target: cortex_m: add support of ARMv8.1-M register 'vpr'

The register 'vpr' is present when MVFR1.MVE is not zero.
For the moment, reuse the existing flag 'fp_feature'. To be
reviewed for the case of MVE supported without floating point.

The documentation of GDB [1] reports that the register 'vpr'
should be represented as 3 fields.

Tested on Cortex-M55 based STM32N6570.

Change-Id: I8737a24d01a13eeb09a0f2075b96be400f9f91c6
Signed-off-by: Antonio Borneo <[email protected]>
Link: [1] https://sourceware.org/gdb/download/onlinedocs/gdb.html/ARM-Features.html#M_002dprofile-Vector-Extension-_0028MVE_0029
Reviewed-on: https://review.openocd.org/c/openocd/+/8681
Tested-by: jenkins

Author: borneoa

src/target/armv7m.c

@@ -65,6 +65,28 @@ const int armv7m_msp_reg_map[ARMV7M_NUM_CORE_REGS] = {
 	ARMV7M_XPSR,
 };
 
+static struct reg_data_type_bitfield armv8m_vpr_bits[] = {
+	{  0, 15, REG_TYPE_UINT },
+	{ 16, 19, REG_TYPE_UINT },
+	{ 20, 23, REG_TYPE_UINT },
+};
+
+static struct reg_data_type_flags_field armv8m_vpr_fields[] = {
+	{ "P0",     armv8m_vpr_bits + 0, armv8m_vpr_fields + 1, },
+	{ "MASK01", armv8m_vpr_bits + 1, armv8m_vpr_fields + 2, },
+	{ "MASK23", armv8m_vpr_bits + 2, NULL },
+};
+
+static struct reg_data_type_flags armv8m_vpr_flags[] = {
+	{ 4, armv8m_vpr_fields },
+};
+
+static struct reg_data_type armv8m_flags_vpr[] = {
+	{ REG_TYPE_ARCH_DEFINED, "vpr_reg", REG_TYPE_CLASS_FLAGS,
+		{ .reg_type_flags = armv8m_vpr_flags },
+	},
+};
+
 /*
  * These registers are not memory-mapped.  The ARMv7-M profile includes
  * memory mapped registers too, such as for the NVIC (interrupt controller)
@@ -158,6 +180,8 @@ static const struct {
 	{ ARMV7M_D15, "d15", 64, REG_TYPE_IEEE_DOUBLE, "float", "org.gnu.gdb.arm.vfp", NULL, },
 
 	{ ARMV7M_FPSCR, "fpscr", 32, REG_TYPE_INT, "float", "org.gnu.gdb.arm.vfp", NULL, },
+
+	{ ARMV8M_VPR, "vpr", 32, REG_TYPE_INT, "float", "org.gnu.gdb.arm.m-profile-mve", armv8m_flags_vpr, },
 };
 
 #define ARMV7M_NUM_REGS ARRAY_SIZE(armv7m_regs)
@@ -273,6 +297,9 @@ uint32_t armv7m_map_id_to_regsel(unsigned int arm_reg_id)
 	case ARMV7M_FPSCR:
 		return ARMV7M_REGSEL_FPSCR;
 
+	case ARMV8M_VPR:
+		return ARMV8M_REGSEL_VPR;
+
 	case ARMV7M_D0 ... ARMV7M_D15:
 		return ARMV7M_REGSEL_S0 + 2 * (arm_reg_id - ARMV7M_D0);
 

src/target/armv7m.h

@@ -62,6 +62,7 @@ enum {
 	ARMV7M_REGSEL_PMSK_BPRI_FLTMSK_CTRL = 0x14,
 	ARMV8M_REGSEL_PMSK_BPRI_FLTMSK_CTRL_S = 0x22,
 	ARMV8M_REGSEL_PMSK_BPRI_FLTMSK_CTRL_NS = 0x23,
+	ARMV8M_REGSEL_VPR = 0x24,
 	ARMV7M_REGSEL_FPSCR = 0x21,
 
 	/* 32bit Floating-point registers */
@@ -196,12 +197,15 @@ enum {
 	/* Floating-point status register */
 	ARMV7M_FPSCR,
 
+	/* Vector Predication Status and Control Register */
+	ARMV8M_VPR,
+
 	/* for convenience add registers' block delimiters */
 	ARMV7M_LAST_REG,
 	ARMV7M_CORE_FIRST_REG = ARMV7M_R0,
 	ARMV7M_CORE_LAST_REG = ARMV7M_XPSR,
 	ARMV7M_FPU_FIRST_REG = ARMV7M_D0,
-	ARMV7M_FPU_LAST_REG = ARMV7M_FPSCR,
+	ARMV7M_FPU_LAST_REG = ARMV8M_VPR,
 	ARMV8M_FIRST_REG = ARMV8M_MSP_NS,
 	ARMV8M_LAST_REG = ARMV8M_CONTROL_NS,
 };

src/target/cortex_m.c

@@ -2708,6 +2708,10 @@ int cortex_m_examine(struct target *target)
 			for (size_t idx = ARMV7M_FPU_FIRST_REG; idx <= ARMV7M_FPU_LAST_REG; idx++)
 				armv7m->arm.core_cache->reg_list[idx].exist = false;
 
+		/* TODO: MVE can be present without floating points. Revisit this test */
+		if (armv7m->fp_feature != FPV5_MVE_F && armv7m->fp_feature != FPV5_MVE_I)
+			armv7m->arm.core_cache->reg_list[ARMV8M_VPR].exist = false;
+
 		if (!cortex_m_has_tz(target))
 			for (size_t idx = ARMV8M_FIRST_REG; idx <= ARMV8M_LAST_REG; idx++)
 				armv7m->arm.core_cache->reg_list[idx].exist = false;