AW: Constant at fixed address

[<stefan@franke.ms>]

> -----Ursprüngliche Nachricht-----
> Von: Gcc-help <gcc-help-bounces+bebbo=bejy.net@gcc.gnu.org> Im
> Auftrag von David Brown
> Gesendet: Freitag, 25. Februar 2022 18:57
> An: Martin Sebor <msebor@gmail.com>; Henrique Coser
> <henrique.coser@tex.com.br>; gcc-help@gcc.gnu.org
> Betreff: Re: Constant at fixed address
> 
> On 25/02/2022 17:45, Martin Sebor via Gcc-help wrote:
> > On 2/25/22 09:01, Henrique Coser wrote:
> >> Hello,
> >>
> >> I need a help. I'm trying to solve a problem for weeks.
> >> I have a embeded software that is a boot loader. It puts the boot
> >> load version at a specific address.
> >> My memmory starts at 0x400000 with 0x1400 size. My constant version
> >> string value must be placed @0x401000 with 8bytes length.
> >> If I place this const value into a section like this:
> >>
> >>   const unsigned char Version[8] __attribute__ ((section
> >> (".bootversion")))  = "V1.0.1a";
> >>
> >> I got this error:
> >>
> >> section .bootversion LMA [00401000,00401007] overlaps section .text
> >> LMA [00400000,00401013]collect2.exe(0,0): error: ld returned 1 exit
> >> status
> >>
> >> I have already tried to split flash memmory using linker script but
> >> it does not worked.
> >> I wish to find something like "automatic" split.
> >>
> >> For example, this code was compiled using ARM Keil. With ARM Keil I
> >> have the attribute that makes all the magic :
> >>   const unsigned char Version[8] __attribute__((at(0x0401000))) =
> >> "V1.0.1a";
> >>
> >> I dont know if is possible to have something as pratical as ARM Keil
> >> attribute in GCC.
> >
> > GCC for the AVR target supports a couple of attributes that can be
> > used to pin a variable declaration to a fixed address: address and io.
> > It doesn't look to me like they're put in their own sections like in
> > the ARM Keil compiler (but the section attribute can be used for
> > that).
> >
> > Beside your use case, exposing at least the address attribute in all
> > targets would make would also solve a long-standing problem with GCC
> > issuing warnings for accesses to hardwired addresses).
> >
> > I suggest opening an enhancement request in Bugzilla.
> >
> > Martin
> >
> >
> 
> I second that request - it would definitely be convenient to be able to put a
> variable or section at a specific address without having to modify a linker
> script.  This is a feature that most embedded toolchains (Keil, IAR, etc.)
> support.
> 
> Note that the attributes for the AVR here don't do what is needed, as far as I
> can see - it looks like they declare the variable at the given address, but that
> does not mean that there will be an absolute section allocated in the link.  In
> other words, using the AVR "address"
> attribute to put "Version" at address 0x0401000 will not actually put the
> initialised data there, nor will it prevent the address being used by anything
> else that is linked to that memory area.
> 
> The example for the "address" attribute is :
> 
> 	volatile int porta __attribute__((address (0x600)));
> 
> The effect of this is very similar to the more common and portable version
> used for other targets:
> 
> 	#define porta *((volatile int *) 0x600)
> 
> Henrique needs more than that here.
> 
> AFAIK, Henrique, the only way to achieve your needs are a modified linker
> script.  It's not hard to do that, but of course it looks hard the first time you
> do it!  Post a copy of your current linker script and I can try to give you ideas
> for modification.
> 
> 

Isn't this already possible by using a section:

   volatile int porta __attribute__((__section("section_600")));

and using an appropriate linker script?

SECTIONS
{
  .section_600 0x600: {
   *(.section_600)
...


Stefan