On Wed, 15 May 2024 at 13:49, Philippe Mathieu-Daudé <phi...@linaro.org> wrote:
>
> Hi Perry,
>
> On 14/5/24 01:33, Perry Hung wrote:
> > Writes from GDB to memory-mapped IO regions are currently silently
> > dropped. cpu_memory_rw_debug() calls address_space_write_rom(), which
> > calls address_space_write_rom_internal(), which ignores all non-ram/rom
> > regions.
> >
> > Add a check for MMIO regions and direct those to address_space_rw()
> > instead.
> >
>
> Reported-by: Andreas Rasmusson <andreas.rasmus...@gmail.com>
> BugLink: https://bugs.launchpad.net/qemu/+bug/1625216
>
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/213
> > Signed-off-by: Perry Hung <pe...@mosi.io>
> > ---
> > system/physmem.c | 5 ++++-
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/system/physmem.c b/system/physmem.c
> > index 342b7a8fd4..013cdd2ab1 100644
> > --- a/system/physmem.c
> > +++ b/system/physmem.c
> > @@ -3508,7 +3508,10 @@ int cpu_memory_rw_debug(CPUState *cpu, vaddr addr,
> > if (l > len)
> > l = len;
> > phys_addr += (addr & ~TARGET_PAGE_MASK);
> > - if (is_write) {
> > + if (cpu_physical_memory_is_io(phys_addr)) {
> > + res = address_space_rw(cpu->cpu_ases[asidx].as, phys_addr,
> > attrs,
> > + buf, l, is_write);
> > + } else if (is_write) {
> > res = address_space_write_rom(cpu->cpu_ases[asidx].as,
> > phys_addr,
> > attrs, buf, l);
> > } else {
The other option is to make address_space_write_rom_internal()
also write to devices...
> I wonder if we shouldn't be safer with a preliminary patch
> adding a 'can_do_io' boolean argument to cpu_memory_rw_debug()
> (updating the call sites), then this patch would become:
>
> if (can_do_io && cpu_physical_memory_is_io(phys_addr)) {
>
> One of my worries for example is if someone accidently insert
> a breakpoint at a I/O address, the device might change its
> state and return MEMTX_OK which is confusing.
You can definitely do some silly things if we remove this
restriction.
On the other hand if you're using gdb as a debugger on real
(bare metal) hardware does anything stop you doing that?
-- PMM
