linkers-lto

使用方法

复制安装命令，在自己的智能体环境安装前先检查源码包。
从原始文档核对所需工具、凭据和支持的宿主。
说明输入材料与期望交付物，并对照来源检查输出。

npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill linkers-lto

开始前需了解

安装不包含模型订阅、API 额度或访问文件的权限。
仓库星数和安装量反映活跃情况，不等于独立质量或安全测试。

仓库原始内容

按源仓库内容呈现，保留标题、案例、代码、表格、链接以及原文引用的演示图片。

Linkers and LTO

Purpose

Guide agents through linker selection, common linker flags, link-order issues, LTO setup, and symbol-visibility management.

Triggers

"I'm getting undefined reference at link time"
"How do I enable LTO for a real project?"
"Which linker should I use: ld, gold, or lld?"
"How do I reduce binary size with --gc-sections?"
"How do I write or understand a linker script?"
"I have duplicate symbol or weak symbol issues"

Workflow

1. Linker selection

Linker	Invocation	Strengths
GNU ld (BFD)	default on Linux	Universal, stable
gold	`-fuse-ld=gold`	Faster than ld for C++; supports LTO plugins
lld (LLVM)	`-fuse-ld=lld`	Fastest, parallel, required for Clang LTO

bash

# Use lld with GCC or Clang
gcc -fuse-ld=lld -o prog ...
clang -fuse-ld=lld -o prog ...

# Check which linker is used
gcc -v -o prog main.c 2>&1 | grep 'Invoking'

2. Essential linker flags

bash

# Pass linker flags via compiler driver:
# -Wl,flag1,flag2   (comma-separated, no spaces)
# -Wl,flag1 -Wl,flag2  (separate -Wl options)

gcc main.c -o prog \
  -Wl,-rpath,/opt/mylibs/lib \     # runtime library search path
  -Wl,--as-needed \                 # only link libraries that are actually used
  -Wl,--gc-sections \               # remove unused sections (requires -ffunction-sections -fdata-sections)
  -Wl,-z,relro \                    # mark relocations read-only after startup
  -Wl,-z,now \                      # resolve all symbols at startup (full RELRO)
  -L/opt/mylibs/lib -lfoo

3. Link order matters (GNU ld)

GNU ld processes archives left-to-right. A library must come after the objects that need it.

bash

# Wrong: libfoo provides symbols needed by main.o
gcc main.o -lfoo libdep.a -o prog   # can fail if libdep.a needs libfoo

# Correct: dependencies after dependents
gcc main.o -lfoo -ldep -o prog

# If there are circular deps between archives:
gcc main.o -Wl,--start-group -lfoo -lbar -Wl,--end-group -o prog
# --start-group/--end-group: repeat search until no new symbols resolved

4. LTO with GCC

bash

# Compile
gcc -O2 -flto -ffunction-sections -fdata-sections -c foo.c -o foo.o
gcc -O2 -flto -ffunction-sections -fdata-sections -c bar.c -o bar.o

# Link (must pass -flto again)
gcc -O2 -flto -Wl,--gc-sections foo.o bar.o -o prog

# Archives: must use gcc-ar / gcc-ranlib, not plain ar
gcc-ar rcs libfoo.a foo.o
gcc-ranlib libfoo.a

Parallel LTO:

bash

gcc -O2 -flto=auto foo.o bar.o -o prog   # uses jobserver
gcc -O2 -flto=4   foo.o bar.o -o prog    # 4 parallel jobs

5. LTO with Clang / lld

bash

# Full LTO
clang -O2 -flto -fuse-ld=lld foo.c bar.c -o prog

# ThinLTO (faster, nearly same quality)
clang -O2 -flto=thin -fuse-ld=lld foo.c bar.c -o prog

# LTO with cmake: set globally
set(CMAKE_INTERPROCEDURAL_OPTIMIZATION ON)   # enables -flto

ThinLTO caches work: subsequent builds that reuse unchanged modules are faster. Cache location: specify with -Wl,--thinlto-cache-dir=/tmp/thinlto-cache.

6. Dead-code stripping

bash

# Compile with per-function/per-data sections
gcc -O2 -ffunction-sections -fdata-sections -c foo.c -o foo.o

# Link with garbage collection
gcc -Wl,--gc-sections foo.o -o prog

# Verify what was removed
gcc -Wl,--gc-sections -Wl,--print-gc-sections foo.o -o prog 2>&1 | head -20

On macOS, the linker strips dead code by default (-dead_strip).

7. Symbol visibility

Controlling visibility reduces DSO size and enables better LTO:

bash

# Hide all symbols by default, export explicitly
gcc -fvisibility=hidden -O2 -shared -fPIC foo.c -o libfoo.so

# In source, mark exports:
__attribute__((visibility("default"))) int my_public_function(void);

Or use a version script:

text

# foo.ver
{
  global: my_public_function; my_other_public;
  local: *;
};

bash

gcc -Wl,--version-script=foo.ver -shared -fPIC -o libfoo.so foo.o

8. Common linker errors

Error	Cause	Fix
`undefined reference to 'foo'`	Missing library or wrong order	Add `-lfoo`; move after the object that needs it
`multiple definition of 'foo'`	Symbol defined in two TUs	Remove duplicate; use `static` or `extern`
`cannot find -lfoo`	Library not in search path	Add `-L/path/to/lib`; install dev package
`relocation truncated`	Address overflow in relocation	Use `-mcmodel=large`; restructure image
`version 'GLIBC_2.33' not found`	Binary needs newer glibc	Link statically or rebuild on older host
`circular reference`	Archives mutually depend	Use `--start-group`/`--end-group`

9. Linker map file

bash

# Generate a map file (shows symbol → section → file)
gcc -Wl,-Map=prog.map -o prog foo.o bar.o
less prog.map

Useful for debugging binary size and symbol placement.

For a comprehensive linker and LTO flags reference, see references/flags.md.

Related skills

Use skills/binaries/elf-inspection for examining the resulting binary
Use skills/compilers/gcc or skills/compilers/clang for compile-phase LTO flags
Use skills/binaries/binutils for ar, strip, objcopy

使用方法

开始前需了解

Linkers and LTO

Purpose

Triggers

Workflow

1. Linker selection

2. Essential linker flags

3. Link order matters (GNU ld)

4. LTO with GCC

5. LTO with Clang / lld

6. Dead-code stripping

7. Symbol visibility

8. Common linker errors

9. Linker map file

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linkers-lto

使用方法

开始前需了解

Linkers and LTO

Purpose

Triggers

Workflow

1. Linker selection

2. Essential linker flags

3. Link order matters (GNU ld)

4. LTO with GCC

5. LTO with Clang / lld

6. Dead-code stripping

7. Symbol visibility

8. Common linker errors

9. Linker map file

Related skills

按任务相关推荐

domain-modeling

setup-matt-pocock-skills

setup-pre-commit

ecc-guide

更多 Skills

core-dumps

custom-allocators

ebpf

flamegraphs