gcc

Name: gcc
Author: mohitmishra786

359installs19forks

How to install gcc?

mohitmishra786/low-level-dev-skills/gcc

$npx -y skills add mohitmishra786/low-level-dev-skills --skill gcc

Installs into the current project.

Summary

GCC compiler skill for C/C++ projects. Use when selecting optimization levels, warning flags, debug builds, LTO, sanitizer instrumentation, or diagnosing compilation errors with GCC. Covers flag selection for debug vs release, ABI concerns, preprocessor macros, profile-guided opt

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SKILL.md

1	# GCC
2
3	## Purpose
4
5	Guide agents through GCC invocation: flag selection, build modes, warning triage, PGO, LTO, and common error patterns. Assume the project uses GNU Make, CMake, or a shell script.
6
7	## Triggers
8
9	- "What flags should I use for a release build?"
10	- "GCC is giving me a warning/error I don't understand"
11	- "How do I enable LTO / PGO with GCC?"
12	- "How do I compile with `-fsanitize`?"
13	- "My binary is too large / too slow"
14	- Undefined reference errors, ABI mismatch, missing symbols
15
16	## Workflow
17
18	### 1. Choose a build mode
19
20	\| Goal \| Recommended flags \|
21	\|------\|-------------------\|
22	\| Debug \| `-g -O0 -Wall -Wextra` \|
23	\| Debug + debuggable optimisation \| `-g -Og -Wall -Wextra` \|
24	\| Release \| `-O2 -DNDEBUG -Wall` \|
25	\| Release (max perf, native only) \| `-O3 -march=native -DNDEBUG` \|
26	\| Release (min size) \| `-Os -DNDEBUG` \|
27	\| Sanitizer (dev) \| `-g -O1 -fsanitize=address,undefined` \|
28
29	Always pass `-std=c11` / `-std=c++17` (or the required standard) explicitly. Never rely on the implicit default.
30
31	### 2. Warning discipline
32
33	Start with `-Wall -Wextra`. For stricter standards compliance add `-Wpedantic`. To treat all warnings as errors in CI: `-Werror`.
34
35	Suppress a specific warning only in a narrow scope:
36
37	```c
38	#pragma GCC diagnostic push
39	#pragma GCC diagnostic ignored "-Wunused-parameter"
40	// ...
41	#pragma GCC diagnostic pop
42	```
43
44	Do not pass `-w` (silences everything) except as a last resort for third-party headers.
45
46	### 3. Debug information
47
48	- `-g` — DWARF debug info, default level 2
49	- `-g3` — includes macro definitions (useful with GDB `macro expand`)
50	- `-ggdb` — DWARF extensions optimal for GDB
51	- `-gsplit-dwarf` — splits `.dwo` files; reduces link time, needed for `debuginfod`
52
53	Pair `-g` with `-Og` (not `-O0`) when you need readable optimised code in GDB.
54
55	### 4. Optimisation decision tree
56
57	```text
58	Need max throughput on a fixed machine?
59	yes -> -O3 -march=native -flto
60	no -> profiling available?
61	yes -> -O2 -fprofile-use
62	no -> -O2
