llvm dev - Apr 2011 - [LLVMdev] Transition C->bitcode->assembly->object looses frame pointers

Hi Alexander, while I can reproduce the problem with your example,
inspection of the assembler shows that the frame pointer is being
correctly set up in each function.  So I don't think the problem
is due to frame pointer elimination.

Ciao, Duncan.

Hi Alexander, I took a look at how backtrace works and it doesn't use
the frame pointer at all, instead it uses dwarf unwind tables.  So to
make it work using llc you need to do as follows:

$ llc -unwind-tables bt.ll -o bt.S
$ gcc -o bt-llc bt.S
$ ./bt-llc 4
backtrace() returned 4 addresses
./bt-llc() [0x4007aa]
./bt-llc() [0x400856]
./bt-llc() [0x40087c]
./bt-llc() [0x400875]

Ciao, Duncan.

Hi Duncan,

I really had to look into backtrace internals before asking.
Thank you very much!

Alexander

On Tue, Apr 5, 2011 at 6:24 PM, Duncan Sands
<duncan.sands at math.u-psud.fr> wrote:
> Hi Alexander, I took a look at how backtrace works and it doesn't use
> the frame pointer at all, instead it uses dwarf unwind tables.  So to
> make it work using llc you need to do as follows:
>
> $ llc -unwind-tables bt.ll -o bt.S
> $ gcc -o bt-llc bt.S
> $ ./bt-llc 4
> backtrace() returned 4 addresses
> ./bt-llc() [0x4007aa]
> ./bt-llc() [0x400856]
> ./bt-llc() [0x40087c]
> ./bt-llc() [0x400875]
>
> Ciao, Duncan.
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