Re: [RFA] New GDB target iq2000

Mark Kettenis
2005-03-05T11:29:42Z

Date: Fri, 4 Mar 2005 17:01:04 -0500
From: Daniel Jacobowitz <drow@false.org>

I left the other function alone. skip_prologue_using_sal is already a
bit bogus, for the reasons identified by Kevin as well as for at least
one other that I can see. find_last_line_symbol is even boguser.
Basically, any code that compares the LINE member of two arbitrary SALs
_must_ be wrong. They don't even need to be in the same source file.

Another issue with skip_prologue_using_sal() is that it will happily
skip the entire function if the function body is basically empty. I
really think it should be deprecated, and shouldn't be used in any new
code.

There's two things that GDB uses the guessed prologue line information
for. One is to place an initial breakpoint, so that the arguments have
been saved. This problem will hopefully eventually go away, with
improved GCC -fvar-tracking - we should be able to print the arguments
from anywhere. Someone needs to spend a little love on the compiler
side of this.

The important thing about placing the initial breakpoint, is that it
shouldn't be placed too far into the function. In particular it
should not end up after a branch instruction.

The other is as a limit for prologue scanners. IMO, what you need in
iq2000_scan_prologue is not line table data at all, but a list of
instructions which can not be considered part of the prologue.
Basically that is calls and branches, and a check that you only record
a register save the first time you see the register being saved.
Going too far here is not a major problem; after the patch below, I
think the call in iq2000_skip_prologue is basically redundant.
Returning FUNC_ADDR would work just about as well, since if we have no
line data, we probably have no symbolic argument information either.

Most prologue scanners indeed "know" about what conditions end a
prologue. In those cases the limit is only there to prevent the
analyzer to run away if for some reason it ends up analyzing code that
it shouldn't.

Mark