resource-optimization-lowend

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🇺🇸

Original

English

🇨🇳

Translation

Chinese

Resource Optimization (Low-End Systems)

资源优化（低端系统）

Purpose

目标

Guide agents through flash and RAM optimization on constrained devices: compiler size flags, linker map analysis, stack usage measurement, dead code elimination, and size-vs-speed tradeoffs — for bare-metal and small RTOS images.

指导 Agent 在资源受限设备上进行 flash 和 RAM 优化：编译器体积优化标志、linker map 分析、栈使用量测量、无用代码消除，以及体积与速度之间的权衡——适用于裸机和小型 RTOS 镜像。

When to Use

使用场景

Firmware exceeds flash budget
Stack overflow in production only
Choosing
```
-Os
```
vs
```
-O2
```
on MCU
Finding unexpected
```
.rodata
```
or
```
.bss
```
growth

固件超出 flash 预算
栈溢出仅在生产环境中发生
在 MCU 上选择
```
-Os
```
与
```
-O2
```
发现异常的
```
.rodata
```
或
```
.bss
```
增长

Workflow

工作流

1. Size measurement toolchain

1. 体积测量工具链

bash

arm-none-eabi-size -A firmware.elf
arm-none-eabi-objdump -h firmware.elf
nm --size-sort -S firmware.elf | tail -20

bash

arm-none-eabi-size -A firmware.elf
arm-none-eabi-objdump -h firmware.elf
nm --size-sort -S firmware.elf | tail -20

2. Linker map file

2. Linker map 文件

/* linker.ld */
OUTPUT_FORMAT("elf32-littlearm")
ENTRY(Reset_Handler)

SECTIONS
{
  /* ... */
}

/* Generate map */
/* gcc ... -Wl,-Map=firmware.map */

bash

grep -E '\.text|\.rodata|\.data|\.bss' firmware.map | head

Identify largest symbols and unexpected library pull-in.

/* linker.ld */
OUTPUT_FORMAT("elf32-littlearm")
ENTRY(Reset_Handler)

SECTIONS
{
  /* ... */
}

/* Generate map */
/* gcc ... -Wl,-Map=firmware.map */

bash

grep -E '\.text|\.rodata|\.data|\.bss' firmware.map | head

找出最大的符号和意外引入的库。

3. Compiler flags

3. 编译器标志

Flag	Effect
`-Os`	Size-first optimization
`-ffunction-sections -fdata-sections`	Per-symbol sections
`-Wl,--gc-sections`	Drop unused sections
`-flto`	Cross-TU dead code elimination
`-specs=nano.specs`	Smaller newlib (GCC ARM)

makefile

CFLAGS += -Os -ffunction-sections -fdata-sections
LDFLAGS += -Wl,--gc-sections -Wl,--print-memory-usage

标志	效果
`-Os`	优先优化体积
`-ffunction-sections -fdata-sections`	按符号划分段
`-Wl,--gc-sections`	丢弃未使用的段
`-flto`	跨 TU 消除无用代码
`-specs=nano.specs`	更小的 newlib（GCC ARM）

makefile

CFLAGS += -Os -ffunction-sections -fdata-sections
LDFLAGS += -Wl,--gc-sections -Wl,--print-memory-usage

4. Stack analysis

4. 栈分析

bash

undefined

bash

undefined

Static (if built with -fstack-usage)

find . -name '*.su' -exec cat {} ;

Linker stack symbol

grep _estack firmware.map


Runtime: fill stack with pattern (`0xDEADBEEF`), run tests, scan high-water mark. FreeRTOS: `uxTaskGetStackHighWaterMark`.

grep _estack firmware.map


运行时：使用模式（`0xDEADBEEF`）填充栈，运行测试并扫描 high-water mark。FreeRTOS：`uxTaskGetStackHighWaterMark`。

5. RAM categories

5. RAM 类别

Section	Tactic
`.bss`	Shrink buffers; pool allocators
`.data`	Move const to flash ( `const` → `.rodata` )
Heap	Avoid malloc; fixed pools
Stack	Reduce nesting; smaller ISR stacks

段	策略
`.bss`	缩小缓冲区；使用池分配器
`.data`	将 const 移至 flash（ `const` → `.rodata` ）
Heap	避免 malloc；使用固定内存池
Stack	减少嵌套；缩小 ISR 栈

6. Size vs speed decision

6. 体积与速度的决策

Hot path in ISR or 1 kHz loop?
├── Yes → -O2 for that file (#pragma GCC optimize)
└── No  → -Os globally

Hot path in ISR or 1 kHz loop?
├── Yes → -O2 for that file (#pragma GCC optimize)
└── No  → -Os globally

7. Agent usage

7. Agent 使用方式

/resource-optimization-lowend Find top 10 flash consumers in firmware.map and suggest -gc-sections fixes

/resource-optimization-lowend Find top 10 flash consumers in firmware.map and suggest -gc-sections fixes

Common Problems

常见问题

Symptom	Cause	Fix
printf pulls 20+ KB	Full newlib printf	`_write` retarget; tiny printf
`--gc-sections` broke IRQ	Section collected	`KEEP()` in linker script
Stack overflow late	Deep call + IRQ nest	Measure HW stack; increase `_estack`
RAM zero but big ELF	`.data` not loaded	Check VMA/LMA
LTO link fail	Mixed compiler versions	Same GCC for all objects

症状	原因	修复方案
printf 引入 20+ KB	完整的 newlib printf	重定向 `_write` ；使用 tiny printf
`--gc-sections` 导致 IRQ 失效	段被回收	在 linker script 中使用 `KEEP()`
栈在后期才溢出	调用层级过深 + IRQ 嵌套	测量硬件栈；增大 `_estack`
RAM 为零但 ELF 很大	`.data` 未加载	检查 VMA/LMA
LTO 链接失败	编译器版本混用	所有目标文件使用同一 GCC

resource-optimization-lowend

Original

Translation

Resource Optimization (Low-End Systems)

资源优化（低端系统）

Purpose

目标

When to Use

使用场景

Workflow

工作流

1. Size measurement toolchain

1. 体积测量工具链

2. Linker map file

2. Linker map 文件

3. Compiler flags

3. 编译器标志

4. Stack analysis

4. 栈分析

Static (if built with -fstack-usage)

Static (if built with -fstack-usage)

Linker stack symbol

Linker stack symbol

5. RAM categories

5. RAM 类别

6. Size vs speed decision

6. 体积与速度的决策

7. Agent usage

7. Agent 使用方式

Common Problems

常见问题

Related Skills

相关 Skill