[PATCH v2 1/6] riscv: Fixup __vdso_gettimeofday broke dynamic ftrace

guoren
2020-07-09T02:22:20Z

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

--
2.7.4