How to skip function prologues with stabs debug infomation?

Triple Yang
Sat Aug 20 03:45:00 GMT 2011

2011/8/20 Jan Kratochvil <>:
> On Fri, 19 Aug 2011 19:56:44 +0200, Triple Yang wrote:
>> It seems not that easy for a rescheduled prologue, because prologues
>> generated with compiler optimization on make things complicated.
> With gcc -O2 -g gdb already no longer skips prologues, see
> symtab->locations_valid (a recent change by me).  If DW_AT_location is valid
> for every PC of a function you do not need to skip prologues.  I would find
> best to comply with it in your compiler and do not depend on the fragile
> prologue skipping.
>> 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.
> I am not proficient with STABS but when gcc can produce the line number info
> for both STABS and DWARF you should be also able to do so.

I agree with that. Since we can get line number from binary file's
section offset, and vice versa, we can skip prologue using line
number. The practical problem is that, I don't know how to implement
it, i.e. what functions should be called. Any suggestions?

>> As for your examples, we sometimes need to skip prologue first before
>> we can insert breakpoints. Skipping prologue is a lower-level
>> function.
> I have not checked what skip_prologue_sal returns but I have checked using
> readelf -wl the breakpoint address is aligned with the line number info.
> You may have reasons for STABS but I do not see why not to produce only DWARF.
> Thanks,
> Jan

Yang Yong-Yong

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