ghostty memleak detection with bpf

ghostty-memleak.md

Replicate ghostty memleak as suggested here. This works only on Linux with bcc-tools package installated.

Modify your current ghostty config file to have a very small scrollback limit. This ensures you hit the pruning logic immediately.

# Most likely in ~/.config/ghostty/config file
scrollback-limit = 100

Below code forces ghostty to non-standard page allocation. Run this on ghostty terminal (that doesn't contain the fix)

import sys
import time

# A string heavy with emojis sequences to force non-standard page allocation
complex_line = "👨‍👩‍👧‍👦 " * 50

print(f"Starting leak generation... (Press Ctrl+C to stop)")
try:
    i = 0
    while True:
        # Print the complex line with an index to keep lines unique
        sys.stdout.write(f"{i} {complex_line}\n")

        # Flush to ensure it hits the terminal immediately
        sys.stdout.flush()

        i += 1
        time.sleep(0.001)
except KeyboardInterrupt:
    print("\nStopped.")

I am using memleak bpf program to detect the leak (preferably in another terminal). Identify the pid of the ghostty process & pass it as an argument to memleak

sudo memleak-bpfcc -p <pid-of-ghostty> --combined-only
Attaching to pid 199300, Ctrl+C to quit.
[16:33:04] Top 10 stacks with outstanding allocations:
0 bytes in 0 allocations from stack
[unknown] [ghostty]
3408 bytes in 3 allocations from stack
[unknown] [ghostty]
...blah-blah....
2097152 bytes in 1 allocations from stack
[unknown] [ghostty]
1607151616 bytes in 170 allocations from stack ###around 1.6 GB leak
[unknown] [ghostty]

This is an attempt to replicate on Linux & detect the same with eBPF based on discussion here.