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    Subject[PATCH V2 5/9] objtool: Add support for intra-function calls
    Date
    Change objtool to support intra-function calls. On x86, an intra-function
    call is represented in objtool as a push onto the stack (of the return
    address), and a jump to the destination address. That way the stack
    information is correctly updated and the call flow is still accurate.

    Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
    ---
    include/linux/frame.h | 11 +++
    .../Documentation/stack-validation.txt | 8 ++
    tools/objtool/arch.h | 2 +
    tools/objtool/arch/x86/decode.c | 12 +++
    tools/objtool/check.c | 97 ++++++++++++++++---
    tools/objtool/check.h | 1 +
    6 files changed, 117 insertions(+), 14 deletions(-)

    diff --git a/include/linux/frame.h b/include/linux/frame.h
    index 02d3ca2d9598..c7178e6c9d48 100644
    --- a/include/linux/frame.h
    +++ b/include/linux/frame.h
    @@ -15,9 +15,20 @@
    static void __used __section(.discard.func_stack_frame_non_standard) \
    *__func_stack_frame_non_standard_##func = func

    +/*
    + * This macro indicates that the following intra-function call is valid.
    + * Any non-annotated intra-function call will cause objtool to issue warning.
    + */
    +#define ANNOTATE_INTRA_FUNCTION_CALL \
    + 999: \
    + .pushsection .discard.intra_function_call; \
    + .long 999b; \
    + .popsection;
    +
    #else /* !CONFIG_STACK_VALIDATION */

    #define STACK_FRAME_NON_STANDARD(func)
    +#define ANNOTATE_INTRA_FUNCTION_CALL

    #endif /* CONFIG_STACK_VALIDATION */

    diff --git a/tools/objtool/Documentation/stack-validation.txt b/tools/objtool/Documentation/stack-validation.txt
    index de094670050b..09f863fd32d2 100644
    --- a/tools/objtool/Documentation/stack-validation.txt
    +++ b/tools/objtool/Documentation/stack-validation.txt
    @@ -290,6 +290,14 @@ they mean, and suggestions for how to fix them.
    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646


    +9. file.o: warning: unsupported intra-function call
    +
    + This warning means that a direct call is done to a destination which
    + is not at the beginning of a function. If this is a legit call, you
    + can remove this warning by putting the ANNOTATE_INTRA_FUNCTION_CALL
    + directive right before the call.
    +
    +
    If the error doesn't seem to make sense, it could be a bug in objtool.
    Feel free to ask the objtool maintainer for help.

    diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h
    index ced3765c4f44..4d42c12d9957 100644
    --- a/tools/objtool/arch.h
    +++ b/tools/objtool/arch.h
    @@ -75,4 +75,6 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,

    bool arch_callee_saved_reg(unsigned char reg);

    +void arch_configure_intra_function_call(struct stack_op *op);
    +
    #endif /* _ARCH_H */
    diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
    index a62e032863a8..7ee1561bf7ad 100644
    --- a/tools/objtool/arch/x86/decode.c
    +++ b/tools/objtool/arch/x86/decode.c
    @@ -497,3 +497,15 @@ void arch_initial_func_cfi_state(struct cfi_state *state)
    state->regs[16].base = CFI_CFA;
    state->regs[16].offset = -8;
    }
    +
    +
    +void arch_configure_intra_function_call(struct stack_op *op)
    +{
    + /*
    + * For the impact on the stack, make an intra-function
    + * call behaves like a push of an immediate value (the
    + * return address).
    + */
    + op->src.type = OP_SRC_CONST;
    + op->dest.type = OP_DEST_PUSH;
    +}
    diff --git a/tools/objtool/check.c b/tools/objtool/check.c
    index ab06e9bdd396..bf1e4e94d686 100644
    --- a/tools/objtool/check.c
    +++ b/tools/objtool/check.c
    @@ -644,34 +644,50 @@ static int add_jump_destinations(struct objtool_file *file)
    return 0;
    }

