GDB Python API: Create hardware breakpoint object

Question

The gdb python API defines the gdb.BP_BREAKPOINT flag to use when creating a gdb.Breakpoint object, but there doesn't seem to be a flag that allows a hardware breakpoint to be set? Am I missing something?

I'd like to create a gdb.Breakpoint object so that I can override the stop method and react to breakpoints as they're triggered. As far as I can tell, there isn't a way to do this otherwise.

Interestingly enough, if I set a breakpoint the 'normal' way (eg, break *0x400123), then gdb.breakpoints() returns an object. However, if I set a hardware breakpoint the same way (hbreak *0x400123), no objects are returned. This seems to indicate that the python API can't access/manipulate HW breakpoints directly?

Using GDB 8.3.50.20190824-30.fc31 on Fedora 31.

Marco · Accepted Answer · 2021-01-21 18:03:50Z

1

I had this same problem recently. I found a hacky workaround to force gdb to use hardware breakpoints.

There's the gdb auto-hw setting, that lets gdb decide whether to insert hardware or software breakpoints automatically. This setting should be on by default.

If gdb isn't able to set a software breakpoint because the memory region is not writable, it will insert a hardware breakpoint. You can define a non-writable memory region by issuing the mem command.

mem 0 0xffffffffffffffff ro

And then your script can create all the breakpoints it wants :) (well, at least all the breakpoints the processor allows it to create)

After the breakpoints are inserted, you can go back to normal memory regions by doing mem auto.

This issue has been recently solved. So we can expect it will be available in a future release of gdb :)

edited Jan 21, 2021 at 18:03

answered Jan 16, 2021 at 23:42

Marco

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Dustin Spicuzza · Accepted Answer · 2020-02-28 18:13:07Z

0

Haven't found a way to do this using the gdb.Breakpoint, but I've got a workaround instead.

offset = 0x400123

gdb.execute("hbreak *" + hex(offset))

while True:
    gdb.execute("continue")
    value = int(gdb.parse_and_eval("$pc"))
    if value == offset:
        # respond to hardware breakpoint here
    else:
        # something else happened??

It's not perfect, but meets my current needs.

answered Feb 28, 2020 at 18:13

Dustin Spicuzza

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