Re: [PATCH] riscv: add CALLER_ADDRx support

[Zong Li]

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