+ symtab_shndx->sh.sh_size += 4;
+ symtab_shndx->changed = true;
+ }
+
+ break;
+ }
+
+ WARN("index out of range");
return -1;
}

- shndx_data = elf_newdata(s);
- if (!shndx_data) {
- WARN_ELF("elf_newshndx_data");
+ if (!symtab_data->d_size) {
+ WARN("zero size data");
return -1;
}

- shndx_data->d_buf = &sym->sec->idx;
- shndx_data->d_size = sizeof(Elf32_Word);
- shndx_data->d_align = 4;
- shndx_data->d_type = ELF_T_WORD;
+ if (idx * size < symtab_data->d_size)
+ break;

- symtab_shndx->sh.sh_size += 4;
- symtab_shndx->changed = true;
+ idx -= symtab_data->d_size / size;
}

- return first_non_local;
+ if (idx < 0) {
+ WARN("negative index");
+ return -1;
+ }
+
+ if (shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) {
+ sym->sym.st_shndx = shndx;
+ if (!shndx_data)
+ shndx = 0;
+ } else {
+ sym->sym.st_shndx = SHN_XINDEX;
+ if (!shndx_data) {
+ WARN("no .symtab_shndx");
+ return -1;
+ }
+ }
+
+ if (!gelf_update_symshndx(symtab_data, shndx_data, idx, &sym->sym, shndx)) {
+ WARN_ELF("gelf_update_symshndx");
+ return -1;
+ }
+
+ return 0;
}

static struct symbol *
elf_create_section_symbol(struct elf *elf, struct section *sec)
{
struct section *symtab, *symtab_shndx;
- Elf_Data *shndx_data = NULL;
- struct symbol *sym;
- Elf32_Word shndx;
+ Elf32_Word first_non_local, new;
+ struct symbol *sym, *old;
+ int size;
+
+ if (elf->ehdr.e_ident[EI_CLASS] == ELFCLASS32)
+ size = sizeof(Elf32_Sym);
+ else
+ size = sizeof(Elf64_Sym);

symtab = find_section_by_name(elf, ".symtab");
if (symtab) {
symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
- if (symtab_shndx)
- shndx_data = symtab_shndx->data;
} else {
WARN("no .symtab");
return NULL;
}

- sym = malloc(sizeof(*sym));
+ sym = calloc(1, sizeof(*sym));
if (!sym) {
perror("malloc");
return NULL;
}
- memset(sym, 0, sizeof(*sym));
-
- sym->idx = elf_move_global_symbol(elf, symtab, symtab_shndx);
- if (sym->idx < 0) {
- WARN("elf_move_global_symbol");
- return NULL;
- }

sym->name = sec->name;
sym->sec = sec;
@@ -707,24 +748,42 @@ elf_create_section_symbol(struct elf *elf, struct section *sec)
// st_other 0
// st_value 0
// st_size 0
- shndx = sec->idx;
- if (shndx >= SHN_UNDEF && shndx < SHN_LORESERVE) {
- sym->sym.st_shndx = shndx;
- if (!shndx_data)
- shndx = 0;
- } else {
- sym->sym.st_shndx = SHN_XINDEX;
- if (!shndx_data) {
- WARN("no .symtab_shndx");
+
+ new = symtab->sh.sh_size / size;
+
+ /*
+ * Move the first global symbol, as per sh_info, into a new, higher
+ * symbol index. This fees up a spot for a new local symbol.
+ */
+ first_non_local = symtab->sh.sh_info;
+ old = find_symbol_by_index(elf, first_non_local);
+ if (old) {
+ old->idx = new;
+
+ hlist_del(&old->hash);
+ elf_hash_add(symbol, &old->hash, old->idx);
+
+ elf_dirty_reloc_sym(elf, old);
+
+ if (elf_update_symbol(elf, symtab, symtab_shndx, old)) {
+ WARN("elf_update_symbol move");
return NULL;
}
+
+ new = first_non_local;
}

- if (!gelf_update_symshndx(symtab->data, shndx_data, sym->idx, &sym->sym, shndx)) {
- WARN_ELF("gelf_update_symshndx");
+ sym->idx = new;
+ if (elf_update_symbol(elf, symtab, symtab_shndx, sym)) {
+ WARN("elf_update_symbol");
return NULL;
}

+ /*
+ * Either way, we added a LOCAL symbol.
+ */
+ symtab->sh.sh_info += 1;
+
elf_add_symbol(elf, sym);

return sym;