[CHERRY PICK] target: Fix force-reading of registers and add flush capability

Cherrry-picked form https://review.openocd.org/c/openocd/+/8070/21

1) OpenOCD has the capability to 'force' a register read from the
target. This functionality however silently breaks the register
cache: During 'get_reg force' or 'reg <name> force',
reg->type->get() is called which will silently overwrite
dirty items in the register cache, causing a loss of unwritten
register values. This patch fixes that by adding a flush
callback for registers, and by using it when it is needed.

2) The register write commands did not have the 'force' flag;
this was present for register read commands only.
This patch adds it.

3) This patch also introduces the flush_reg_cache command. It
flushes all registers and can optionally invalidate the register
cache after the flush.

For targets which implement the register cache, the flush()
callback in struct reg_arch_type should be implemented (in
separate patches, by the maintainers of each of the target type).

This functionality is also useful for test purposes. Example:
 - In RISC-V, some registers are WARL (write any read legal)
   and this command allows to check this behavior.

We plan to implement the corresponding callback
in the RISC-V target.

Change-Id: I9537a5f05b46330f70aad17f77b2b80dedad068a
Signed-off-by: Marek Vrbka <[email protected]>
Signed-off-by: Jan Matyas <[email protected]>

Author: MarekVCodasip

doc/openocd.texi

@@ -9202,7 +9202,7 @@ various operations. The current target may be changed
 by using @command{targets} command with the name of the
 target which should become current.
 
-@deffn {Command} {reg} [(number|name) [(value|'force')]]
+@deffn {Command} {reg} [(number|name)] [value] ['force']
 Access a single register by @var{number} or by its @var{name}.
 The target must generally be halted before access to CPU core
 registers is allowed. Depending on the hardware, some other
@@ -9216,15 +9216,17 @@ which are also dirty (and will be written back later)
 are flagged as such.
 
 @emph{With number/name}: display that register's value.
-Use @var{force} argument to read directly from the target,
-bypassing any internal cache.
+Use @var{force} argument to read directly from the target
+(as opposed to OpenOCD's internal register cache).
 
 @emph{With both number/name and value}: set register's value.
 Writes may be held in a writeback cache internal to OpenOCD,
 so that setting the value marks the register as dirty instead
 of immediately flushing that value. Resuming CPU execution
 (including by single stepping) or otherwise activating the
-relevant module will flush such values.
+relevant module will flush such values. The use of @var{force}
+causes the register value to be written to the target
+immediately.
 
 Cores may have surprisingly many registers in their
 Debug and trace infrastructure:
@@ -9241,10 +9243,13 @@ Debug and trace infrastructure:
 @end example
 @end deffn
 
-@deffn {Command} {set_reg} dict
-Set register values of the target.
+@deffn {Command} {set_reg} ['-force'] dict
+Set register values of the target. The new register values may be
+kept in OpenOCD's cache and not written to the target immediately
+(unless @var{-force} is used).
 
 @itemize
+@item @option{-force} ... Force immediate write of the new register values.
 @item @var{dict} ... Tcl dictionary with pairs of register names and values.
 @end itemize
 
@@ -9260,7 +9265,7 @@ set_reg @{pc 0 sp 0x1000@}
 Get register values from the target and return them as Tcl dictionary with pairs
 of register names and values.
 If option "-force" is set, the register values are read directly from the
-target, bypassing any caching.
+target, not from OpenOCD's internal cache.
 
 @itemize
 @item @var{list} ... List of register names
@@ -9274,6 +9279,13 @@ get_reg @{pc sp@}
 @end example
 @end deffn
 
+@deffn {Command} {flush_reg_cache} [-invalidate]
+Flush the internal OpenOCD's register cache - write back the dirty register values to the target.
+If @option{-invalidate} is set, also invalidate (forget) the OpenOCD's cached register values;
+therefore the next call to get_reg is guaranteed to read the fresh register value directly
+from the target.
+@end deffn
+
 @deffn {Command} {write_memory} address width data ['phys']
 This function provides an efficient way to write to the target memory from a Tcl
 script.

src/target/arc.c

@@ -293,6 +293,7 @@ static int arc_set_register(struct reg *reg, uint8_t *buf)
 static const struct reg_arch_type arc_reg_type = {
 	.get = arc_get_register,
 	.set = arc_set_register,
+	.flush = NULL,
 };
 
 /* GDB register groups. For now we support only general and "empty" */

src/target/armv4_5.c

@@ -655,6 +655,7 @@ static int armv4_5_set_core_reg(struct reg *reg, uint8_t *buf)
 static const struct reg_arch_type arm_reg_type = {
 	.get = armv4_5_get_core_reg,
 	.set = armv4_5_set_core_reg,
+	.flush = NULL,
 };
 
 struct reg_cache *arm_build_reg_cache(struct target *target, struct arm *arm)

src/target/armv7m.c

@@ -786,6 +786,7 @@ int armv7m_arch_state(struct target *target)
 static const struct reg_arch_type armv7m_reg_type = {
 	.get = armv7m_get_core_reg,
 	.set = armv7m_set_core_reg,
+	.flush = NULL,
 };
 
