Re: [PATCH] gdb/arm: Sync sp with other *sp registers

[Luis Machado <luis.machado@arm.com>]

Hi,

On 6/30/22 08:13, Yvan Roux wrote:
> Hi,
> 
> For Arm Cortex-M33 with security extensions, there are 4 different
> stack pointers (msp_s, msp_ns, psp_s, psp_ns), without security
> extensions and for other Cortex-M targets, there are 2 different
> stack pointers (msp and psp).
> 
> This patch allows arch dependent unwinding override register values
> for registers not covered by the DWARF data.  That means that sp
> will always be in sync with one of the real stack pointers on
> Arm targets that contains more than one stack pointer.
> 
> Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
> Signed-off-by: Yvan Roux <yvan.roux@foss.st.com>
> ---
>   gdb/arm-tdep.c     | 94 ++++++++++++++++++++++++++++++++++++++++++++++
>   gdb/dwarf2/frame.c | 58 ++++++++++++++++++++++++----
>   gdb/dwarf2/frame.h |  9 +++++
>   3 files changed, 153 insertions(+), 8 deletions(-)
> 
> diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
> index 3a1b52c2380..48711cb2a65 100644
> --- a/gdb/arm-tdep.c
> +++ b/gdb/arm-tdep.c
> @@ -4956,6 +4956,98 @@ arm_dwarf2_frame_init_reg (struct gdbarch *gdbarch, int regnum,
>       }
>   }
>   
> +/* Return the value of the unspecified register REGNUM for THIS_FRAME.  */
> +
> +static struct value *
> +arm_dwarf2_frame_prev_unspecified_reg (struct frame_info *this_frame,
> +				       int regnum)
> +{
> +  struct gdbarch *gdbarch = get_frame_arch (this_frame);
> +  arm_gdbarch_tdep *tdep = (arm_gdbarch_tdep *) gdbarch_tdep (gdbarch);
> +  bool override_with_sp_value = false;
> +
> +  if (tdep->have_sec_ext)
> +    {
> +      CORE_ADDR sp, msp_s, msp_ns, psp_s, psp_ns;
> +      sp = get_frame_register_unsigned (this_frame, ARM_SP_REGNUM);
> +      msp_s = get_frame_register_unsigned (this_frame,
> +					   tdep->m_profile_msp_s_regnum);
> +      msp_ns = get_frame_register_unsigned (this_frame,
> +					    tdep->m_profile_msp_ns_regnum);
> +      psp_s = get_frame_register_unsigned (this_frame,
> +					   tdep->m_profile_psp_s_regnum);
> +      psp_ns = get_frame_register_unsigned (this_frame,
> +					    tdep->m_profile_psp_ns_regnum);
> +
> +      if (regnum == tdep->m_profile_msp_regnum && (msp_s == sp || msp_ns == sp))
> +	{
> +	  /* Use value of SP for MSP register.  */
> +	  override_with_sp_value = true;
> +	}
> +      else if (regnum == tdep->m_profile_msp_s_regnum && msp_s == sp)
> +	{
> +	  /* Use value of SP for MSP_S register.  */
> +	  override_with_sp_value = true;
> +	}
> +      else if (regnum == tdep->m_profile_msp_ns_regnum && msp_ns == sp)
> +	{
> +	  /* Use value of SP for MSP_NS register.  */
> +	  override_with_sp_value = true;
> +	}
> +      else if (regnum == tdep->m_profile_psp_regnum && (psp_s == sp
> +							|| psp_ns == sp))
> +	{
> +	  /* Use value of SP for PSP register.  */
> +	  override_with_sp_value = true;
> +	}
> +      else if (regnum == tdep->m_profile_psp_s_regnum && psp_s == sp)
> +	{
> +	  /* Use value of SP for PSP_S register.  */
> +	  override_with_sp_value = true;
> +	}
> +      else if (regnum == tdep->m_profile_psp_ns_regnum && psp_ns == sp)
> +	{
> +	  /* Use value of SP for PSP_NS register.  */
> +	  override_with_sp_value = true;
> +	}
> +    }
> +  else if (tdep->is_m)
> +    {
> +      CORE_ADDR sp, msp, psp;
> +      sp = get_frame_register_unsigned (this_frame, ARM_SP_REGNUM);
