• Alexey Brodkin's avatar
    ARC: make sure instruction_pointer() returns unsigned value · c7bc7995
    Alexey Brodkin authored
    commit f51e2f19 upstream.
    
    Currently instruction_pointer() returns pt_regs->ret and so return value
    is of type "long", which implicitly stands for "signed long".
    
    While that's perfectly fine when dealing with 32-bit values if return
    value of instruction_pointer() gets assigned to 64-bit variable sign
    extension may happen.
    
    And at least in one real use-case it happens already.
    In perf_prepare_sample() return value of perf_instruction_pointer()
    (which is an alias to instruction_pointer() in case of ARC) is assigned
    to (struct perf_sample_data)->ip (which type is "u64").
    
    And what we see if instuction pointer points to user-space application
    that in case of ARC lays below 0x8000_0000 "ip" gets set properly with
    leading 32 zeros. But if instruction pointer points to kernel address
    space that starts from 0x8000_0000 then "ip" is set with 32 leadig
    "f"-s. I.e. id instruction_pointer() returns 0x8100_0000, "ip" will be
    assigned with 0xffff_ffff__8100_0000. Which is obviously wrong.
    
    In particular that issuse broke output of perf, because perf was unable
    to associate addresses like 0xffff_ffff__8100_0000 with anything from
    /proc/kallsyms.
    
    That's what we used to see:
     ----------->8----------
      6.27%  ls       [unknown]                [k] 0xffffffff8046c5cc
      2.96%  ls       libuClibc-0.9.34-git.so  [.] memcpy
      2.25%  ls       libuClibc-0.9.34-git.so  [.] memset
      1.66%  ls       [unknown]                [k] 0xffffffff80666536
      1.54%  ls       libuClibc-0.9.34-git.so  [.] 0x000224d6
      1.18%  ls       libuClibc-0.9.34-git.so  [.] 0x00022472
     ----------->8----------
    
    With that change perf output looks much better now:
     ----------->8----------
      8.21%  ls       [kernel.kallsyms]        [k] memset
      3.52%  ls       libuClibc-0.9.34-git.so  [.] memcpy
      2.11%  ls       libuClibc-0.9.34-git.so  [.] malloc
      1.88%  ls       libuClibc-0.9.34-git.so  [.] memset
      1.64%  ls       [kernel.kallsyms]        [k] _raw_spin_unlock_irqrestore
      1.41%  ls       [kernel.kallsyms]        [k] __d_lookup_rcu
     ----------->8----------
    Signed-off-by: default avatarAlexey Brodkin <abrodkin@synopsys.com>
    Cc: arc-linux-dev@synopsys.com
    Cc: linux-kernel@vger.kernel.org
    Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
    Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
    c7bc7995
ptrace.h 2.75 KB