Re: to reduce footprint

[Lin George <george4academic at yahoo dot com>]

Thanks John! I want to reduce the file size of my shared library. I think you are an expert in this field. I have read through your comments below and I am especially interested in the following points,

1. Use footprint techniques (such as inheritance, specialization and partial
specialization) to reduce the amount of code generated by templates.

Could you provide some references to them?

2. Avoid the convenience of multiple copies of weak linkage for stronger,
explicit linkage.  [Depending on what kind of footprint you are trying to
reduce.]

Could you provide some reference about weak linker and a strong (explicit linker)?

3. Make sure all your header files do not emit any code (e.g., no static
variables in header files).  Compile your header files to confirm that all
your header files are non-code-generating.

I can understand what you mean, but I do not know why if header files emit code, the footprint will be larger?

4. --gc-sections -ffunction-sections -fdata-sections

gcc manual does not contain much information about these parameters. Could you briefly introduce the functions of them?


thanks in advance,
George


----- Original Message ----
From: John Love-Jensen <eljay@adobe.com>
To: Lin George <george4academic@yahoo.com>; MSX to GCC <gcc-help@gcc.gnu.org>
Sent: Tuesday, December 19, 2006 9:18:32 PM
Subject: Re: to reduce footprint


Hi George,

> I am wondering how to reduce the footprint of a binary build (C/C++) program
> generated by gcc.

Memory footprint, or file footprint?

> 1. Any ideas of reduce the footprint of a debug version build?
> 2. Any ideas of reduce the footprint of a release version build?

Just some suggestions, by no means a comprehensive list...

If you have an object file with 100 routines in it, but you only use 1
routine out of the hundred, isolate that one routine and link just it (.o
file).  Then you won't get the unnecessary 99 fallow routines.

Use footprint techniques (such as inheritance, specialization and partial
specialization) to reduce the amount of code generated by templates.

Avoid the convenience of multiple copies of weak linkage for stronger,
explicit linkage.  [Depending on what kind of footprint you are trying to
reduce.]

Make sure all your header files do not emit any code (e.g., no static
variables in header files).  Compile your header files to confirm that all
your header files are non-code-generating.

Use code coverage tools to identify code that is not used.  Figure out why
it isn't used, and consider if it can be disposed.

Use enums instead of strings for references to resources.

If you have a value range of, say, 0 to 100, and you have a large array of
them, consider using a typedef unsigned char uint8_t; instead of an array of
int to hold them.

> I think some linker or compiler options may help, what are they? Any other
> ideas to reduce footprint?

Depending on your platform, you may be able to use these switches:
--gc-sections -ffunction-sections -fdata-sections

hHTH,
--Eljay

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