Re: [PATCH] objtool: Check local label in is_sibling_call() and add_jump_destinations()

[Huacai Chen]

Looks good to me.

Reviewed-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>

On Tue, Aug 15, 2023 at 4:36 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
>
> When update the latest upstream gcc and binutils which enables linker
> relaxation by default, it generates more objtool warnings on LoongArch,
> like this:
>
>   init/version.o: warning: objtool: early_hostname+0x20: sibling call from callable instruction with modified stack frame
>
> We can see that the branch and jump operation about local label ".L2"
> is not sibling call, because a sibling call is a tail-call to another
> symbol. In this case, make is_sibling_call() return false, set dest_sec
> and dest_off to calculate jump_dest in add_jump_destinations().
>
> Here are some detailed info:
> [fedora@linux 6.5.test]$ gcc --version
> gcc (GCC) 14.0.0 20230803 (experimental)
> [fedora@linux 6.5.test]$ as --version
> GNU assembler (GNU Binutils) 2.41.50.20230803
> [fedora@linux 6.5.test]$ objdump -M no-aliases -D init/version.o
> 0000000000000000 <early_hostname>:
>    0:   00150085        or              $a1, $a0, $zero
>    4:   1a000004        pcalau12i       $a0, 0
>    8:   02ffc063        addi.d          $sp, $sp, -16
>    c:   02810406        addi.w          $a2, $zero, 65
>   10:   02c00084        addi.d          $a0, $a0, 0
>   14:   29c02061        st.d            $ra, $sp, 8
>   18:   54000000        bl              0       # 18 <early_hostname+0x18>
>   1c:   0281000c        addi.w          $t0, $zero, 64
>   20:   6c001584        bgeu            $t0, $a0, 20    # 34 <.L2>
>   24:   1a000004        pcalau12i       $a0, 0
>   28:   02810005        addi.w          $a1, $zero, 64
>   2c:   02c00084        addi.d          $a0, $a0, 0
>   30:   54000000        bl              0       # 30 <early_hostname+0x30>
>
> 0000000000000034 <.L2>:
>   34:   28c02061        ld.d            $ra, $sp, 8
>   38:   00150004        or              $a0, $zero, $zero
>   3c:   02c04063        addi.d          $sp, $sp, 16
>   40:   4c000020        jirl            $zero, $ra, 0
>
> By the way, it need to move insn_reloc() before is_sibling_call()
> to avoid implicit declaration build error.
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> ---
>  tools/objtool/check.c | 69 ++++++++++++++++++++++++++++++---------------------
>  1 file changed, 41 insertions(+), 28 deletions(-)
>
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index 8936a05..fea3675 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -161,12 +161,39 @@ static bool is_jump_table_jump(struct instruction *insn)
>                insn_jump_table(alt_group->orig_group->first_insn);
>  }
>
> -static bool is_sibling_call(struct instruction *insn)
> +static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
> +{
> +       struct reloc *reloc;
> +
> +       if (insn->no_reloc)
> +               return NULL;
> +
> +       if (!file)
> +               return NULL;
> +
> +       reloc = find_reloc_by_dest_range(file->elf, insn->sec,
> +                                        insn->offset, insn->len);
> +       if (!reloc) {
> +               insn->no_reloc = 1;
> +               return NULL;
> +       }
> +
> +       return reloc;
> +}
> +
> +static bool is_sibling_call(struct objtool_file *file, struct instruction *insn)
>  {
>         /*
>          * Assume only STT_FUNC calls have jump-tables.
>          */
>         if (insn_func(insn)) {
> +               struct reloc *reloc = insn_reloc(file, insn);
> +
> +               /* Disallow sibling calls into STT_NOTYPE if it is local lable */
> +               if (reloc && reloc->sym->type == STT_NOTYPE &&
> +                   strncmp(reloc->sym->name, ".L", 2) == 0)
> +                       return false;
> +
>                 /* An indirect jump is either a sibling call or a jump to a table. */
>                 if (insn->type == INSN_JUMP_DYNAMIC)
>                         return !is_jump_table_jump(insn);
> @@ -232,7 +259,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
>          * of the sibling call returns.
>          */
>         func_for_each_insn(file, func, insn) {
> -               if (is_sibling_call(insn)) {
> +               if (is_sibling_call(file, insn)) {
>                         struct instruction *dest = insn->jump_dest;
>
>                         if (!dest)
> @@ -743,7 +770,7 @@ static int create_static_call_sections(struct objtool_file *file)
>                 if (!elf_init_reloc_data_sym(file->elf, sec,
>                                              idx * sizeof(*site) + 4,
>                                              (idx * 2) + 1, key_sym,
> -                                            is_sibling_call(insn) * STATIC_CALL_SITE_TAIL))
> +                                            is_sibling_call(file, insn) * STATIC_CALL_SITE_TAIL))
>                         return -1;
>
>                 idx++;
> @@ -1298,26 +1325,6 @@ __weak bool arch_is_rethunk(struct symbol *sym)
>         return false;
>  }
>
> -static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
> -{
> -       struct reloc *reloc;
> -
> -       if (insn->no_reloc)
> -               return NULL;
> -
> -       if (!file)
> -               return NULL;
> -
> -       reloc = find_reloc_by_dest_range(file->elf, insn->sec,
> -                                        insn->offset, insn->len);
> -       if (!reloc) {
> -               insn->no_reloc = 1;
> -               return NULL;
> -       }
> -
> -       return reloc;
> -}
> -
>  static void remove_insn_ops(struct instruction *insn)
>  {
>         struct stack_op *op, *next;
> @@ -1560,8 +1567,14 @@ static int add_jump_destinations(struct objtool_file *file)
>                          * External sibling call or internal sibling call with
>                          * STT_FUNC reloc.
>                          */
> -                       add_call_dest(file, insn, reloc->sym, true);
> -                       continue;
> +                       if (reloc->sym->type == STT_NOTYPE &&
> +                           strncmp(reloc->sym->name, ".L", 2) == 0) {
> +                               dest_sec = insn->sec;
> +                               dest_off = arch_jump_destination(insn);
> +                       } else {
> +                               add_call_dest(file, insn, reloc->sym, true);
> +                               continue;
> +                       }
>                 } else if (reloc->sym->sec->idx) {
>                         dest_sec = reloc->sym->sec;
>                         dest_off = reloc->sym->sym.st_value +
> @@ -3649,7 +3662,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
>
>                 case INSN_JUMP_CONDITIONAL:
>                 case INSN_JUMP_UNCONDITIONAL:
> -                       if (is_sibling_call(insn)) {
> +                       if (is_sibling_call(file, insn)) {
>                                 ret = validate_sibling_call(file, insn, &state);
>                                 if (ret)
>                                         return ret;
> @@ -3670,7 +3683,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
>
>                 case INSN_JUMP_DYNAMIC:
>                 case INSN_JUMP_DYNAMIC_CONDITIONAL:
> -                       if (is_sibling_call(insn)) {
> +                       if (is_sibling_call(file, insn)) {
>                                 ret = validate_sibling_call(file, insn, &state);
>                                 if (ret)
>                                         return ret;
> @@ -3834,7 +3847,7 @@ static int validate_unret(struct objtool_file *file, struct instruction *insn)
>
>                 case INSN_JUMP_UNCONDITIONAL:
>                 case INSN_JUMP_CONDITIONAL:
> -                       if (!is_sibling_call(insn)) {
> +                       if (!is_sibling_call(file, insn)) {
>                                 if (!insn->jump_dest) {
>                                         WARN_INSN(insn, "unresolved jump target after linking?!?");
>                                         return -1;
> --
> 2.1.0
>
>