How to skip function prologues with stabs debug infomation?

Triple Yang
Sat Aug 20 03:18:00 GMT 2011

2011/8/20 Sterling Augustine <>:
> The Xtensa port uses prologue analysis (and some heuristics) to
> determine its end without debug info. It's prologues are somewhat more
> complex than others. Take a look at xtensa-tdep.c starting around line
> 1151.
> It's only a heuristic, but for unoptimized code it works pretty well.
> For optimized code, the prologue can be sufficiently mixed with real
> code and that makes it hard to declare a single point "the end of the
> prologue" anyway.

OK, I'll take it as an example. Actually I've written a skip prologue
subroutine using heuristics, which works sometimes. I am thinking to
make use of SAL to do better.

> Sterling
> On Fri, Aug 19, 2011 at 10:56 AM, Triple Yang <> wrote:
>> Thank you. Of course GDB supports SATBS debug info.
>> well, my question is mostly on HOW to support SATBS debug info
>> (specifically, to skip prologue) when I have to write a new gdb
>> backend, i.e. to port gdb to a new architecture whose function
>> prologue instructions are not that orderly.
>> I have checked several backend implementations such as or32 and i386,
>> but their prologues are tidy and clean to make the analysis much
>> easier. So we don't even need debug info to skip the prologue. It
>> seems not that easy for a rescheduled prologue, because prologues
>> generated with compiler optimization on make things complicated.
>> It's well-known that people can take advantage of SAL info when to
>> skip prologue with dwarf info. I wonder whether we can do the same
>> thing with stabs.
>> As for your examples, we sometimes need to skip prologue first before
>> we can insert breakpoints. Skipping prologue is a lower-level
>> function.
>> Best regards.
>> 2011/8/20 Jan Kratochvil <>:
>>> On Fri, 19 Aug 2011 18:08:54 +0200, Triple Yang wrote:
>>>> is there any chance that we use symbol and line (sal) to skip function
>>>> prologues with stabs debug infomation?
>>>> And if not, why?
>>> GDB does, why not?  The prologue skipping processes already decoded debug
>>> info, no matter if it is DWARF or STABS.
>>> gcc -Wall
>>> Breakpoint 1 at 0x400478
>>> gcc -gstabs
>>> Temporary breakpoint 1 at 0x40047c: file 24.c, line 3.
>>> (gdb) p/x $pc
>>> $1 = 0x40047c
>>> gcc -gdwarf-3
>>> Temporary breakpoint 1 at 0x40047c: file 24.c, line 3.
>>> Sure STABS is discouraged.
>>> Regards,
>>> Jan
>> --
>> Yang Yong-Yong

Yang Yong-Yong

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