[Bug 1625216] Re: memory writes via gdb don't work for memory mapped hardware

[Thomas Huth]

This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/213


** Changed in: qemu
       Status: Confirmed => Expired

** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #213
   https://gitlab.com/qemu-project/qemu/-/issues/213

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https://bugs.launchpad.net/bugs/1625216

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

Status in QEMU:
  Expired

Bug description:
  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;

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