memory writes via gdb don't work for memory mapped hardware

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1625216
Reported by 'Andreas Rasmusson' on 2016-09-19 :

When I remote-debug a qemu-guest and attempt to write to a memory mapped
location, the
write-handler for the concerned device will not be called. All write-
requiests from
gdb are delegated to cpu_physical_memory_write_rom(...). a function that
writes to the
underlying ram-block.

I believe requests to memory mapped hardware should be delegated to
address_space_rw().

example:
;; a memory mapped device. No effect, the write-handler is not called
(gdb) set *0xfff3c000 = 48

;; a ram or rom-block. Thos works. The value is changed.
(gdb) set *0x100000 = 48


----------------------------------------

Here's my suggested patch. As noted in the comment, it could perhaps be
improved for the (rare) case when the write-request from gdb spans
multiple
memory regions.

$ git diff   85bc2a15121e8bcd9f15eb75794a1eacca9d84bd HEAD ../exec.c
diff --git a/exec.c b/exec.c
index c4f9036..45ef896 100644
--- a/exec.c
+++ b/exec.c
@@ -3676,6 +3676,7 @@ int cpu_memory_rw_debug(CPUState *cpu, target_ulong
addr,
     int l;
     hwaddr phys_addr;
     target_ulong page;
+    bool is_memcpy_access;

     while (len > 0) {
         int asidx;
@@ -3691,13 +3692,32 @@ int cpu_memory_rw_debug(CPUState *cpu,
target_ulong addr,
         if (l > len)
             l = len;
         phys_addr += (addr & ~TARGET_PAGE_MASK);
+
         if (is_write) {
+            /* if ram/rom region we access the memory
+               via memcpy instead of via the cpu */
+            hwaddr mr_len, addr1;
+            AddressSpace *as = cpu->cpu_ases[asidx].as;
+            MemoryRegion *mr = address_space_translate(as, phys_addr,
&addr1, &mr_len, is_write);
+            is_memcpy_access  = memory_region_is_ram(mr) ||
memory_region_is_romd(mr);
+            if(mr_len < len) {
+                /* TODO, mimic more of the loop over mr chunks as
+                   done in cpu_physical_memory_write_internal */
+                printf("warning: we dont know whether all bytes "
+                       "to be written are ram/rom or io\n");
+            }
+        }
+        else {
+            is_memcpy_access = false;
+        }
+
+        if (is_write && is_memcpy_access) {
             cpu_physical_memory_write_rom(cpu->cpu_ases[asidx].as,
                                           phys_addr, buf, l);
         } else {
             address_space_rw(cpu->cpu_ases[asidx].as, phys_addr,
                              MEMTXATTRS_UNSPECIFIED,
-                             buf, l, 0);
+                             buf, l, is_write);
         }
         len -= l;
         buf += l;