Philippe, Peter,
Thank you for the comments. I am not even sure what the semantics of
putting a breakpoint or watchpoint
on device regions are supposed to be. I would imagine it is
architecture-specific as to whether this is even allowed.
It appears for example, that armv8-a allows watchpoints to be set on any
type of memory. armv7-a prohibits
watchpoints on Device or Strongly-ordered memory that might be accessed
by instructions multiple times
(e.g LDM and LDC instructions).
What is the current behavior for QEMU and what should
breakpoints/watchpoints do when placed on IO memory?
-perry
On 5/20/24 10:22 AM, Peter Maydell wrote:
On Wed, 15 May 2024 at 13:49, Philippe Mathieu-Daudé 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
BugLink: https://bugs.launchpad.net/qemu/+bug/1625216
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/213
Signed-off-by: Perry Hung
---
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
