debug-optimized-builds

Name: debug-optimized-builds
Author: mohitmishra786

288installs19forks

How to install debug-optimized-builds?

mohitmishra786/low-level-dev-skills/debug-optimized-builds

$npx -y skills add mohitmishra786/low-level-dev-skills --skill debug-optimized-builds

Installs into the current project.

Summary

Debugging optimized builds skill for diagnosing issues in release code. Use when debugging RelWithDebInfo builds, using -Og for debuggable optimization, working with split-DWARF, applying GDB scheduler-locking, reading inlined frames, or understanding "value optimized out" messag

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SKILL.md

1	# Debugging Optimized Builds
2
3	## Purpose
4
5	Guide agents through debugging code compiled with optimization: choosing the right debug-friendly optimization level, reading inlined frames, diagnosing "value optimized out", using split-DWARF for faster debug builds, and applying GDB techniques specific to optimized code.
6
7	## Triggers
8
9	- "GDB says 'value optimized out' — what does that mean?"
10	- "How do I debug a release build?"
11	- "How do I see inlined function frames in GDB?"
12	- "What's the difference between -O0 and -Og for debugging?"
13	- "How do I use RelWithDebInfo with CMake?"
14	- "Breakpoints in optimized code land on wrong lines"
15
16	## Workflow
17
18	### 1. Choose the right build configuration
19
20	```
21	Goal?
22	├── Full debuggability, no optimization
23	│ → -O0 -g (slowest, all vars visible)
24	├── Debuggable, some optimization (recommended for most dev work)
25	│ → -Og -g (-Og keeps debug experience good)
26	├── Release build with debug info (shipped, debuggable crashes)
27	│ → -O2 -g -gsplit-dwarf (or -O2 -g1 for lighter info)
28	└── Full release (no debug symbols)
29	→ -O2 -DNDEBUG
30	```
31
32	`-Og`: GCC's "debug-friendly optimization" — enables optimizations that don't interfere with debugging. Variables stay in registers where GDB can see them. Line numbers stay accurate. Best balance for development.
33
34	```bash
35	# GCC / Clang
36	gcc -Og -g -Wall main.c -o prog
37
38	# CMake build types
39	cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug # -O0 -g
40	cmake -S . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo # -O2 -g -DNDEBUG
41	cmake -S . -B build -DCMAKE_BUILD_TYPE=Release # -O2 -DNDEBUG
42	```
43
44	### 2. "Value optimized out" — causes and workarounds
45
46	```text
47	(gdb) print my_variable
48	$1 = <optimized out>
49	```
50
51	This means the compiler decided the variable's value doesn't need to be stored at this point — it might be:
52	- Kept only in a register (not the one GDB is looking at)
53	- Folded into a constant by constant propagation
54	- Eliminated because it's not used after this point
55	- Replaced by a later optimized value
56
57	Workarounds:
58
59	```c
60	// 1. Mark variable volatile (prevents optimization away)
61	volatile int counter = 0;
62	// Use sparingly — changes semantics
63
64	// 2. Use GCC attribute
65	int counter __attribute__((used)) = 0;
66
67	// 3. Compile problematic TU at lower optimization
68	// In CMake:
69	set_source_files_properties(tricky.c PROPERTIES COMPILE_FLAGS "-O0")
70
71	// 4. Use -Og instead of -O2 for the whole build
72
73	// 5. Look at register values directly
74	// (gdb) info registers
75	// (gdb) p/x $rax # value may be in a register
76	```
77
78	### 3. Reading inlined frames in GDB
79
80	With optimization, frequently-called small functions get inlined. GDB shows these as extra frames:
81
82	```text
83	(gdb) bt
84	#0 process_packet (data=0x7ff..., len=<optimized out>)
85	at network.c:45
86	#1 0x0000... in dispatch_handler (pkt=0x7ff...)
87	at handler.c:102
88	#2 (inlined by) event_loop () at main.c:78
89	#3 0x0000... in main () at main.c:200
90
91	# (inlined by) frames are virtual — they show the call chain
92	# that was inlined into the actual frame above
93	```
94
95	```bash
96	# Navigate inlined frames
97	(gdb) frame 2 # jump to the inlined frame
98	(gdb) up # move up through frames (including inlined)
99	(gdb) down # move down
100
101	# Show all frames including inlined
102	(gdb) backtrace full
103
104	# Set breakpoint inside inlined function
105	(gdb) break network.c:45 # may hit multiple inlined call sites
106	(gdb) break process_packet # hits all inline expansions
107	```
108
109	### 4. Line number discrepancies
110
111	Optimizers reorder instructions, so the "current line" in GDB may jump around:
112
113	```bash
114	# See which instructions map to which source lines
115	(gdb) disassemble /s function_name # interleaved source and asm
116
117	# Step by machine instruction (more accurate in optimized code)
118	(gdb) si # stepi — one machine instruction
119	(gdb) ni # nexti — one machine instruction (no step into)
120
121	# Show mixed source/asm at current point
122	(gdb) layout split # TUI mode: source + asm side by side
123	(gdb) set disassemble-next-line on
124
125	# Jump to specific address (when line stepping is unreliable)
126	(gdb) jump *0x400a2c
127	```
128
129	### 5. GDB scheduler-locking for optimized multithreaded code
130
131	With optimization, threads may race in unexpected ways when stepping:
132
133	```bash
134	# Lock the scheduler — only the current thread runs while stepping
135	(gdb) set scheduler-locking on
136
137	# Modes:
138	# off — all threads run freely (default)
139	# on — only current thread runs while stepping
140	# step — only