    +static int configure_call(struct objtool_file *file, struct instruction *insn)
    +{
    + unsigned long dest_off;
    +
    + dest_off = insn->offset + insn->len + insn->immediate;
    + insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
    + if (insn->call_dest) {
    + /* regular call */
    + return 0;
    + }
    +
    + /* intra-function call */
    + if (!insn->intra_function_call)
    + WARN_FUNC("intra-function call", insn->sec, insn->offset);
    +
    + dest_off = insn->offset + insn->len + insn->immediate;
    + insn->jump_dest = find_insn(file, insn->sec, dest_off);
    + if (!insn->jump_dest) {
    + WARN_FUNC("can't find call dest at %s+0x%lx",
    + insn->sec, insn->offset,
    + insn->sec->name, dest_off);
    + return -1;
    + }
    +
    + return 0;
    +}
    +
    /*
    * Find the destination instructions for all calls.
    */
    static int add_call_destinations(struct objtool_file *file)
    {
    struct instruction *insn;
    - unsigned long dest_off;
    struct rela *rela;

    for_each_insn(file, insn) {
    - if (insn->type != INSN_CALL)
    + if (insn->type != INSN_CALL || insn->ignore)
    continue;

    rela = find_rela_by_dest_range(insn->sec, insn->offset,
    insn->len);
    if (!rela) {
    - dest_off = insn->offset + insn->len + insn->immediate;
    - insn->call_dest = find_symbol_by_offset(insn->sec,
    - dest_off);
    -
    - if (!insn->call_dest && !insn->ignore) {
    - WARN_FUNC("unsupported intra-function call",
    - insn->sec, insn->offset);
    - if (retpoline)
    - WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
    + if (configure_call(file, insn))
    return -1;
    - }
    -
    } else if (rela->sym->type == STT_SECTION) {
    insn->call_dest = find_symbol_by_offset(rela->sym->sec,
    rela->addend+4);
    @@ -1293,6 +1309,43 @@ static int read_retpoline_hints(struct objtool_file *file)
    return 0;
    }

    +static int read_intra_function_call(struct objtool_file *file)
    +{
    + struct section *sec;
    + struct instruction *insn;
    + struct rela *rela;
    +
    + sec = find_section_by_name(file->elf,
    + ".rela.discard.intra_function_call");
    + if (!sec)
    + return 0;
    +
    + list_for_each_entry(rela, &sec->rela_list, list) {
    + if (rela->sym->type != STT_SECTION) {
    + WARN("unexpected relocation symbol type in %s",
    + sec->name);
    + return -1;
    + }
    +
    + insn = find_insn(file, rela->sym->sec, rela->addend);
    + if (!insn) {
    + WARN("bad .discard.intra_function_call entry");
    + return -1;
    + }
    +
    + if (insn->type != INSN_CALL) {
    + WARN_FUNC("intra_function_call not a direct call",
    + insn->sec, insn->offset);
    + return -1;
    + }
    +
    + arch_configure_intra_function_call(&insn->stack_op);
    + insn->intra_function_call = true;
    + }
    +
    + return 0;
    +}
    +
    static void mark_rodata(struct objtool_file *file)
    {
    struct section *sec;
    @@ -1348,6 +1401,10 @@ static int decode_sections(struct objtool_file *file)
    if (ret)
    return ret;

    + ret = read_intra_function_call(file);
    + if (ret)
    + return ret;
    +
    ret = add_call_destinations(file);
    if (ret)
    return ret;
    @@ -2110,7 +2167,8 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
    return ret;

    if (!no_fp && func && !is_fentry_call(insn) &&
    - !has_valid_stack_frame(&state)) {
    + !has_valid_stack_frame(&state) &&
    + !insn->intra_function_call) {
    WARN_FUNC("call without frame pointer save/setup",
    sec, insn->offset);
    return 1;
    @@ -2119,6 +2177,17 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
    if (dead_end_function(file, insn->call_dest))
    return 0;

    + if (insn->intra_function_call) {
    + update_insn_state(insn, &state);
    + ret = validate_branch(file, func, insn,
    + insn->jump_dest, state);
    + if (ret) {
    + if (backtrace)
    + BT_FUNC("(intra-call)", insn);
    + return ret;
    + }
    + }
    +
    break;

    case INSN_JUMP_CONDITIONAL:
    diff --git a/tools/objtool/check.h b/tools/objtool/check.h
    index 7a91497fee7e..7c7ec3d8fb00 100644
    --- a/tools/objtool/check.h
    +++ b/tools/objtool/check.h
    @@ -36,6 +36,7 @@ struct instruction {
    unsigned int alt_group;
    bool dead_end, ignore, ignore_alts;
    bool hint, save, restore;
    + bool intra_function_call;
    bool retpoline_safe;
    u8 visited;
    u8 ret_offset;
    --
    2.18.2
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