AW: code optimization.

Christoph Kobe Christoph.Kobe@ek-team.de
Wed Aug 7 07:16:00 GMT 2013


-----Ursprüngliche Nachricht-----
Von: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org] Im Auftrag von hemant undale
Gesendet: Mittwoch, 7. August 2013 08:04
An: gcc-help@gcc.gnu.org
Betreff: code optimization.

Hi to All,
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 complier 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 

Thanks for patiently reading my question.

----

Hi hemantu,

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

Also, people might find it easier to read your email carefully
(and you will get more quality responses) if you invest some more
time into formatting your text (paragrahs, less exclamation marks
& question marks, no capitals). As a good starting point, a google
search for "mailing list etiquette" points here:
http://www.freebsd.org/doc/en/articles/mailing-list-faq/etiquette.html

Regards
Christoph



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