Understand the Cause of Firmware Size Increase
Unexpected increases in firmware size can often be caused by a variety of factors such as inefficient code, incorrect linker script, or new library inclusions. Start by identifying what might have changed recently in your project that could lead to an increase in the binary size.
Use Linker Map Files
A linker map file is an essential tool for understanding how your firmware is structured and where memory is being used. Enable the linker map file by adding the -Map option to your linker flags:
ld -o output.elf -Map=output.map ...
Review the .map file to see where size bloat may be happening. Look for large sections you didn't expect, extra padding, or unexpected symbols.
Analyze Code and Data Sections
Check the .text, .data, and .bss sections in the map file to understand what is consuming the most space.
- .text: Contains executable code. Look for large functions or inlined code that could be increasing size.
- .data: Contains initialized data. Consider optimizing data storage or compressing large static structures.
- .bss: Contains uninitialized data. High usage shows significant use of global or static variables.
Optimize Code for Size
Function Inlining: Excessive inlining increases size. Use the __attribute__((noinline)) attribute to prevent it.
Code Duplication: Check for duplication and consider factoring common code into functions.
Compiler Optimization: Use compiler optimization flags like -Os for size:
```bash
gcc -Os -o output.o input.c
```
Review Linker Script
Your linker script controls how sections are placed in memory. Ensure that your script aligns sections correctly to avoid bloating due to alignment gaps. Customizing your script can help manage how memory is used:
SECTIONS
{
. = 0x1000;
.text : { *(.text*) }
.data : { *(.data*) }
.bss : { *(.bss*) }
}
Make sure sections do not overlap unless intended and are properly aligned.
Reduce Library Footprint
Link only necessary parts of libraries or use minimal versions if available. Static linking entire libraries can pull in unwanted code. Use function-level linking with --gc-sections:
gcc -Wl,--gc-sections -o output.elf ...
Investigate Dependent Libraries
Use objdump to inspect binary object files:
objdump -d output.o
Check for excessive or unused library functions that may have been linked in inadvertently.
Enable LTO (Link Time Optimization)
Enabling LTO can significantly reduce binary size by optimizing across object files. Compile with -flto:
gcc -flto -c file1.c
gcc -flto -c file2.c
gcc -flto -o output.elf file1.o file2.o
Each of these strategies can help ensure that your firmware maintains an optimal and expected size. Remember that every piece of code has trade-offs, and balancing performance with size is key. Continue to iterate and test different approaches to attain the desired outcome.