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debug-optimized-builds

288installs19forks

View on GitHub

How to install debug-optimized-builds?

mohitmishra786/low-level-dev-skills/debug-optimized-builds

$npx -y skills add mohitmishra786/low-level-dev-skills --skill debug-optimized-builds

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# Debugging Optimized Builds
2
3	## Purpose
4
5	Guide agents through debugging code compiled with optimization: choosing the right debug-friendly optimization level, reading inlined frames, diagnosing "value optimized out", using split-DWARF for faster debug builds, and applying GDB techniques specific to optimized code.
6
7	## Triggers
8
9	- "GDB says 'value optimized out' — what does that mean?"
10	- "How do I debug a release build?"
11	- "How do I see inlined function frames in GDB?"
12	- "What's the difference between -O0 and -Og for debugging?"
13	- "How do I use RelWithDebInfo with CMake?"
14	- "Breakpoints in optimized code land on wrong lines"
15
16	## Workflow
17
18	### 1. Choose the right build configuration
19
20	```
21	Goal?
22	├── Full debuggability, no optimization
23	│ → -O0 -g (slowest, all vars visible)
24	├── Debuggable, some optimization (recommended for most dev work)
25	│ → -Og -g (-Og keeps debug experience good)
26	├── Release build with debug info (shipped, debuggable crashes)
27	│ → -O2 -g -gsplit-dwarf (or -O2 -g1 for lighter info)
28	└── Full release (no debug symbols)
29	→ -O2 -DNDEBUG
30	```
31
32	`-Og`: GCC's "debug-friendly optimization" — enables optimizations that don't interfere with debugging. Variables stay in registers where GDB can see them. Line numbers stay accurate. Best balance for development.
33
34	```bash
35	# GCC / Clang
36	gcc -Og -g -Wall main.c -o prog
37
38	# CMake build types
39	cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug # -O0 -g
40	cmake -S . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo # -O2 -g -DNDEBUG
41	cmake -S . -B build -DCMAKE_BUILD_TYPE=Release # -O2 -DNDEBUG
42	```
43
44	### 2. "Value optimized out" — causes and workarounds
45
46	```text
47	(gdb) print my_variable
48	$1 = <optimized out>
49	```
50
51	This means the compiler decided the variable's value doesn't need to be stored at this point — it might be:
52	- Kept only in a register (not the one GDB is looking at)
53	- Folded into a constant by constant propagation
54	- Eliminated because it's not used after this point
55	- Replaced by a later optimized value
56
57	Workarounds:
58
59	```c
60	// 1. Mark variable volatile (prevents optimization away)
61	volatile int counter = 0;
62	// Use sparingly — changes semantics
63
64	// 2. Use GCC attribute
65	int counter __attribute__((used)) = 0;
66
67	// 3. Compile problematic TU at lower optimization
68	// In CMake:
69	set_source_files_properties(tricky.c PROPERTIES COMPILE_FLAGS "-O0")
70
71	// 4. Use -Og instead of -O2 for the whole build
72
73	// 5. Look at register values directly
74	// (gdb) info registers
75	// (gdb) p/x $rax # value may be in a register
76	```
77
78	### 3. Reading inlined frames in GDB
79
80	With optimization, frequently-called small functions get inlined. GDB shows these as extra frames:
81
82	```text
83	(gdb) bt
84	#0 process_packet (data=0x7ff..., len=<optimized out>)
85	at network.c:45
86	#1 0x0000... in dispatch_handler (pkt=0x7ff...)
87	at handler.c:102
88	#2 (inlined by) event_loop () at main.c:78
89	#3 0x0000... in main () at main.c:200
90
91	# (inlined by) frames are virtual — they show the call chain
92	# that was inlined into the actual frame above
93	```
94
95	```bash
96	# Navigate inlined frames
97	(gdb) frame 2 # jump to the inlined frame
98	(gdb) up # move up through frames (including inlined)
99	(gdb) down # move down
100
101	# Show all frames including inlined
102	(gdb) backtrace full
103
104	# Set breakpoint inside inlined function
105	(gdb) break network.c:45 # may hit multiple inlined call sites
106	(gdb) break process_packet # hits all inline expansions
107	```
108
109	### 4. Line number discrepancies
110
111	Optimizers reorder instructions, so the "current line" in GDB may jump around:
112
113	```bash
114	# See which instructions map to which source lines
115	(gdb) disassemble /s function_name # interleaved source and asm
116
117	# Step by machine instruction (more accurate in optimized code)
118	(gdb) si # stepi — one machine instruction
119	(gdb) ni # nexti — one machine instruction (no step into)
120
121	# Show mixed source/asm at current point
122	(gdb) layout split # TUI mode: source + asm side by side
123	(gdb) set disassemble-next-line on
124
125	# Jump to specific address (when line stepping is unreliable)
126	(gdb) jump *0x400a2c
127	```
128
129	### 5. GDB scheduler-locking for optimized multithreaded code
130
131	With optimization, threads may race in unexpected ways when stepping:
132
133	```bash
134	# Lock the scheduler — only the current thread runs while stepping
135	(gdb) set scheduler-locking on
136
137	# Modes:
138	# off — all threads run freely (default)
139	# on — only current thread runs while stepping
140	# step — only

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