[PATCH v2 16/50] monitor/hmp: Handle gdb-xml exposed registers via gdb_get_register()

[Philippe Mathieu-Daudé]

Implement the gdb_get_register() helper and call it before the
regular get_monitor_def() one. Registers is exposed via the
GDB XML files will be directly handled, possibily allowing new
registers added to XML files to be automatically accessible in
QEMU monitor. All targets having GDB XML files can now be used
within the monitor.

For example with Loongarch, before:

  $ qemu-system-loongarch64 -M virt -S -monitor stdio
  QEMU 10.2.0 monitor - type 'help' for more information

  (qemu) info registers

  CPU#0
   PC=000000001c000000  FCSR0 0x00000000
   ...

  (qemu) p/x $pc
  unknown register
  Try "help p" for more information
  (qemu)

and after:

  $ ./qemu-system-loongarch64 -M virt -S -monitor stdio
  QEMU 10.2.50 monitor - type 'help' for more information
  (qemu) p/x $pc
  0x1c000000
  (qemu)

Similarly RISC-V:

  QEMU 10.2.0 monitor - type 'help' for more information
  (qemu) p/x $pc
  unknown register
  Try "help p" for more information

VS

  QEMU 10.2.50 monitor - type 'help' for more information
  (qemu) p/x $pc
  0x1000
  (qemu)

Reviewed-by: Dr. David Alan Gilbert <d...@treblig.org>
Signed-off-by: Philippe Mathieu-Daudé <phi...@linaro.org>
---
TODO (Dave on v1):
add more checks on the return size of
gdb_read_register(..) just in case any arch is a bit screwy
(e.g. if they're 0 for example?)
---
 monitor/hmp.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 46 insertions(+), 3 deletions(-)

diff --git a/monitor/hmp.c b/monitor/hmp.c
index 0a5bbf82197..0e5913fabb1 100644
--- a/monitor/hmp.c
+++ b/monitor/hmp.c
@@ -27,14 +27,18 @@
 #include "hw/core/qdev.h"
 #include "monitor-internal.h"
 #include "monitor/hmp.h"
+#include "monitor/hmp-target.h"
 #include "qobject/qdict.h"
 #include "qobject/qnum.h"
+#include "qemu/bswap.h"
 #include "qemu/config-file.h"
 #include "qemu/ctype.h"
 #include "qemu/cutils.h"
 #include "qemu/log.h"
 #include "qemu/option.h"
+#include "qemu/target-info.h"
 #include "qemu/units.h"
+#include "exec/gdbstub.h"
 #include "system/block-backend.h"
 #include "trace.h"
 
@@ -306,6 +310,46 @@ void hmp_help_cmd(Monitor *mon, const char *name)
     free_cmdline_args(args, nb_args);
 }
 
+/*
+ * Set @pval to the value in the register identified by @name.
+ * return %true if the register is found, %false otherwise.
+ */
+static bool gdb_get_register(Monitor *mon, int64_t *pval, const char *name)
+{
+    g_autoptr(GArray) regs = NULL;
+    CPUState *cs = mon_get_cpu(mon);
+
+    if (cs == NULL) {
+        return false;
+    }
+
+    regs = gdb_get_register_list(cs);
+
+    for (int i = 0; i < regs->len; i++) {
+        GDBRegDesc *reg = &g_array_index(regs, GDBRegDesc, i);
+        g_autoptr(GByteArray) buf = NULL;
+        int reg_size;
+
+        if (!reg->name || g_strcmp0(name, reg->name)) {
+            continue;
+        }
+
+        buf = g_byte_array_new();
+        reg_size = gdb_read_register(cs, buf, reg->gdb_reg);
+        if (reg_size > sizeof(*pval)) {
+            return false;
+        }
+
+        if (target_big_endian()) {
+            *pval = ldn_be_p(buf->data, reg_size);
+        } else {
+            *pval = ldn_le_p(buf->data, reg_size);
+        }
+        return true;
+    }
+    return false;
+}
+
 /*******************************************************************/
 
 static const char *pch;
@@ -338,7 +382,6 @@ static int64_t expr_unary(Monitor *mon)
 {
     int64_t n;
     char *p;
-    int ret;
 
     switch (*pch) {
     case '+':
@@ -393,8 +436,8 @@ static int64_t expr_unary(Monitor *mon)
                 pch++;
             }
             *q = 0;
-            ret = get_monitor_def(mon, &reg, buf);
-            if (ret < 0) {
+            if (!gdb_get_register(mon, &reg, buf)
+                && get_monitor_def(mon, &reg, buf) < 0) {
                 expr_error(mon, "unknown register");
             }
             n = reg;
-- 
2.52.0