[2/2] RISC-V: Linux signal frame support.

  Add support for recognizing signal trampolines, parsing the signal frame,
and reading register values from it.

	gdb/
	* riscv-linux-tdep.c: Include tramp-frame.h and trad-frame.h.
	(riscv_linux_sigframe_init): Declare.
	(RISCV_INST_LI_A7_SIGRETURN, RISCV_INT_ECALL): New.
	(riscv_linux_sigframe): New.
	(SIGFRAME_SIGINFO_SIZE, UCONTEXT_MCONTEXT_OFFSET): New.
	(riscv_linux_sigframe_init): Define.
	(riscv_linux_init_abi): Call tramp_frame_prepend_unwinder.
---
 gdb/riscv-linux-tdep.c | 80 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)
  

On Thu, 25 Oct 2018 17:00:30 -0700
Jim Wilson <jimw@sifive.com> wrote:

> Add support for recognizing signal trampolines, parsing the signal frame,
> and reading register values from it.
> 
> 	gdb/
> 	* riscv-linux-tdep.c: Include tramp-frame.h and trad-frame.h.
> 	(riscv_linux_sigframe_init): Declare.
> 	(RISCV_INST_LI_A7_SIGRETURN, RISCV_INT_ECALL): New.
> 	(riscv_linux_sigframe): New.
> 	(SIGFRAME_SIGINFO_SIZE, UCONTEXT_MCONTEXT_OFFSET): New.
> 	(riscv_linux_sigframe_init): Define.
> 	(riscv_linux_init_abi): Call tramp_frame_prepend_unwinder.

Hi Jim,

Though I don't claim any knowledge of the RISC-V architecture, I
read through your patch and it looks reasonable to me.

Kevin
  

On 10/25/18 5:00 PM, Jim Wilson wrote:
> Add support for recognizing signal trampolines, parsing the signal frame,
> and reading register values from it.
> 
> 	gdb/
> 	* riscv-linux-tdep.c: Include tramp-frame.h and trad-frame.h.
> 	(riscv_linux_sigframe_init): Declare.
> 	(RISCV_INST_LI_A7_SIGRETURN, RISCV_INT_ECALL): New.
> 	(riscv_linux_sigframe): New.
> 	(SIGFRAME_SIGINFO_SIZE, UCONTEXT_MCONTEXT_OFFSET): New.
> 	(riscv_linux_sigframe_init): Define.
> 	(riscv_linux_init_abi): Call tramp_frame_prepend_unwinder.
> ---
>  gdb/riscv-linux-tdep.c | 80 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 80 insertions(+)
> 
> diff --git a/gdb/riscv-linux-tdep.c b/gdb/riscv-linux-tdep.c
> index d072c0b754..ece75dba47 100644
> --- a/gdb/riscv-linux-tdep.c
> +++ b/gdb/riscv-linux-tdep.c
> @@ -23,6 +23,8 @@
>  #include "linux-tdep.h"
>  #include "solib-svr4.h"
>  #include "regset.h"
> +#include "tramp-frame.h"
> +#include "trad-frame.h"
>  
>  /* Define the general register mapping.  The kernel puts the PC at offset 0,
>     gdb puts it at offset 32.  Register x0 is always 0 and can be ignored.
> @@ -56,6 +58,82 @@ riscv_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
>    /* TODO: Add FP register support.  */
>  }
>  
> +/* Signal trampoline support.  */
> +
> +static void riscv_linux_sigframe_init (const struct tramp_frame *self,
> +				       struct frame_info *this_frame,
> +				       struct trad_frame_cache *this_cache,
> +				       CORE_ADDR func);
> +
> +#define RISCV_INST_LI_A7_SIGRETURN	0x08b00893
> +#define RISCV_INST_ECALL		0x00000073
> +
> +static const struct tramp_frame riscv_linux_sigframe = {
> +  SIGTRAMP_FRAME,
> +  4,
> +  {
> +    { RISCV_INST_LI_A7_SIGRETURN, ULONGEST_MAX },
> +    { RISCV_INST_ECALL, ULONGEST_MAX },
> +    { TRAMP_SENTINEL_INSN }
> +  },
> +  riscv_linux_sigframe_init,
> +  NULL
> +};
> +
> +/* Runtime signal frames look like this:
> +   struct rt_sigframe {
> +     struct siginfo info;
> +     struct ucontext uc;
> +   };
> +
> +   struct ucontext {
> +     unsigned long __uc_flags;
> +     struct ucontext *uclink;
> +     stack_t uc_stack;
> +     sigset_t uc_sigmask;
> +     char __glibc_reserved[1024 / 8 - sizeof (sigset_t)];
> +     mcontext_t uc_mcontext;
> +   }; */
> +
> +#define SIGFRAME_SIGINFO_SIZE		128
> +#define UCONTEXT_MCONTEXT_OFFSET	176
> +
> +static void
> +riscv_linux_sigframe_init (const struct tramp_frame *self,
> +			   struct frame_info *this_frame,
> +			   struct trad_frame_cache *this_cache,
> +			   CORE_ADDR func)
> +{
> +  struct gdbarch *gdbarch = get_frame_arch (this_frame);
> +  int xlen = riscv_isa_xlen (gdbarch);
> +  int flen = riscv_isa_flen (gdbarch);
> +  CORE_ADDR frame_sp = get_frame_sp (this_frame);
> +  CORE_ADDR mcontext_base;
> +  CORE_ADDR regs_base;
> +
> +  mcontext_base = frame_sp + SIGFRAME_SIGINFO_SIZE + UCONTEXT_MCONTEXT_OFFSET;
> +
> +  /* Handle the integer registers.  The first one is PC, followed by x1
> +     through x31.  */
> +  regs_base = mcontext_base;
> +  trad_frame_set_reg_addr (this_cache, RISCV_PC_REGNUM, regs_base);
> +  for (int i = 1; i < 32; i++)
> +    trad_frame_set_reg_addr (this_cache, RISCV_ZERO_REGNUM + i,
> +			     regs_base + (i * xlen));
> +
> +  /* Handle the FP registers.  First comes the 32 FP registers, followed by
> +     fcsr.  */
> +  regs_base += 32 * xlen;
> +  for (int i = 0; i < 32; i++)
> +    trad_frame_set_reg_addr (this_cache, RISCV_FIRST_FP_REGNUM + i,
> +			     regs_base + (i * flen));
> +  regs_base += 32 * flen;
> +  trad_frame_set_reg_addr (this_cache, RISCV_CSR_FCSR_REGNUM, regs_base);
> +
> +  /* Choice of the bottom of the sigframe is somewhat arbitrary.  */
> +  trad_frame_set_id (this_cache, frame_id_build (frame_sp, func));

FYI, I recently added a new function to the trad_frame interface that lets you
re-use a register map instead of open-coding the layout of registers.  In this
case the logic isn't too complex, but you could simplify the handling for the
first register bank to just be:

    trad_frame_set_reg_regmap (this_cache, riscv_linux_gregmap, regs_base,
			       33 * riscv_isa_xlen (gdbarch));

(I added this new function when writing the signal frame unwinder for
riscv-fbsd-tdep.c because I was tired of duplicating the same logic for
various signal frame unwinders.)

You can see an example of this in the riscv_fbsd_sigframe_init() in
riscv-fbsd-tdep.c.  (For FreeBSD I also use a register map for the fp
registers since FreeBSD is dumping those in a core dump note as well.)