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    Subject[PATCH 5.8 050/464] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.
    Date
    From: Gregory Herrero <gregory.herrero@oracle.com>

    [ Upstream commit ea0eada45632f4807b2f49de951072283e2d781c ]

    Currently, if a section has a relocation to '_mcount' symbol, a new
    __mcount_loc entry will be added whatever the relocation type is.
    This is problematic when a relocation to '_mcount' is in the middle of a
    section and is not a call for ftrace use.

    Such relocation could be generated with below code for example:
    bool is_mcount(unsigned long addr)
    {
    return (target == (unsigned long) &_mcount);
    }

    With this snippet of code, ftrace will try to patch the mcount location
    generated by this code on module load and fail with:

    Call trace:
    ftrace_bug+0xa0/0x28c
    ftrace_process_locs+0x2f4/0x430
    ftrace_module_init+0x30/0x38
    load_module+0x14f0/0x1e78
    __do_sys_finit_module+0x100/0x11c
    __arm64_sys_finit_module+0x28/0x34
    el0_svc_common+0x88/0x194
    el0_svc_handler+0x38/0x8c
    el0_svc+0x8/0xc
    ---[ end trace d828d06b36ad9d59 ]---
    ftrace failed to modify
    [<ffffa2dbf3a3a41c>] 0xffffa2dbf3a3a41c
    actual: 66:a9:3c:90
    Initializing ftrace call sites
    ftrace record flags: 2000000
    (0)
    expected tramp: ffffa2dc6cf66724

    So Limit the relocation type to R_AARCH64_CALL26 as in perl version of
    recordmcount.

    Fixes: af64d2aa872a ("ftrace: Add arm64 support to recordmcount")
    Signed-off-by: Gregory Herrero <gregory.herrero@oracle.com>
    Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    Link: https://lore.kernel.org/r/20200717143338.19302-1-gregory.herrero@oracle.com
    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    scripts/recordmcount.c | 6 ++++++
    1 file changed, 6 insertions(+)

    diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
    index 7225107a9aafe..e59022b3f1254 100644
    --- a/scripts/recordmcount.c
    +++ b/scripts/recordmcount.c
    @@ -434,6 +434,11 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
    return 1;
    }

    +static int arm64_is_fake_mcount(Elf64_Rel const *rp)
    +{
    + return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
    +}
    +
    /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
    * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
    * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
    @@ -547,6 +552,7 @@ static int do_file(char const *const fname)
    make_nop = make_nop_arm64;
    rel_type_nop = R_AARCH64_NONE;
    ideal_nop = ideal_nop4_arm64;
    + is_fake_mcount64 = arm64_is_fake_mcount;
    break;
    case EM_IA_64: reltype = R_IA64_IMM64; break;
    case EM_MIPS: /* reltype: e_class */ break;
    --
    2.25.1


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