[LLVMdev] LLD improvement plan

[Will Newton]

On Wed, May 6, 2015 at 5:30 PM, Daniel Dilts <diltsman at gmail.com> wrote:
>
>
> On Wed, May 6, 2015 at 12:51 AM, Will Newton <will.newton at gmail.com> wrote:
>>
>> On Wed, May 6, 2015 at 6:22 AM, Chris Lattner <clattner at apple.com> wrote:
>> > On May 5, 2015, at 6:47 PM, Daniel Dilts <diltsman at gmail.com> wrote:
>> >
>> > Take a look at how debuggers have migrated through the years.  They too
>> >>
>> >> used to have their own script format.  Now most (all?) popular
>> >> debuggers
>> >> do scripting through embedding an actual programming language.  This
>> >> could be a better way forward for linkers as well -- embed Python in
>> >> the
>> >> linker, define a Python API for linkable item placement, entry point,
>> >> symbol operations, etc..., and then you also have the rest of Python at
>> >> your fingertips.
>> >
>> >
>> > I mostly care about specifying address where specific symbols will be
>> > placed
>> > and specifying the memory layout of the platform.   I normally use
>> > __attribute__((section(""))) to place the symbols in their own sections
>> > and
>> > then use the linker script to place the sections at the required
>> > addresses.
>> > How would this be accomplished without linker scripts?
>> >
>> >
>> > I’d prefer to use an "__attribute__((address(0x1234)))” myself.  That
>> > way
>> > you can control platform specifics with #ifdefs.
>>
>> But that way you have to do layout by hand in C. Generally you won't
>> know the size of the preceding code or data so you won't know what
>> address to put things at at the granularity of a single C level
>> object/function. Better to say "put this in the ROM section" and set
>> the address of the ROM section once in a linker script and let the
>> linker do the layout.
>
>
> The real use case is on platforms, like ARM, where control registers are
> mapped to a specific address range.  Then it is useful to put an object that
> deals with the control registers at a specific address.
> __attribute__((address(0x1234))) can be replaced with a platform specific
> linker script.  Which is better?  I don't know, I haven't spent any time
> comparing them.

Why would you want to put an object at the address of some registers?
You would just want a cast would you not?

e.g. regs = (struct MyRegBlock *)0x1234