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    Subject[PATCH 15/35] objtool: More complex static jump implementation
    When using something like:

    -#define sched_feat(x) (static_branch_##x(&sched_feat_keys[__SCHED_FEAT_##x]))
    +#define sched_feat(x) (static_branch_##x(&sched_feat_keys[__SCHED_FEAT_##x]) && \
    + (arch_static_assert(), true))

    we get an objtool assertion fail like:

    kernel/sched/fair.o: warning: objtool: hrtick_update()+0xd: static assert FAIL

    where:

    0000000000001140 <hrtick_update>:
    1140: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
    1145: c3 retq
    1146: 48 8b b7 30 09 00 00 mov 0x930(%rdi),%rsi
    114d: 8b 87 d8 09 00 00 mov 0x9d8(%rdi),%eax
    1153: 48 0f a3 05 00 00 00 bt %rax,0x0(%rip) # 115b <hrtick_update+0x1b>
    115a: 00
    1157: R_X86_64_PC32 __cpu_active_mask-0x4

    and:

    RELOCATION RECORDS FOR [__jump_table]:
    0000000000000150 R_X86_64_64 .text+0x0000000000001140
    0000000000000158 R_X86_64_64 .text+0x0000000000001146

    RELOCATION RECORDS FOR [.discard.jump_assert]:
    0000000000000028 R_X86_64_64 .text+0x000000000000114d

    IOW, GCC managed to place the assertion 1 instruction _after_ the
    static jump target (it lifted a load over it).

    So while the code generation is fine, the assertion gets placed wrong.
    We can 'fix' this by not only considering the immediate static jump
    locations but also all the unconditional code after it, terminating
    the basic block on any unconditional instruction or branch entry
    point.

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    ---
    tools/objtool/check.c | 41 +++++++++++++++++++++++++++++++++++++++++
    tools/objtool/check.h | 2 +-
    2 files changed, 42 insertions(+), 1 deletion(-)

    --- a/tools/objtool/check.c
    +++ b/tools/objtool/check.c
    @@ -520,6 +520,8 @@ static int add_jump_destinations(struct
    dest_off);
    return -1;
    }
    +
    + insn->jump_dest->branch_target = true;
    }

    return 0;
    @@ -1197,6 +1199,41 @@ static int read_retpoline_hints(struct o
    return 0;
    }

    +static int grow_static_blocks(struct objtool_file *file)
    +{
    + struct instruction *insn;
    + bool static_block = false;
    +
    + for_each_insn(file, insn) {
    + if (!static_block && !insn->static_jump_dest)
    + continue;
    +
    + if (insn->static_jump_dest) {
    + static_block = true;
    + continue;
    + }
    +
    + if (insn->branch_target) {
    + static_block = false;
    + continue;
    + } else switch (insn->type) {
    + case INSN_JUMP_CONDITIONAL:
    + case INSN_JUMP_UNCONDITIONAL:
    + case INSN_JUMP_DYNAMIC:
    + case INSN_CALL:
    + case INSN_CALL_DYNAMIC:
    + case INSN_RETURN:
    + case INSN_BUG:
    + static_block = false;
    + continue;
    + }
    +
    + insn->static_jump_dest = static_block;
    + }
    +
    + return 0;
    +}
    +
    static int decode_sections(struct objtool_file *file)
    {
    int ret;
    @@ -1239,6 +1276,10 @@ static int decode_sections(struct objtoo
    if (ret)
    return ret;

    + ret = grow_static_blocks(file);
    + if (ret)
    + return ret;
    +
    return 0;
    }

    --- a/tools/objtool/check.h
    +++ b/tools/objtool/check.h
    @@ -45,7 +45,7 @@ struct instruction {
    unsigned char type;
    unsigned long immediate;
    bool alt_group, visited, dead_end, ignore, hint, save, restore, ignore_alts;
    - bool static_jump_dest, retpoline_safe;
    + bool static_jump_dest, retpoline_safe, branch_target;
    struct symbol *call_dest;
    struct instruction *jump_dest;
    struct list_head alts;

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