• Gregory Herrero's avatar
    recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64. · ea0eada4
    Gregory Herrero authored
    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: af64d2aa ("ftrace: Add arm64 support to recordmcount")
    Signed-off-by: default avatarGregory Herrero <gregory.herrero@oracle.com>
    Acked-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
    Link: https://lore.kernel.org/r/20200717143338.19302-1-gregory.herrero@oracle.comSigned-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    ea0eada4
recordmcount.c 16.7 KB