[PATCH] riscv: add CALLER_ADDRx support

[Zong Li]

On Fri, Dec 29, 2023 at 2:34 PM Zong Li <zong.li at sifive.com> wrote:
>
> On Tue, Dec 5, 2023 at 5:00 PM Zong Li <zong.li at sifive.com> 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 at sifive.com>
> > ---
> >  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