Subject: re: GDB breakpoints / alpha
To: Nathan J. Williams <nathanw@MIT.EDU>
From: matthew green <>
List: tech-toolchain
Date: 12/11/2000 11:47:46
   > i'm trying to port gdb-current to the alpha, using the gnu/dist/gdb
   > alpha bits.  i've finally gotten to the stage where it links and
   > runs, but breakpoints don't work.  they just ignored.
   > i'm fairly gdb clueless -- anyone have any ideas on where to begin looking?
   When I was debugging a similar problem, I made heavy use of ktrace(1)
   on gdb, keeping an eye on calls to ptrace(2). Setting a breakpoint is
   done with a PT_READ_I to read the original instruction at a location,
   followed by a PT_WRITE_D to set the instruction to something that
   causes a breakpoint trap. (since the kernel does the same thing for _D
   and _I ptrace requests, this inconsistency doesn't matter).
   On the Alpha, gdb should be writing 0x00000080, which is the bpt
   instruction (really a CALL_PAL bpt instruction); this comes out of the
   BREAKPOINT define in gdb/config/alpha/tm-alpha.h.

ok, thanks for the hint.  gdb isn't making _any_ PT_WRITE_D calls for
setting breakpoints.  it _is_ able to read & write child memory, however,
so these calls are working.... it's just for some reason, it never is.

next step:  why?