[RFC v2 1/2] riscv: allow resume after exception

[Xiang W]

Thank you, I understand.

Regards,
Xiang W

Heinrich Schuchardt <heinrich.schuchardt at canonical.com> 于2023年10月31日周二 20:09写道：
>
> On 10/31/23 09:53, Xiang W wrote:
> > setjmp can be called in set_resume.
>
> Unfortunately this is not possible. A longjmp buffer only stores
> register values and not the stack content.
>
> Let's assume that setjmp() is moved into set_resume():
>
> Let a function call set_resume(). The caller's address will be on the
> stack. Once the set_resume returns and the caller invokes another
> function the original stack content will be overwritten. When an
> exception occurs the longjmp will reenter set_resume() with the original
> stack pointer value pointing to a stack that does not match the original
> call to set_resume and set_resume will return to a random address.
>
> Best regards
>
> Heinrich
>
> >
> > Regards,
> > Xiang W
> >
> > Heinrich Schuchardt <heinrich.schuchardt at canonical.com> 于2023年10月29日周日 16:56写道：
> >>
> >> If CSRs like seed are readable by S-mode, may not be determinable by
> >> S-mode. For safe driver probing allow to resume via a longjmp after an
> >> exception.
> >>
> >> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> >> ---
> >> v2:
> >>          new patch
> >> ---
> >>   arch/riscv/lib/interrupts.c | 13 +++++++++++++
> >>   include/interrupt.h         | 22 ++++++++++++++++++++++
> >>   2 files changed, 35 insertions(+)
> >>   create mode 100644 include/interrupt.h
> >>
> >> diff --git a/arch/riscv/lib/interrupts.c b/arch/riscv/lib/interrupts.c
> >> index 02dbcfd423..a26ccc721f 100644
> >> --- a/arch/riscv/lib/interrupts.c
> >> +++ b/arch/riscv/lib/interrupts.c
> >> @@ -12,6 +12,7 @@
> >>   #include <linux/compat.h>
> >>   #include <efi_loader.h>
> >>   #include <hang.h>
> >> +#include <interrupt.h>
> >>   #include <irq_func.h>
> >>   #include <asm/global_data.h>
> >>   #include <asm/ptrace.h>
> >> @@ -21,6 +22,13 @@
> >>
> >>   DECLARE_GLOBAL_DATA_PTR;
> >>
> >> +static struct resume_data *resume;
> >> +
> >> +void set_resume(struct resume_data *data)
> >> +{
> >> +       resume = data;
> >> +}
> >> +
> >>   static void show_efi_loaded_images(uintptr_t epc)
> >>   {
> >>          efi_print_image_infos((void *)epc);
> >> @@ -105,6 +113,11 @@ static void _exit_trap(ulong code, ulong epc, ulong tval, struct pt_regs *regs)
> >>                  "Store/AMO page fault",
> >>          };
> >>
> >> +       if (resume) {
> >> +               resume->code = code;
> >> +               longjmp(resume->jump, 1);
> >> +       }
> >> +
> >>          if (code < ARRAY_SIZE(exception_code))
> >>                  printf("Unhandled exception: %s\n", exception_code[code]);
> >>          else
> >> diff --git a/include/interrupt.h b/include/interrupt.h
> >> new file mode 100644
> >> index 0000000000..1baa60bcf2
> >> --- /dev/null
> >> +++ b/include/interrupt.h
> >> @@ -0,0 +1,22 @@
> >> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> >> +
> >> +#include <asm/setjmp.h>
> >> +
> >> +/**
> >> + * struct resume_data - data for resume after interrupt
> >> + */
> >> +struct resume_data {
> >> +       /** @jump: longjmp buffer */
> >> +       jmp_buf jump;
> >> +       /** @code: exception code */
> >> +       ulong code;
> >> +};
> >> +
> >> +/**
> >> + * set_resume() - set longjmp buffer for resuming after interrupt
> >> + *
> >> + * When resuming the exception code will be returned in @data->code.
> >> + *
> >> + * @data:      pointer to structure with longjmp address
> >> + */
> >> +void set_resume(struct resume_data *data);
> >> --
> >> 2.40.1
> >>
>