63	Size-constrained (embedded, shared lib)?
64	yes -> -Os (or -Oz with clang)
65	```
66
67	`-O3` vs `-O2`: `-O3` adds aggressive loop transformations (`-funswitch-loops`, `-fpeel-loops`, `-floop-interchange`) and more aggressive inlining. Use `-O3` only after benchmarking; it occasionally regresses due to i-cache pressure.
68
69	`-Ofast`: enables `-ffast-math` which breaks IEEE 754 semantics (NaN handling, associativity). Avoid unless the numerical domain explicitly permits it.
70
71	### 5. Link-time optimisation (LTO)
72
73	```bash
74	# Compile
75	gcc -O2 -flto -c foo.c -o foo.o
76	gcc -O2 -flto -c bar.c -o bar.o
77	# Link (must pass -flto again)
78	gcc -O2 -flto foo.o bar.o -o prog
79	```
80
81	Use `gcc-ar` / `gcc-ranlib` instead of `ar` / `ranlib` when archiving LTO objects into static libs.
82
83	For parallel LTO: `-flto=auto` (uses `make`-style jobserver) or `-flto=N`.
84
85	See [references/flags.md](references/flags.md) for full flag reference. See `skills/binaries/linkers-lto` for linker-level LTO configuration.
86
87	### 6. Profile-guided optimisation (PGO)
88
89	```bash
90	# Step 1: instrument
91	gcc -O2 -fprofile-generate prog.c -o prog_inst
92	# Step 2: run with representative workload
93	./prog_inst < workload.input
94	# Step 3: optimise with profile
95	gcc -O2 -fprofile-use -fprofile-correction prog.c -o prog
96	```
97
98	`-fprofile-correction` handles profile data inconsistencies from multi-threaded runs.
99
100	### 7. Preprocessor and standards
101
102	- Inspect macro expansion: `gcc -E file.c \| less`
103	- Dump predefined macros: `gcc -dM -E - < /dev/null`
104	- Force strict standard: `-std=c11 -pedantic-errors`
105	- Disable GNU extensions: `-std=c11` (not `-std=gnu11`)
106
107	### 8. Common error triage
108
109	\| Symptom \| Likely cause \| Fix \|
110	\|---------\|-------------\|-----\|
111	\| `undefined reference to 'foo'` \| Missing `-lfoo` or wrong link order \| Add `-lfoo`; move `-l` flags after object files \|
112	\| `multiple definition of 'x'` \| Variable defined (not just declared) in a header \| Add `extern` in header, define in one `.c` \|
113	\| `implicit declaration of function` \| Missing `#include` \| Add the header \|
114	\| `warning: incompatible pointer types` \| Wrong cast or missing prototype \| Fix the type; check headers \|
115	\| ABI errors with C++ \| Mixed `-std=` or different `libstdc++` \| Unify `-std=` across all TUs \|
116	\| `relocation truncated` \| Overflow on a 32-bit relative relocation \| Use `-mcmodel=large` or restructure code \|
117
118	For sanitizer reports, use `skills/runtimes/sanitizers`.
119
120	### 9. Useful one-liners
121
122	```bash
123	# Show all flags enabled at -O2
124	gcc -Q --help=optimizers -O2 \| grep enabled
125
126	# Preprocess only (che

