lkml.org 
[lkml]   [2020]   [May]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH][V3] arm64: perf: Get the wrong PC value in REGS_ABI_32 mode
    On Tue, May 26, 2020 at 11:26:11AM +0100, Mark Rutland wrote:
    > On Mon, May 11, 2020 at 10:52:07AM +0800, Jiping Ma wrote:
    > > Modified the patch subject and the change description.
    > >
    > > PC value is get from regs[15] in REGS_ABI_32 mode, but correct PC
    > > is regs->pc(regs[PERF_REG_ARM64_PC]) in arm64 kernel, which caused
    > > that perf can not parser the backtrace of app with dwarf mode in the
    > > 32bit system and 64bit kernel.
    > >
    > > Signed-off-by: Jiping Ma <jiping.ma2@windriver.com>
    >
    > Thanks for this.
    >
    >
    > > ---
    > > arch/arm64/kernel/perf_regs.c | 4 ++++
    > > 1 file changed, 4 insertions(+)
    > >
    > > diff --git a/arch/arm64/kernel/perf_regs.c b/arch/arm64/kernel/perf_regs.c
    > > index 0bbac61..0ef2880 100644
    > > --- a/arch/arm64/kernel/perf_regs.c
    > > +++ b/arch/arm64/kernel/perf_regs.c
    > > @@ -32,6 +32,10 @@ u64 perf_reg_value(struct pt_regs *regs, int idx)
    > > if ((u32)idx == PERF_REG_ARM64_PC)
    > > return regs->pc;
    > >
    > > + if (perf_reg_abi(current) == PERF_SAMPLE_REGS_ABI_32
    > > + && idx == 15)
    > > + return regs->pc;
    >
    > I think there are some more issues here, and we may need a more
    > substantial rework. For a compat thread, we always expose
    > PERF_SAMPLE_REGS_ABI_32 via per_reg_abi(), but for some reason
    > perf_reg_value() also munges the compat SP/LR into their ARM64
    > equivalents, which don't exist in the 32-bit sample ABI. We also don't
    > zero the regs that don't exist in 32-bit (including the aliasing PC).

    I think this was for the case where you have a 64-bit perf profiling a
    32-bit task, and it was passing the registers off to libunwind. Won't that
    break if we follow your suggestion?

    Will

    \
     
     \ /
      Last update: 2020-05-26 21:55    [W:3.130 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site