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    Subject[PATCH v3 28/59] objtool: Allow !PC relative relocations
    From: Peter Zijlstra <peterz@infradead.org>

    Objtool doesn't currently much like per-cpu usage in alternatives:

    arch/x86/entry/entry_64.o: warning: objtool: .altinstr_replacement+0xf: unsupported relocation in alternatives section
    f: 65 c7 04 25 00 00 00 00 00 00 00 80 movl $0x80000000,%gs:0x0 13: R_X86_64_32S __x86_call_depth

    Since the R_X86_64_32S relocation is location invariant (it's
    computation doesn't include P - the address of the location itself),
    it can be trivially allowed.

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    ---
    tools/objtool/arch/x86/decode.c | 42 +++++++++++++++++++++++++++++-----
    tools/objtool/check.c | 6 +---
    tools/objtool/include/objtool/arch.h | 6 ++--
    tools/objtool/include/objtool/check.h | 17 +++++++------
    4 files changed, 51 insertions(+), 20 deletions(-)

    --- a/tools/objtool/arch/x86/decode.c
    +++ b/tools/objtool/arch/x86/decode.c
    @@ -73,6 +73,30 @@ unsigned long arch_jump_destination(stru
    return insn->offset + insn->len + insn->immediate;
    }

    +bool arch_pc_relative_reloc(struct reloc *reloc)
    +{
    + /*
    + * All relocation types where P (the address of the target)
    + * is included in the computation.
    + */
    + switch (reloc->type) {
    + case R_X86_64_PC8:
    + case R_X86_64_PC16:
    + case R_X86_64_PC32:
    + case R_X86_64_PC64:
    +
    + case R_X86_64_PLT32:
    + case R_X86_64_GOTPC32:
    + case R_X86_64_GOTPCREL:
    + return true;
    +
    + default:
    + break;
    + }
    +
    + return false;
    +}
    +
    #define ADD_OP(op) \
    if (!(op = calloc(1, sizeof(*op)))) \
    return -1; \
    --- a/tools/objtool/check.c
    +++ b/tools/objtool/check.c
    @@ -1622,7 +1620,7 @@ static int handle_group_alt(struct objto
    * accordingly.
    */
    alt_reloc = insn_reloc(file, insn);
    - if (alt_reloc &&
    + if (alt_reloc && arch_pc_relative_reloc(alt_reloc) &&
    !arch_support_alt_relocation(special_alt, insn, alt_reloc)) {

    WARN_FUNC("unsupported relocation in alternatives section",
    --- a/tools/objtool/include/objtool/arch.h
    +++ b/tools/objtool/include/objtool/arch.h
    @@ -93,4 +91,6 @@ bool arch_is_rethunk(struct symbol *sym)

    int arch_rewrite_retpolines(struct objtool_file *file);

    +bool arch_pc_relative_reloc(struct reloc *reloc);
    +
    #endif /* _ARCH_H */

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