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RE: [avr-gcc-list] Order of variables placed in .data and .bss sections

From: Weddington, Eric
Subject: RE: [avr-gcc-list] Order of variables placed in .data and .bss sections
Date: Tue, 20 May 2008 12:06:25 -0600


> -----Original Message-----
> From: 
> address@hidden 
> [mailto:address@hidden
> org] On Behalf Of Raj Sharma
> Sent: Tuesday, May 20, 2008 11:21 AM
> To: address@hidden
> Subject: [avr-gcc-list] Order of variables placed in .data 
> and .bss sections
> Dear all,
> Is there a way to force some order in the way variables 
> (global/static) are placed in .data and .bss sections ? For 
> example, let my program has 2 initialized global variables g1 
> and g2 and 5 uninitialized global variables u1,u2,u3,u4 and 
> u5. g1 and g2 are first placed in program memory after .text 
> section and __do_copy_data copies them to the starting 
> address in SRAM. u1 through u5 are not explictitly stored in 
> program memory but __do_copy_bss places them just after g1 
> and g2 in SRAM and zeroes them out. I want to know if I can 
> somehow specify the order of these variables, say  g1 
> followed by g2; then u3,u4,u5,u1,u2. 
> I noticed that the order in which the variables are 
> declared/defined in C file or assembly file does not 
> correspond to the way they are placed in SRAM.
> Thanks in advance,
> Raj

Hello Raj,

In theory it can be done, but you will have to use -fdata-sections, and
a customized linker script. You may also have to either, customize the
startup code in avr-libc, or have some custom code right after startup
that takes care of the .data initialization and .bss clearing yourself.

Why do you need to do this anyway?

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