For the layman, what does this mean?
Ubuntu 24.04 LTS will enable frame pointers by default
11–20 of 121 posts
Re: Ubuntu 24.04 LTS will enable frame pointers by default
#12Thank god. AMD making the base pointer optional in the x86-64 ABI was foolish.
Re: Ubuntu 24.04 LTS will enable frame pointers by default
#13For anyone else who didn't know what a frame pointer was: https://softwareengineering.stackexchange.com/questions/1943...
Re: Ubuntu 24.04 LTS will enable frame pointers by default
#14Even in context it is hard to understand this: "The performance wins that these can provide far outweigh the comparatively tiny loss in performance."
My guess is that on average the potential performance discovered with the techniques this enables is higher than the guaranteed negligible performance loss.
Re: Ubuntu 24.04 LTS will enable frame pointers by default
#15hmm.. I wonder if the 10% performance regression in python has been resolved.
https://discuss.python.org/t/python-3-11-performance-with-fr...
Re: Ubuntu 24.04 LTS will enable frame pointers by default
#16For the layman, what does this mean?
Exciting new failure modes
Re: Ubuntu 24.04 LTS will enable frame pointers by default
#17hmm.. I wonder if the 10% performance regression in python has been resolved. https://discuss.python.org/t/python-3-11-performance-with-fr...
We’re waiting on the benchmarks once the archive has been rebuilt to double check if we’ll be affected in that way, but if indeed we do find that sort of regression, we’ll exclude Python from this change (and any other package where there is a substantial hit).
Re: Ubuntu 24.04 LTS will enable frame pointers by default
#18Even in context it is hard to understand this: "The performance wins that these can provide far outweigh the comparatively tiny loss in performance." My guess is that on average the potential performance discovered with the techniques this enables is higher than the guaranteed negligible performance loss.
Yes, that's correct.
Re: Ubuntu 24.04 LTS will enable frame pointers by default
#19For the layman, what does this mean?
Better stack traces for profiling tools when you don't have debugging symbols, or can't use them for whatever reason
Re: Ubuntu 24.04 LTS will enable frame pointers by default
#20For the layman, what does this mean?
I was going to write a long essay about the relation between C and assembly but after thinking for a while, I think there is an easier way to explain it.
Stack frames are basically a (single) linked list of information about the call stack. Every frame corresponds to one function call, and says where the local variables are stored, and where the function should return after it has finished.
The head of this list is stored in a register (a scarce resource, superfast memory). So to use frame pointers, you have to spend one register, and also every function has to do some work to maintain the linked list. Two instructions worth of work when the function is enterred, and one when it exits.
The alternative to doing this explicitly is to keep track of it all implicitly which is faster but a bit more complex.