Despite commit e207b4aa718e ("target/hppa: Drop attempted gdbstub
support for hppa64") saying that hppa-linux-gdb doesn't support 64 bit
mode via remote protocol, it is actually working with a small add-on
patch which enables gdb to guess the size from the g protocol:

$ hppa64-linux-gnu-gdb ~/seabios-hppa/out-64/hppa-firmware64.img
[..]
Reading symbols from /home/svens/seabios-hppa/out-64/hppa-firmware64.img...
(gdb) target remote :1234
Remote debugging using :1234
warning: remote target does not support file transfer, attempting to access files from local filesystem.
warning: Unable to find dynamic linker breakpoint function.
GDB will be unable to debug shared library initializers
and track explicitly loaded dynamic code.
startup () at src/parisc/head.S:144
144		rsm	PSW_I, %r0	/* disable local irqs */
(gdb)

Signed-off-by: Sven Schnelle <svens@stackframe.org>
---
 target/hppa/gdbstub.c | 32 +++++++++++++++++++-------------
 1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/target/hppa/gdbstub.c b/target/hppa/gdbstub.c
index 4a965b38d7..48a514384f 100644
--- a/target/hppa/gdbstub.c
+++ b/target/hppa/gdbstub.c
@@ -21,16 +21,11 @@
 #include "cpu.h"
 #include "gdbstub/helpers.h"
 
-/*
- * GDB 15 only supports PA1.0 via the remote protocol, and ignores
- * any provided xml.  Which means that any attempt to provide more
- * data results in "Remote 'g' packet reply is too long".
- */
-
 int hppa_cpu_gdb_read_register(CPUState *cs, GByteArray *mem_buf, int n)
 {
-    CPUHPPAState *env = cpu_env(cs);
-    uint32_t val;
+    HPPACPU *cpu = HPPA_CPU(cs);
+    CPUHPPAState *env = &cpu->env;
+    target_ureg val;
 
     switch (n) {
     case 0:
@@ -144,13 +139,24 @@ int hppa_cpu_gdb_read_register(CPUState *cs, GByteArray *mem_buf, int n)
         break;
     }
 
-    return gdb_get_reg32(mem_buf, val);
+    if (TARGET_REGISTER_BITS == 64) {
+        return gdb_get_reg64(mem_buf, val);
+    } else {
+        return gdb_get_reg32(mem_buf, val);
+    }
 }
 
 int hppa_cpu_gdb_write_register(CPUState *cs, uint8_t *mem_buf, int n)
 {
-    CPUHPPAState *env = cpu_env(cs);
-    uint32_t val = ldl_p(mem_buf);
+    HPPACPU *cpu = HPPA_CPU(cs);
+    CPUHPPAState *env = &cpu->env;
+    target_ureg val;
+
+    if (TARGET_REGISTER_BITS == 64) {
+        val = ldq_p(mem_buf);
+    } else {
+        val = ldl_p(mem_buf);
+    }
 
     switch (n) {
     case 0:
@@ -160,7 +166,7 @@ int hppa_cpu_gdb_write_register(CPUState *cs, uint8_t *mem_buf, int n)
         env->gr[n] = val;
         break;
     case 32:
-        env->cr[CR_SAR] = val & (hppa_is_pa20(env) ? 63 : 31);
+        env->cr[CR_SAR] = val;
         break;
     case 33:
         env->iaoq_f = val;
@@ -272,5 +278,5 @@ int hppa_cpu_gdb_write_register(CPUState *cs, uint8_t *mem_buf, int n)
         }
         break;
     }
-    return 4;
+    return sizeof(target_ureg);
 }
-- 
2.43.2