> +      msp = get_frame_register_unsigned (this_frame,
> +					 tdep->m_profile_msp_regnum);
> +      psp = get_frame_register_unsigned (this_frame,
> +					 tdep->m_profile_psp_regnum);
> +
> +      if (regnum == tdep->m_profile_msp_regnum && sp == msp)
> +	{
> +	  /* Use value of SP for MSP register.  */
> +	  override_with_sp_value = true;
> +	}
> +      else if (regnum == tdep->m_profile_psp_regnum && sp == psp)
> +	{
> +	  /* Use value of SP for PSP register.  */
> +	  override_with_sp_value = true;
> +	}
> +    }
> +
> +  if (override_with_sp_value)
> +    {
> +      CORE_ADDR prev_sp;
> +      struct frame_info *prev_frame = get_prev_frame (this_frame);
> +      if (prev_frame)
> +	prev_sp = get_frame_register_unsigned (prev_frame, ARM_SP_REGNUM);
> +      else
> +	prev_sp = get_frame_base (this_frame);
> +
> +      return frame_unwind_got_constant (this_frame, regnum, prev_sp);
> +    }
> +
> +  /* Don't know how to fetch this value, use generic method.  */
> +  return NULL;
> +}
> +
>   /* Given BUF, which is OLD_LEN bytes ending at ENDADDR, expand
>      the buffer to be NEW_LEN bytes ending at ENDADDR.  Return
>      NULL if an error occurs.  BUF is freed.  */
> @@ -10438,6 +10530,8 @@ arm_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
>     gdbarch_init_osabi (info, gdbarch);
>   
>     dwarf2_frame_set_init_reg (gdbarch, arm_dwarf2_frame_init_reg);
> +  dwarf2_frame_set_prev_unspecified_reg (gdbarch,
> +					 arm_dwarf2_frame_prev_unspecified_reg);
>   
>     /* Add some default predicates.  */
>     if (is_m)
> diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
> index 5878d72f922..c4b15b2d240 100644
> --- a/gdb/dwarf2/frame.c
> +++ b/gdb/dwarf2/frame.c
> @@ -595,6 +595,10 @@ struct dwarf2_frame_ops
>     /* Convert .eh_frame register number to DWARF register number, or
>        adjust .debug_frame register number.  */
>     int (*adjust_regnum) (struct gdbarch *, int, int);
> +
> +  /* Return the value of the unspecified register REGNUM for THIS_FRAME. */
> +  struct value * (*prev_unspecified_reg) (struct frame_info *this_frame,
> +					  int regnum);
>   };
>   
>   /* Default architecture-specific register state initialization
> @@ -677,6 +681,50 @@ dwarf2_frame_init_reg (struct gdbarch *gdbarch, int regnum,
>     ops->init_reg (gdbarch, regnum, reg, this_frame);
>   }
>   
> +/* Set the architecture-specific unspecified register unwinding
> +   function for GDBARCH to PREV_UNSPECIFIED_REG.  */
> +
> +void
> +dwarf2_frame_set_prev_unspecified_reg (struct gdbarch *gdbarch,
> +				       struct value * (*prev_unspecified_reg)
> +					      (struct frame_info *this_frame,
> +					       int regnum))
> +{
> +  struct dwarf2_frame_ops *ops
> +    = (struct dwarf2_frame_ops *) gdbarch_data (gdbarch, dwarf2_frame_data);
> +
> +  ops->prev_unspecified_reg = prev_unspecified_reg;
> +}

I'm wondering if we really need to introduce a hook here. I understand we may need to sidestep the dwarf unwinder
to do custom handling of the msp*/psp* registers, but wouldn't we be able to achieve the same with the existing
dwarf hooks?

For example, we could register a hook with dwarf2_frame_set_init_reg (), like aarch64 (see gdb/aarch64-tdep.c:aarch64_dwarf2_frame_init_reg).

With such a hook, we could define our own rules for individual registers through DWARF2_FRAME_REG_FN.

Would that work?