GDB without traditional frames

GDB without traditional frames

[Andrew Cagney]

Hello,

As an accademic exercise I decided to see what would happen if a PPC64 
GDB was configured to only use dwarf2 cfi (just disable the trad-frame 
code).

The short answer is "it works (mostly)".

The long answer is ...

It relies on there being 100% coverage of the CFI.  System libraries can 
sometimes be lacking.  Assembler stubs, for instance, will trip things 
up.  Irony here is that it's those same assembler routines that trip up 
traditional unwinders.  Anyway, an unwinder capable of unwinding just LR 
works pretty well.

GCC CFI leaves registers as "unspecified" and the "assume same value" 
hack isn't sufficient.  For PPC64, GCC points the "return_column" at 
dwarf2 num 65 (that's the FPSCR but lets ignore that m'key :-).  It 
needs to specify that by default the "return_column" has the same value 
as the "LR" column.

So while trad unwind code is useful, I think it can now be considered 
largely optional.

I've got more GCC bugs to file :-)

enjoy,
Andrew

GDB without traditional frames

[Andrew Cagney]

Hello,

As an accademic exercise I decided to see what would happen if a PPC64 
GDB was configured to only use dwarf2 cfi (just disable the trad-frame 
code).

The short answer is "it works (mostly)".

The long answer is ...

It relies on there being 100% coverage of the CFI.  System libraries can 
sometimes be lacking.  Assembler stubs, for instance, will trip things 
up.  Irony here is that it's those same assembler routines that trip up 
traditional unwinders.  Anyway, an unwinder capable of unwinding just LR 
works pretty well.

GCC CFI leaves registers as "unspecified" and the "assume same value" 
hack isn't sufficient.  For PPC64, GCC points the "return_column" at 
dwarf2 num 65 (that's the FPSCR but lets ignore that m'key :-).  It 
needs to specify that by default the "return_column" has the same value 
as the "LR" column.

So while trad unwind code is useful, I think it can now be considered 
largely optional.

I've got more GCC bugs to file :-)

enjoy,
Andrew

Re: GDB without traditional frames

[y2bismil]

Hey all,

not sure if you remember, but I was trying to get a binary compiled on
Openwatcom 1.0 to be debugged using GDB.  Anyways, from what I can gather,

Watcom used a draft standard for their DWARF format
Unix International Programming Languages SIG, Version 2, Draft 6, dated April
12, 1993

Just to see if its a quick fix that could be made, I was wondering if anyone
knows the exact document GDB's DWARF abilities are based on.  

Thanks all,

Yamin

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Re: GDB without traditional frames

[Daniel Berlin]

On Sep 26, 2003, at 5:19 PM, y2bismil@engmail.uwaterloo.ca wrote:

> Hey all,
>
> not sure if you remember, but I was trying to get a binary compiled on
> Openwatcom 1.0 to be debugged using GDB.  Anyways, from what I can 
> gather,
>
> Watcom used a draft standard for their DWARF format
> Unix International Programming Languages SIG, Version 2, Draft 6, 
> dated April
> 12, 1993
>

First of all, DWARF 2.0 reached non-draft form, so i'm not sure why 
they use a draft version of the standard.


> Just to see if its a quick fix that could be made, I was wondering if 
> anyone
> knows the exact document GDB's DWARF abilities are based on.
>

GDB supports DWARF 2.0, as well as some of the draft DWARF 3.0.

Please send a binary made with openwatcom so we can look at it and see 
what's up.

>