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code optimization with gcc

+1 vote
507 views

My current compiler settings are 

arm-none-eabi-gcc -Wall -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -fshort-double-mcpu=cortex-m4 -mthumb -Qn -Os -finstrument-functions -mlong-calls -c temp.c -o temp.o
so on for temp1, temp2... Etc

I am compiling multiple C files. and linker settings are

ld -r temp.o -o one.o
so on for temp1, temp2... Etc

I am linking multiple .O files. Also I am using linker script i.e link.txt (invoked externally as below)

ld -cref -Map map.txt -S -T link.txt -temp.o -lm -lc -lgcc
arm-none-eabi-gcc -Wall sample.o -O Firmware.abs

Now, At output I get .abs file of 140KB.

My Questions are
1. How to optimize (reduce size of .abs) by using compiler or linker specific options?
2. There are Number of NOT used global variables and Blank Function Calls in my C files (NO Dead Code!!!!). Is it possible to perform some link time optimization.
3. Please Elaborate as I am new to this, I have referred sites, gcc help and tried some "lto" options but NO reduction is size.
4. I also tried using -fdata-sections -ffunction-sections
But It has INCREASED my firmware.abs file size from KB to MB (yes it is MB!!!!) I also wondered WHY?
I am using codesourcery arm toolchain evaluation. It has gcc version 4.5.2

posted Aug 7, 2013 by Luv Kumar

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1 Answer

0 votes

when using -fdata-sections and -ffunction-sections you also need to use --gc-sections during linking.

answer Aug 7, 2013 by Kumar Mitrasen
I will take care for your valuable suggestions.  I tried already using --gc-sections during linking but no improvements. I really have same questions
1. How to optimize (reduce size of .abs) by using complier or linker specific options?
2. There is number of not used global variables and blank function calls in my C files (but no dead Code!).Is it possible to perform some link time optimization?
3. Please elaborate as I am new to this, I have referred sites, gcc help and tried some "lto" options but no reduction is size.
4. I also tried using -fdata-sections -ffunction-sections but it has increased my firmware.abs file size from KB to MB (yes it is MB!)I wondered WHY?
I am using codesourcery arm toolchain evaluation. It has gcc version 4.5.2
commented Aug 7, 2013 by anonymous
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