C development

Debugging

Compilation flags to enable debug

gcc -O0 -g exec.c -o exec

Enable core dumps on Ubuntu

sudo sysctl -w kernel.core_pattern=core.%p

Next, set ulimit in the shell, where you run your program

ulimit -c unlimited

Core dumps will be side by side with executable.

LLDB

Commands

b FunctionName – set breakpoint
bt – backtrace
n – next
s – step in
c – continue
p – print variable or expression
expr – evaluate and print expression
Enter – previous command repeat

Read core-dumps

lldb --core /cores/core.30993

lldb /path/to/executable -c /path/to/core.2731

Select frame

(lldb) fr sel 4
(lldb) f 4

Print binary or hex

(lldb) p/t (uint32)((35184372088832) >> 32) & 0xffff
(unsigned int) $0 = 0b00000000000000000010000000000000

(lldb) p/x 100500
(int) $2 = 0x00018894

Print memory block by pointer

(lldb) memory read --size 1 --format x --count 256 pointer

Change signal handling rules (e.g. allow SIGINT pass)

(lldb) pro hand -p true SIGINT
NAME         PASS   STOP   NOTIFY
===========  =====  =====  ======
SIGINT       true   true   true 

Profiling

Flamegraphs

More info

dtrace

By pid

sudo dtrace -x ustackframes=100 -n 'profile-99 /pid == 21898  && arg1/ {@[ustack()] = count(); } tick-60s { exit(0); }' -o out.stacks

sudo dtrace -x ustackframes=100 -n 'profile-99 /execname == "postgres" && arg1/ {@[ustack()] = count(); } tick-60s { exit(0); }' -p 21800  -o out.stacks

By process name

sudo dtrace -x ustackframes=100 -n 'profile-99 /execname == "postgres" && arg1/ {@[ustack()] = count(); } tick-60s { exit(0); }' -o out.stacks

Create SVG

~/dev/FlameGraph/stackcollapse.pl out.stacks > out.folded

~/dev/FlameGraph/flamegraph.pl out.folded > out.svg

perf

By pid

sudo perf record -p 12345 -F 99 -g

mv perf.data my_prog_perf.data

Create SVG

sudo perf script -i my_prog_perf.data | ~/dev/FlameGraph/stackcollapse-perf.pl > my_prog_perf_out.perf-folded

~/dev/FlameGraph/flamegraph.pl my_prog_perf_out.perf-folded > my_prog_perf.svg