 /** Builds cache of architecturally defined registers.  */

src/target/armv8.c

@@ -1714,6 +1714,7 @@ static int armv8_set_core_reg(struct reg *reg, uint8_t *buf)
 static const struct reg_arch_type armv8_reg_type = {
 	.get = armv8_get_core_reg,
 	.set = armv8_set_core_reg,
+	.flush = NULL,
 };
 
 static int armv8_get_core_reg32(struct reg *reg)
@@ -1775,6 +1776,7 @@ static int armv8_set_core_reg32(struct reg *reg, uint8_t *buf)
 static const struct reg_arch_type armv8_reg32_type = {
 	.get = armv8_get_core_reg32,
 	.set = armv8_set_core_reg32,
+	.flush = NULL,
 };
 
 /** Builds cache of architecturally defined registers.  */

src/target/avr32_ap7k.c

@@ -157,6 +157,7 @@ static int avr32_set_core_reg(struct reg *reg, uint8_t *buf)
 static const struct reg_arch_type avr32_reg_type = {
 	.get = avr32_get_core_reg,
 	.set = avr32_set_core_reg,
+	.flush = NULL,
 };
 
 static struct reg_cache *avr32_build_reg_cache(struct target *target)

src/target/cortex_m.c

@@ -2429,6 +2429,7 @@ static const struct dwt_reg dwt_comp[] = {
 static const struct reg_arch_type dwt_reg_type = {
 	.get = cortex_m_dwt_get_reg,
 	.set = cortex_m_dwt_set_reg,
+	.flush = NULL,
 };
 
 static void cortex_m_dwt_addreg(struct target *t, struct reg *r, const struct dwt_reg *d)

src/target/dsp563xx.c

@@ -430,6 +430,7 @@ static int dsp563xx_set_core_reg(struct reg *reg, uint8_t *buf)
 static const struct reg_arch_type dsp563xx_reg_type = {
 	.get = dsp563xx_get_core_reg,
 	.set = dsp563xx_set_core_reg,
+	.flush = NULL,
 };
 
 static void dsp563xx_build_reg_cache(struct target *target)

src/target/embeddedice.c

@@ -152,6 +152,7 @@ static int embeddedice_get_reg(struct reg *reg)
 static const struct reg_arch_type eice_reg_type = {
 	.get = embeddedice_get_reg,
 	.set = embeddedice_set_reg_w_exec,
+	.flush = NULL,
 };
 
 /**

src/target/esirisc.c

@@ -1419,6 +1419,7 @@ static int esirisc_set_reg(struct reg *reg, uint8_t *buf)
 static const struct reg_arch_type esirisc_reg_type = {
 	.get = esirisc_get_reg,
 	.set = esirisc_set_reg,
+	.flush = NULL,
 };
 
 static struct reg_cache *esirisc_build_reg_cache(struct target *target)

src/target/etb.c

@@ -108,6 +108,7 @@ static int etb_get_reg(struct reg *reg)
 static const struct reg_arch_type etb_reg_type = {
 	.get = etb_get_reg,
 	.set = etb_set_reg_w_exec,
+	.flush = NULL,
 };
 
 struct reg_cache *etb_build_reg_cache(struct etb *etb)

src/target/etm.c

@@ -215,6 +215,7 @@ static int etm_write_reg(struct reg *reg, uint32_t value);
 static const struct reg_arch_type etm_scan6_type = {
 	.get = etm_get_reg,
 	.set = etm_set_reg_w_exec,
+	.flush = NULL,
 };
 
 /* Look up register by ID ... most ETM instances only

src/target/lakemont.c

@@ -357,6 +357,7 @@ static const struct reg_arch_type lakemont_reg_type = {
 	 */
 	.get = lakemont_get_core_reg,
 	.set = lakemont_set_core_reg,
+	.flush = NULL,
 };
 
 struct reg_cache *lakemont_build_reg_cache(struct target *t)

src/target/mem_ap.c

@@ -179,6 +179,7 @@ static int mem_ap_reg_set(struct reg *reg, uint8_t *buf)
 static struct reg_arch_type mem_ap_reg_arch_type = {
 	.get = mem_ap_reg_get,
 	.set = mem_ap_reg_set,
+	.flush = NULL,
 };
 
 static const char *mem_ap_get_gdb_arch(const struct target *target)

src/target/mips32.c

@@ -496,6 +496,7 @@ int mips32_arch_state(struct target *target)
 static const struct reg_arch_type mips32_reg_type = {
 	.get = mips32_get_core_reg,
 	.set = mips32_set_core_reg,
+	.flush = NULL,
 };
 
