Warning: Too many CFI instuctions

[Mark Wielaard]

Hi Torsten,

On Sun, Nov 25, 2018 at 10:31:33PM +0100, Torsten Polle wrote:
> I get the following warning when calculating backtraces with SystemTap: "Too many CFI instuctions“. Therefore I change the output of the warning to print out the number of needed instructions.
> 
> Too many CFI instuctions: 723
> Too many CFI instuctions: 967
> Too many CFI instuctions: 571
> Too many CFI instuctions: 555
> Too many CFI instuctions: 2167
> Too many CFI instuctions: 883
> Too many CFI instuctions: 647
> Too many CFI instuctions: 2691
> Too many CFI instuctions: 787
> Too many CFI instuctions: 931
> Too many CFI instuctions: 1627
> Too many CFI instuctions: 751
> Too many CFI instuctions: 615
> Too many CFI instuctions: 1283
> Too many CFI instuctions: 619
> Too many CFI instuctions: 663
> Too many CFI instuctions: 727
> Too many CFI instuctions: 759
> Too many CFI instuctions: 579
> Too many CFI instuctions: 527
> Too many CFI instuctions: 959
> Too many CFI instuctions: 1091
> Too many CFI instuctions: 1335
> Too many CFI instuctions: 515
> Too many CFI instuctions: 843
> Too many CFI instuctions: 1567
> Too many CFI instuctions: 671
> Too many CFI instuctions: 539
> Too many CFI instuctions: 991
> Too many CFI instuctions: 823
> Too many CFI instuctions: 1211
> Too many CFI instuctions: 627
> Too many CFI instuctions: 667
> Too many CFI instuctions: 695
> Too many CFI instuctions: 639
> Too many CFI instuctions: 691
> Too many CFI instuctions: 635
> Too many CFI instuctions: 587
> Too many CFI instuctions: 2299
> Too many CFI instuctions: 1019
> Too many CFI instuctions: 763
> Too many CFI instuctions: 547
> Too many CFI instuctions: 523
> Too many CFI instuctions: 1095
> Too many CFI instuctions: 771
> Too many CFI instuctions: 543
> Too many CFI instuctions: 875
> Too many CFI instuctions: 2223
> Too many CFI instuctions: 535
> Too many CFI instuctions: 903
> Too many CFI instuctions: 799
> Too many CFI instuctions: 755
> Too many CFI instuctions: 1219
> Too many CFI instuctions: 867
> Too many CFI instuctions: 592
> Too many CFI instuctions: 611
> Too many CFI instuctions: 5547
> Too many CFI instuctions: 1847
> 
> Consequently, I increase the maximum to 8192 in runtime/unwind.c.
> #define MAX_CFI 8192
> 
> As a result SystemTap behaves as expected.
> 
> Would it be possible to either increase the size or make it configurable?

We could certainly make it larger and/or configurable.
Probably using it as:

#ifndef MAX_CFI
#define MAX_CFI 512
#endif

would make it possible to just use stap -DMAX_CFI=8192
(untested)

But what has 5000+ CFI instructions? That seems excessive.
As the comment says:

/* Limit the number of instructions we process. Arbitrary limit.
   512 should be enough for anybody... */

Apparently 512 isn't enough for everybody :)
But I am really curious what CFI is so big.

Thanks,

Mark