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Date:   Mon, 20 Jul 2020 18:10:56 -0700 (PDT)
Subject:     Re: [PATCH v2 1/6] riscv: Fixup __vdso_gettimeofday broke dynamic ftrace
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CC:     Paul Walmsley <paul.walmsley@sifive.com>, anup@brainfault.org,
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        mhiramat@kernel.org, linux-riscv@lists.infradead.org,
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From:   Palmer Dabbelt <palmerdabbelt@google.com>
To:     guoren@kernel.org
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On Wed, 08 Jul 2020 19:19:09 PDT (-0700), guoren@kernel.org wrote:
> From: Guo Ren <guoren@linux.alibaba.com>
>
> For linux-5.8-rc1, enable ftrace of riscv will cause boot panic:
>
> [    2.388980] Run /sbin/init as init process
> [    2.529938] init[39]: unhandled signal 4 code 0x1 at 0x0000003ff449e000
> [    2.531078] CPU: 0 PID: 39 Comm: init Not tainted 5.8.0-rc1-dirty #13
> [    2.532719] epc: 0000003ff449e000 ra : 0000003ff449e954 sp : 0000003fffedb900
> [    2.534005]  gp : 00000000000e8528 tp : 0000003ff449d800 t0 : 000000000000001e
> [    2.534965]  t1 : 000000000000000a t2 : 0000003fffedb89e s0 : 0000003fffedb920
> [    2.536279]  s1 : 0000003fffedb940 a0 : 0000003ff43d4b2c a1 : 0000000000000000
> [    2.537334]  a2 : 0000000000000001 a3 : 0000000000000000 a4 : fffffffffbad8000
> [    2.538466]  a5 : 0000003ff449e93a a6 : 0000000000000000 a7 : 0000000000000000
> [    2.539511]  s2 : 0000000000000000 s3 : 0000003ff448412c s4 : 0000000000000010
> [    2.541260]  s5 : 0000000000000016 s6 : 00000000000d0a30 s7 : 0000003fffedba70
> [    2.542152]  s8 : 0000000000000000 s9 : 0000000000000000 s10: 0000003fffedb960
> [    2.543335]  s11: 0000000000000000 t3 : 0000000000000000 t4 : 0000003fffedb8a0
> [    2.544471]  t5 : 0000000000000000 t6 : 0000000000000000
> [    2.545730] status: 0000000000004020 badaddr: 00000000464c457f cause: 0000000000000002
> [    2.549867] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
> [    2.551267] CPU: 0 PID: 1 Comm: init Not tainted 5.8.0-rc1-dirty #13
> [    2.552061] Call Trace:
> [    2.552626] [<ffffffe00020374a>] walk_stackframe+0x0/0xc4
> [    2.553486] [<ffffffe0002039f4>] show_stack+0x40/0x4c
> [    2.553995] [<ffffffe00054a6ae>] dump_stack+0x7a/0x98
> [    2.554615] [<ffffffe00020b9b8>] panic+0x114/0x2f4
> [    2.555395] [<ffffffe00020ebd6>] do_exit+0x89c/0x8c2
> [    2.555949] [<ffffffe00020f930>] do_group_exit+0x3a/0x90
> [    2.556715] [<ffffffe000219e08>] get_signal+0xe2/0x6e6
> [    2.557388] [<ffffffe000202d72>] do_notify_resume+0x6a/0x37a
> [    2.558089] [<ffffffe000201c16>] ret_from_exception+0x0/0xc
>
> "ra:0x3ff449e954" is the return address of "call _mcount" in the
> prologue of __vdso_gettimeofday(). Without proper relocate, pc jmp
> to 0x0000003ff449e000 (vdso map base) with a illegal instruction
> trap.
>
> The solution comes from arch/arm64/kernel/vdso/Makefile:
>
> CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS)
>
>  - CC_FLAGS_SCS is ShadowCallStack feature in Clang and only
>    implemented for arm64, no use for riscv.
>
> The bug comes from the following commit:
>
> ad5d1122b82f ("riscv: use vDSO common flow to reduce the latency of the time-related functions")
>
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> Reviewed-by: Pekka Enberg <penberg@kernel.org>
> Cc: Vincent Chen <vincent.chen@sifive.com>
> Cc: Atish Patra <atish.patra@wdc.com>
> Cc: Palmer Dabbelt <palmerdabbelt@google.com>
> Cc: Alan Kao <alankao@andestech.com>
> Cc: Greentime Hu <green.hu@gmail.com>
> ---
>  arch/riscv/kernel/vdso/Makefile | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
> index 38ba55b..3079935 100644
> --- a/arch/riscv/kernel/vdso/Makefile
> +++ b/arch/riscv/kernel/vdso/Makefile
> @@ -27,6 +27,9 @@ obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
>  obj-y += vdso.o vdso-syms.o
>  CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
>
> +# Disable -pg to prevent insert call site
> +CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os
> +
>  # Disable gcov profiling for VDSO code
>  GCOV_PROFILE := n

As far as I can tell this is already in Linus' tree.  LMK if I'm missing
something.