 struct reg_cache *mips32_build_reg_cache(struct target *target)

src/target/mips64.c

@@ -370,6 +370,7 @@ int mips64_arch_state(struct target *target)
 static const struct reg_arch_type mips64_reg_type = {
 	.get = mips64_get_core_reg,
 	.set = mips64_set_core_reg,
+	.flush = NULL,
 };
 
 int mips64_build_reg_cache(struct target *target)

src/target/openrisc/or1k.c

@@ -494,6 +494,7 @@ static int or1k_set_core_reg(struct reg *reg, uint8_t *buf)
 static const struct reg_arch_type or1k_reg_type = {
 	.get = or1k_get_core_reg,
 	.set = or1k_set_core_reg,
+	.flush = NULL,
 };
 
 static struct reg_cache *or1k_build_reg_cache(struct target *target)

src/target/register.c

@@ -14,6 +14,8 @@
 
 #include "register.h"
 #include <helper/log.h>
+#include <target/target.h>
+#include <target/target_type.h>
 
 /**
  * @file
@@ -115,12 +117,72 @@ static int register_set_dummy_core_reg(struct reg *reg, uint8_t *buf)
 	return ERROR_OK;
 }
 
+static int register_flush_dummy(struct reg *reg)
+{
+	reg->dirty = false;
+
+	return ERROR_OK;
+}
+
 static const struct reg_arch_type dummy_type = {
 	.get = register_get_dummy_core_reg,
 	.set = register_set_dummy_core_reg,
+	.flush = register_flush_dummy,
 };
 
 void register_init_dummy(struct reg *reg)
 {
 	reg->type = &dummy_type;
 }
+
+int register_flush(const struct target *target, struct reg *reg, bool invalidate)
+{
+	if (!reg) {
+		LOG_ERROR("BUG: %s called with NULL", __func__);
+		return ERROR_FAIL;
+	}
+
+	if (!reg->exist) {
+		LOG_ERROR("BUG: %s called with non-existent register", __func__);
+		return ERROR_FAIL;
+	}
+
+	if (!reg->dirty) {
+		LOG_TARGET_DEBUG(target, "Register '%s' is not dirty, nothing to flush", reg->name);
+		if (reg->valid && invalidate) {
+			LOG_TARGET_DEBUG(target, "Invalidating register '%s'", reg->name);
+			reg->valid = false;
+		}
+		return ERROR_OK;
+	}
+
+	if (!reg->type->flush) {
+		LOG_TARGET_ERROR(target, "Unable to flush dirty register '%s' - operation not yet supported "
+			"by %s implementation in OpenOCD", reg->name, target->type->name);
+		return ERROR_NOT_IMPLEMENTED;
+	}
+
+	if (!reg->valid) {
+		LOG_ERROR("BUG: Register '%s' is not valid, but flush attempted", reg->name);
+		return ERROR_FAIL;
+	}
+
+	LOG_TARGET_DEBUG(target, "Flushing register '%s'", reg->name);
+
+	int result = reg->type->flush(reg);
+	if (result != ERROR_OK) {
+		LOG_TARGET_ERROR(target, "Failed to flush register '%s'", reg->name);
+		return result;
+	}
+
+	if (reg->dirty) {
+		LOG_ERROR("BUG: Register '%s' remained dirty after flushing", reg->name);
+		return ERROR_FAIL;
+	}
+	if (reg->valid && invalidate) {
+		LOG_TARGET_DEBUG(target, "Invalidating register '%s' after flush", reg->name);
+		reg->valid = false;
+	}
+
+	return ERROR_OK;
+}

src/target/register.h

@@ -151,6 +151,7 @@ struct reg_cache {
 struct reg_arch_type {
 	int (*get)(struct reg *reg);
 	int (*set)(struct reg *reg, uint8_t *buf);
+	int (*flush)(struct reg *reg);
 };
 
 struct reg *register_get_by_number(struct reg_cache *first,
@@ -163,4 +164,7 @@ void register_cache_invalidate(struct reg_cache *cache);
 
 void register_init_dummy(struct reg *reg);
 
+/* Flushes the register. Also invalidates the cached register value if invalidate == true */
+int register_flush(const struct target *target, struct reg *reg, bool invalidate);
+
 #endif /* OPENOCD_TARGET_REGISTER_H */

src/target/stm8.c

@@ -1180,6 +1180,7 @@ static int stm8_get_gdb_reg_list(struct target *target, struct reg **reg_list[],
 static const struct reg_arch_type stm8_reg_type = {
 	.get = stm8_get_core_reg,
 	.set = stm8_set_core_reg,
+	.flush = NULL,
 };
 
 static struct reg_cache *stm8_build_reg_cache(struct target *target)