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Type

gcc

359installs19forks

View on GitHub

How to install gcc?

mohitmishra786/low-level-dev-skills/gcc

$npx -y skills add mohitmishra786/low-level-dev-skills --skill gcc

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# GCC
2
3	## Purpose
4
5	Guide agents through GCC invocation: flag selection, build modes, warning triage, PGO, LTO, and common error patterns. Assume the project uses GNU Make, CMake, or a shell script.
6
7	## Triggers
8
9	- "What flags should I use for a release build?"
10	- "GCC is giving me a warning/error I don't understand"
11	- "How do I enable LTO / PGO with GCC?"
12	- "How do I compile with `-fsanitize`?"
13	- "My binary is too large / too slow"
14	- Undefined reference errors, ABI mismatch, missing symbols
15
16	## Workflow
17
18	### 1. Choose a build mode
19
20	\| Goal \| Recommended flags \|
21	\|------\|-------------------\|
22	\| Debug \| `-g -O0 -Wall -Wextra` \|
23	\| Debug + debuggable optimisation \| `-g -Og -Wall -Wextra` \|
24	\| Release \| `-O2 -DNDEBUG -Wall` \|
25	\| Release (max perf, native only) \| `-O3 -march=native -DNDEBUG` \|
26	\| Release (min size) \| `-Os -DNDEBUG` \|
27	\| Sanitizer (dev) \| `-g -O1 -fsanitize=address,undefined` \|
28
29	Always pass `-std=c11` / `-std=c++17` (or the required standard) explicitly. Never rely on the implicit default.
30
31	### 2. Warning discipline
32
33	Start with `-Wall -Wextra`. For stricter standards compliance add `-Wpedantic`. To treat all warnings as errors in CI: `-Werror`.
34
35	Suppress a specific warning only in a narrow scope:
36
37	```c
38	#pragma GCC diagnostic push
39	#pragma GCC diagnostic ignored "-Wunused-parameter"
40	// ...
41	#pragma GCC diagnostic pop
42	```
43
44	Do not pass `-w` (silences everything) except as a last resort for third-party headers.
45
46	### 3. Debug information
47
48	- `-g` — DWARF debug info, default level 2
49	- `-g3` — includes macro definitions (useful with GDB `macro expand`)
50	- `-ggdb` — DWARF extensions optimal for GDB
51	- `-gsplit-dwarf` — splits `.dwo` files; reduces link time, needed for `debuginfod`
52
53	Pair `-g` with `-Og` (not `-O0`) when you need readable optimised code in GDB.
54
55	### 4. Optimisation decision tree
56
57	```text
58	Need max throughput on a fixed machine?
59	yes -> -O3 -march=native -flto
60	no -> profiling available?
61	yes -> -O2 -fprofile-use
62	no -> -O2
63	Size-constrained (embedded, shared lib)?
64	yes -> -Os (or -Oz with clang)
65	```
66
67	`-O3` vs `-O2`: `-O3` adds aggressive loop transformations (`-funswitch-loops`, `-fpeel-loops`, `-floop-interchange`) and more aggressive inlining. Use `-O3` only after benchmarking; it occasionally regresses due to i-cache pressure.
68
69	`-Ofast`: enables `-ffast-math` which breaks IEEE 754 semantics (NaN handling, associativity). Avoid unless the numerical domain explicitly permits it.
70
71	### 5. Link-time optimisation (LTO)
72
73	```bash
74	# Compile
75	gcc -O2 -flto -c foo.c -o foo.o
76	gcc -O2 -flto -c bar.c -o bar.o
77	# Link (must pass -flto again)
78	gcc -O2 -flto foo.o bar.o -o prog
79	```
80
81	Use `gcc-ar` / `gcc-ranlib` instead of `ar` / `ranlib` when archiving LTO objects into static libs.
82
83	For parallel LTO: `-flto=auto` (uses `make`-style jobserver) or `-flto=N`.
84
85	See [references/flags.md](references/flags.md) for full flag reference. See `skills/binaries/linkers-lto` for linker-level LTO configuration.
86
87	### 6. Profile-guided optimisation (PGO)
88
89	```bash
90	# Step 1: instrument
91	gcc -O2 -fprofile-generate prog.c -o prog_inst
92	# Step 2: run with representative workload
93	./prog_inst < workload.input
94	# Step 3: optimise with profile
95	gcc -O2 -fprofile-use -fprofile-correction prog.c -o prog
96	```
97
98	`-fprofile-correction` handles profile data inconsistencies from multi-threaded runs.
99
100	### 7. Preprocessor and standards
101
102	- Inspect macro expansion: `gcc -E file.c \| less`
103	- Dump predefined macros: `gcc -dM -E - < /dev/null`
104	- Force strict standard: `-std=c11 -pedantic-errors`
105	- Disable GNU extensions: `-std=c11` (not `-std=gnu11`)
106
107	### 8. Common error triage
108
109	\| Symptom \| Likely cause \| Fix \|
110	\|---------\|-------------\|-----\|
111	\| `undefined reference to 'foo'` \| Missing `-lfoo` or wrong link order \| Add `-lfoo`; move `-l` flags after object files \|
112	\| `multiple definition of 'x'` \| Variable defined (not just declared) in a header \| Add `extern` in header, define in one `.c` \|
113	\| `implicit declaration of function` \| Missing `#include` \| Add the header \|
114	\| `warning: incompatible pointer types` \| Wrong cast or missing prototype \| Fix the type; check headers \|
115	\| ABI errors with C++ \| Mixed `-std=` or different `libstdc++` \| Unify `-std=` across all TUs \|
116	\| `relocation truncated` \| Overflow on a 32-bit relative relocation \| Use `-mcmodel=large` or restructure code \|
117
118	For sanitizer reports, use `skills/runtimes/sanitizers`.
119
120	### 9. Useful one-liners
121
122	```bash
123	# Show all flags enabled at -O2
124	gcc -Q --help=optimizers -O2 \| grep enabled
125
126	# Preprocess only (che

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