gdb/arm: Sync sp with other *sp registers

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).

With this patch, sp will always be in sync with one of the real stack
pointers on Arm targets that contain 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

@@ -3815,6 +3815,78 @@ arm_dwarf2_prev_register (struct frame_info *this_frame, void **this_cache,
       cpsr = reconstruct_t_bit (gdbarch, lr, cpsr);
       return frame_unwind_got_constant (this_frame, regnum, cpsr);
     }
+  else if (arm_is_alternative_sp_register (tdep, regnum))
+    {
+      /* Handle the alternative SP registers on Cortex-M.  */
+      bool override_with_sp_value = false;
+      CORE_ADDR val;
+
+      if (tdep->have_sec_ext)
+	{
+	  CORE_ADDR sp
+	    = get_frame_register_unsigned (this_frame, ARM_SP_REGNUM);
+	  CORE_ADDR msp_s
+	    = get_frame_register_unsigned (this_frame,
+					   tdep->m_profile_msp_s_regnum);
+	  CORE_ADDR msp_ns
+	    = get_frame_register_unsigned (this_frame,
+					   tdep->m_profile_msp_ns_regnum);
+	  CORE_ADDR psp_s
+	    = get_frame_register_unsigned (this_frame,
+					   tdep->m_profile_psp_s_regnum);
+	  CORE_ADDR psp_ns
+	    = get_frame_register_unsigned (this_frame,
+					   tdep->m_profile_psp_ns_regnum);
+
+	  bool is_msp = (regnum == tdep->m_profile_msp_regnum)
+	    && (msp_s == sp || msp_ns == sp);
+	  bool is_msp_s = (regnum == tdep->m_profile_msp_s_regnum)
+	    && (msp_s == sp);
+	  bool is_msp_ns = (regnum == tdep->m_profile_msp_ns_regnum)
+	    && (msp_ns == sp);
+	  bool is_psp = (regnum == tdep->m_profile_psp_regnum)
+	    && (psp_s == sp || psp_ns == sp);
+	  bool is_psp_s = (regnum == tdep->m_profile_psp_s_regnum)
+	    && (psp_s == sp);
+	  bool is_psp_ns = (regnum == tdep->m_profile_psp_ns_regnum)
+	    && (psp_ns == sp);
+
+	  override_with_sp_value = is_msp || is_msp_s || is_msp_ns
+	    || is_psp || is_psp_s || is_psp_ns;
+
+	}
+      else if (tdep->is_m)
+	{
+	  CORE_ADDR sp
+	    = get_frame_register_unsigned (this_frame, ARM_SP_REGNUM);
+	  CORE_ADDR msp
+	    = get_frame_register_unsigned (this_frame,
+					   tdep->m_profile_msp_regnum);
+	  CORE_ADDR psp
+	    = get_frame_register_unsigned (this_frame,
+					   tdep->m_profile_psp_regnum);
+
+	  bool is_msp = (regnum == tdep->m_profile_msp_regnum) && (sp == msp);
+	  bool is_psp = (regnum == tdep->m_profile_psp_regnum) && (sp == psp);
+
+	  override_with_sp_value = is_msp || is_psp;
+	}
+
+      if (override_with_sp_value)
+	{
+	  /* Use value of SP from previous frame.  */
+	  struct frame_info *prev_frame = get_prev_frame (this_frame);
+	  if (prev_frame)
+	    val = get_frame_register_unsigned (prev_frame, ARM_SP_REGNUM);
+	  else
+	    val = get_frame_base (this_frame);
+	}
+      else
+	/* Use value for the register from previous frame.  */
+	val = get_frame_register_unsigned (this_frame, regnum);
+
+      return frame_unwind_got_constant (this_frame, regnum, val);
+    }
 
   internal_error (__FILE__, __LINE__,
 		  _("Unexpected register %d"), regnum);
@@ -4934,6 +5006,8 @@ arm_dwarf2_frame_init_reg (struct gdbarch *gdbarch, int regnum,
 			   struct dwarf2_frame_state_reg *reg,
 			   struct frame_info *this_frame)
 {
+  arm_gdbarch_tdep *tdep = gdbarch_tdep<arm_gdbarch_tdep> (gdbarch);
+
   if (is_pacbti_pseudo (gdbarch, regnum))
     {
       /* Initialize RA_AUTH_CODE to zero.  */
@@ -4950,6 +5024,12 @@ arm_dwarf2_frame_init_reg (struct gdbarch *gdbarch, int regnum,
     }
   else if (regnum == ARM_SP_REGNUM)
     reg->how = DWARF2_FRAME_REG_CFA;
+  else if (arm_is_alternative_sp_register (tdep, regnum))
+    {
+      /* Handle the alternative SP registers on Cortex-M.  */
+      reg->how = DWARF2_FRAME_REG_FN;
+      reg->loc.fn = arm_dwarf2_prev_register;
+    }
 }
 
 /* Given BUF, which is OLD_LEN bytes ending at ENDADDR, expand