From: Andy Chiu <andy.chiu@xxxxxxxxxx>
In RISCV, we must use an AUIPC + JALR pair to encode an immediate,
forming a jump that jumps to an address over 4K. This may cause errors
if we want to enable kernel preemption and remove dependency from
patching code with stop_machine(). For example, if a task was switched
out on auipc. And, if we changed the ftrace function before it was
switched back, then it would jump to an address that has updated 11:0
bits mixing with previous XLEN:12 part.
p: patched area performed by dynamic ftrace
ftrace_prologue:
p| REG_S ra, -SZREG(sp)
p| auipc ra, 0x? ------------> preempted
...
change ftrace function
...
p| jalr -?(ra) <------------- switched back
p| REG_L ra, -SZREG(sp)
func:
xxx
ret
Fixes: fc76b8b8011 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")
Cc: Andy Chiu <andy.chiu@xxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
---
@Andy, could you give the patch a Signed-off-by? I just copy your most
important comment, so the first author should be you. First, let's fix
the problem caused by my previous patch, and you can continue your
ftrace preemption work.
---
arch/riscv/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index ed66c31e4655..b3454c843932 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -272,7 +272,7 @@ config ARCH_RV64I
select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
select HAVE_FUNCTION_GRAPH_TRACER
- select HAVE_FUNCTION_TRACER if !XIP_KERNEL
+ select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
select SWIOTLB if MMU
endchoice
--
2.36.1
