llvm dev - Apr 2010 - [LLVMdev] Defining a pointer to a specific memory address?

I've been working through the getting started and language reference docs.
One thing that's not immediately clear if it's possible is to define a
global pointer to a specific memory address.

I'm looking at ways to use LLVM to target a small ARM embedded processor,
and there are a great many hardware registers mapped into the address space. I
tried making a little sample C program to see how llvm-gcc generated the access,
and it used this:

  volatile store i32 -1430532899, i32* inttoptr (i64 4294963200 to i32*), align
4

for this C code:

typedef volatile unsigned int AT91_REG;// Hardware register definition
#define AT91_CAST(a) (a)
#define AT91C_BASE_SYS       (AT91_CAST(AT91_REG*) 	0xFFFFF000) // (SYS) Base
Address

void
main()
{
	*AT91C_BASE_SYS = 0xaabbccdd;
}


Is there any way to do the equivalent with a global?

Thanks,
Rick

Try compiling the following C code:

typedef volatile unsigned int AT91_REG;// Hardware register definition
#define AT91_CAST(a) (a)
#define AT91C_BASE_SYS       (AT91_CAST(AT91_REG*)      0xFFFFF000) //
(SYS) Base Address

AT91_REG* global = AT91C_BASE_SYS;



On Fri, Apr 9, 2010 at 9:17 PM, Rick Mann <rmann at latencyzero.com>
wrote:
> I've been working through the getting started and language reference
docs. One thing that's not immediately clear if it's possible is to
define a global pointer to a specific memory address.
>
> I'm looking at ways to use LLVM to target a small ARM embedded
processor, and there are a great many hardware registers mapped into the address
space. I tried making a little sample C program to see how llvm-gcc generated
the access, and it used this:
>
>  volatile store i32 -1430532899, i32* inttoptr (i64 4294963200 to i32*),
align 4
>
> for this C code:
>
> typedef volatile unsigned int AT91_REG;// Hardware register definition
> #define AT91_CAST(a) (a)
> #define AT91C_BASE_SYS       (AT91_CAST(AT91_REG*)      0xFFFFF000) //
(SYS) Base Address
>
> void
> main()
> {
>        *AT91C_BASE_SYS = 0xaabbccdd;
> }
>
>
> Is there any way to do the equivalent with a global?
>
> Thanks,
> Rick
>
>
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