Re: [PATCH] riscv: Fixup __vdso_gettimeofday broke dynamic ftrace

[Vincent Chen <vincent.chen@sifive.com>]

On Tue, Jun 23, 2020 at 9:27 PM Greentime Hu <green.hu@gmail.com> wrote:
>
> <guoren@kernel.org> 於 2020年6月23日 週二 下午5:52寫道：
> >
> > 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>
> > 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
> >
>
> Thank you, Guo.
> I encounter the same bug in v5.8-rc2.
> This patch works.
>
> Tested-by: Greentime Hu <greentime.hu@sifive.com>

Sorry for any inconvenience caused by my mistake and thank you for
resolving this bug.
It looks good to me.
Reviewed-by: Vincent Chen <vincent.chen@sifive.com>