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    Subject[PATCH 5.10 007/130] objtool: Assume only ELF functions do sibling calls
    Date
    From: Josh Poimboeuf <jpoimboe@redhat.com>

    commit ecf11ba4d066fe527586c6edd6ca68457ca55cf4 upstream.

    There's an inconsistency in how sibling calls are detected in
    non-function asm code, depending on the scope of the object. If the
    target code is external to the object, objtool considers it a sibling
    call. If the target code is internal but not a function, objtool
    *doesn't* consider it a sibling call.

    This can cause some inconsistencies between per-object and vmlinux.o
    validation.

    Instead, assume only ELF functions can do sibling calls. This generally
    matches existing reality, and makes sibling call validation consistent
    between vmlinux.o and per-object.

    Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Link: https://lore.kernel.org/r/0e9ab6f3628cc7bf3bde7aa6762d54d7df19ad78.1611263461.git.jpoimboe@redhat.com
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    tools/objtool/check.c | 36 ++++++++++++++++++++++--------------
    1 file changed, 22 insertions(+), 14 deletions(-)

    --- a/tools/objtool/check.c
    +++ b/tools/objtool/check.c
    @@ -109,15 +109,20 @@ static struct instruction *prev_insn_sam

    static bool is_sibling_call(struct instruction *insn)
    {
    + /*
    + * Assume only ELF functions can make sibling calls. This ensures
    + * sibling call detection consistency between vmlinux.o and individual
    + * objects.
    + */
    + if (!insn->func)
    + return false;
    +
    /* An indirect jump is either a sibling call or a jump to a table. */
    if (insn->type == INSN_JUMP_DYNAMIC)
    return list_empty(&insn->alts);

    - if (!is_static_jump(insn))
    - return false;
    -
    /* add_jump_destinations() sets insn->call_dest for sibling calls. */
    - return !!insn->call_dest;
    + return (is_static_jump(insn) && insn->call_dest);
    }

    /*
    @@ -788,7 +793,7 @@ static int add_jump_destinations(struct
    continue;

    reloc = find_reloc_by_dest_range(file->elf, insn->sec,
    - insn->offset, insn->len);
    + insn->offset, insn->len);
    if (!reloc) {
    dest_sec = insn->sec;
    dest_off = arch_jump_destination(insn);
    @@ -808,18 +813,21 @@ static int add_jump_destinations(struct

    insn->retpoline_safe = true;
    continue;
    - } else if (reloc->sym->sec->idx) {
    - dest_sec = reloc->sym->sec;
    - dest_off = reloc->sym->sym.st_value +
    - arch_dest_reloc_offset(reloc->addend);
    - } else {
    - /* external sibling call */
    + } else if (insn->func) {
    + /* internal or external sibling call (with reloc) */
    insn->call_dest = reloc->sym;
    if (insn->call_dest->static_call_tramp) {
    list_add_tail(&insn->static_call_node,
    &file->static_call_list);
    }
    continue;
    + } else if (reloc->sym->sec->idx) {
    + dest_sec = reloc->sym->sec;
    + dest_off = reloc->sym->sym.st_value +
    + arch_dest_reloc_offset(reloc->addend);
    + } else {
    + /* non-func asm code jumping to another file */
    + continue;
    }

    insn->jump_dest = find_insn(file, dest_sec, dest_off);
    @@ -868,7 +876,7 @@ static int add_jump_destinations(struct
    } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
    insn->jump_dest->offset == insn->jump_dest->func->offset) {

    - /* internal sibling call */
    + /* internal sibling call (without reloc) */
    insn->call_dest = insn->jump_dest->func;
    if (insn->call_dest->static_call_tramp) {
    list_add_tail(&insn->static_call_node,
    @@ -2570,7 +2578,7 @@ static int validate_branch(struct objtoo

    case INSN_JUMP_CONDITIONAL:
    case INSN_JUMP_UNCONDITIONAL:
    - if (func && is_sibling_call(insn)) {
    + if (is_sibling_call(insn)) {
    ret = validate_sibling_call(insn, &state);
    if (ret)
    return ret;
    @@ -2592,7 +2600,7 @@ static int validate_branch(struct objtoo

    case INSN_JUMP_DYNAMIC:
    case INSN_JUMP_DYNAMIC_CONDITIONAL:
    - if (func && is_sibling_call(insn)) {
    + if (is_sibling_call(insn)) {
    ret = validate_sibling_call(insn, &state);
    if (ret)
    return ret;

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