Re: [PATCH] riscv: add CALLER_ADDRx support

[Zong Li]

On Wed, Jan 31, 2024 at 10:46 PM Alexandre Ghiti <alex@xxxxxxxx> wrote:
>
> Hi Zong,
>
> On 31/01/2024 15:24, Zong Li wrote:
> > On Thu, Jan 18, 2024 at 8:50 AM Zong Li <zong.li@xxxxxxxxxx> wrote:
> >> On Wed, Jan 10, 2024 at 11:33 AM Zong Li <zong.li@xxxxxxxxxx> wrote:
> >>> On Fri, Dec 29, 2023 at 2:34 PM Zong Li <zong.li@xxxxxxxxxx> wrote:
> >>>> On Tue, Dec 5, 2023 at 5:00 PM Zong Li <zong.li@xxxxxxxxxx> wrote:
> >>>>> CALLER_ADDRx returns caller's address at specified level, they are used
> >>>>> for several tracers. These macros eventually use
> >>>>> __builtin_return_address(n) to get the caller's address if arch doesn't
> >>>>> define their own implementation.
> >>>>>
> >>>>> In RISC-V, __builtin_return_address(n) only works when n == 0, we need
> >>>>> to walk the stack frame to get the caller's address at specified level.
> >>>>>
> >>>>> data.level started from 'level + 3' due to the call flow of getting
> >>>>> caller's address in RISC-V implementation. If we don't have additional
> >>>>> three iteration, the level is corresponding to follows:
> >>>>>
> >>>>> callsite -> return_address -> arch_stack_walk -> walk_stackframe
> >>>>> |           |                 |                  |
> >>>>> level 3     level 2           level 1            level 0
> >>>>>
> >>>>> Signed-off-by: Zong Li <zong.li@xxxxxxxxxx>
> >>>>> ---
> >>>>>   arch/riscv/include/asm/ftrace.h    |  5 ++++
> >>>>>   arch/riscv/kernel/Makefile         |  2 ++
> >>>>>   arch/riscv/kernel/return_address.c | 48 ++++++++++++++++++++++++++++++
> >>>>>   3 files changed, 55 insertions(+)
> >>>>>   create mode 100644 arch/riscv/kernel/return_address.c
> >>>>>
> >>>>> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> >>>>> index 2b2f5df7ef2c..42777f91a9c5 100644
> >>>>> --- a/arch/riscv/include/asm/ftrace.h
> >>>>> +++ b/arch/riscv/include/asm/ftrace.h
> >>>>> @@ -25,6 +25,11 @@
> >>>>>
> >>>>>   #define ARCH_SUPPORTS_FTRACE_OPS 1
> >>>>>   #ifndef __ASSEMBLY__
> >>>>> +
> >>>>> +extern void *return_address(unsigned int level);
> >>>>> +
> >>>>> +#define ftrace_return_address(n) return_address(n)
> >>>>> +
> >>>>>   void MCOUNT_NAME(void);
> >>>>>   static inline unsigned long ftrace_call_adjust(unsigned long addr)
> >>>>>   {
> >>>>> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> >>>>> index fee22a3d1b53..40d054939ae2 100644
> >>>>> --- a/arch/riscv/kernel/Makefile
> >>>>> +++ b/arch/riscv/kernel/Makefile
> >>>>> @@ -7,6 +7,7 @@ ifdef CONFIG_FTRACE
> >>>>>   CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
> >>>>>   CFLAGS_REMOVE_patch.o  = $(CC_FLAGS_FTRACE)
> >>>>>   CFLAGS_REMOVE_sbi.o    = $(CC_FLAGS_FTRACE)
> >>>>> +CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE)
> >>>>>   endif
> >>>>>   CFLAGS_syscall_table.o += $(call cc-option,-Wno-override-init,)
> >>>>>   CFLAGS_compat_syscall_table.o += $(call cc-option,-Wno-override-init,)
> >>>>> @@ -46,6 +47,7 @@ obj-y += irq.o
> >>>>>   obj-y  += process.o
> >>>>>   obj-y  += ptrace.o
> >>>>>   obj-y  += reset.o
> >>>>> +obj-y  += return_address.o
> >>>>>   obj-y  += setup.o
> >>>>>   obj-y  += signal.o
> >>>>>   obj-y  += syscall_table.o
> >>>>> diff --git a/arch/riscv/kernel/return_address.c b/arch/riscv/kernel/return_address.c
> >>>>> new file mode 100644
> >>>>> index 000000000000..c2008d4aa6e5
> >>>>> --- /dev/null
> >>>>> +++ b/arch/riscv/kernel/return_address.c
> >>>>> @@ -0,0 +1,48 @@
> >>>>> +// SPDX-License-Identifier: GPL-2.0-only
> >>>>> +/*
> >>>>> + * This code come from arch/arm64/kernel/return_address.c
> >>>>> + *
> >>>>> + * Copyright (C) 2023 SiFive.
> >>>>> + */
> >>>>> +
> >>>>> +#include <linux/export.h>
> >>>>> +#include <linux/kprobes.h>
> >>>>> +#include <linux/stacktrace.h>
> >>>>> +
> >>>>> +struct return_address_data {
> >>>>> +       unsigned int level;
> >>>>> +       void *addr;
> >>>>> +};
> >>>>> +
> >>>>> +static bool save_return_addr(void *d, unsigned long pc)
> >>>>> +{
> >>>>> +       struct return_address_data *data = d;
> >>>>> +
> >>>>> +       if (!data->level) {
> >>>>> +               data->addr = (void *)pc;
> >>>>> +               return false;
> >>>>> +       }
> >>>>> +
> >>>>> +       --data->level;
> >>>>> +
> >>>>> +       return true;
> >>>>> +}
> >>>>> +NOKPROBE_SYMBOL(save_return_addr);
> >>>>> +
> >>>>> +void *return_address(unsigned int level)
> >>>>> +{
> >>>>> +       struct return_address_data data;
> >>>>> +
> >>>>> +       data.level = level + 3;
> >>>>> +       data.addr = NULL;
> >>>>> +
> >>>>> +       arch_stack_walk(save_return_addr, &data, current, NULL);
> >>>>> +
> >>>>> +       if (!data.level)
> >>>>> +               return data.addr;
> >>>>> +       else
> >>>>> +               return NULL;
> >>>>> +
> >>>>> +}
> >>>>> +EXPORT_SYMBOL_GPL(return_address);
> >>>>> +NOKPROBE_SYMBOL(return_address);
> >>>>> --
> >>>>> 2.17.1
> >>>>>
> >>>> Hi Palmer and all,
> >>>> I was wondering whether this patch is good for everyone? Thanks
> >>> Hi Palmer,
> >>> Is there any chance to include this patch in 6.8-rc1? Thanks
> >> Hi Palmer,
> >> I'm not sure if this patch is a feature or bug fix, would you consider
> >> it for 6.8-rcX? Thanks
> > Hi Palmer,
> > Sorry for pinging you again. I'm not sure if you saw this patch. The
> > irqsoff and wakeup tracer will use CALLER_ADDR1 and CALLER_ADDR2 to
> > obtain the caller's return address, but we are currently encountering
> > an issue in the RISC-V port where the wrong caller is identified. I
> > guess you can easily reproduce the situation using ftrace. Could you
> > share your thoughts on this when you have the time to take a look?
> > Thanks
>
>
> I'm not Palmer but I'll take a look at your patch today :)
>

Hi Alexandre,

I appreciate your assistance in reviewing this patch, Thanks a lot. :)

> Thanks,
>
> Alex
>
>
> >
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