Hi Andrii,
On 14/11/2019 11:31, Andrii Anisov wrote:
On 13.11.19 07:50, Julien Grall wrote:
To be honest, I don't think this file should even exist. This looks
like a copy of xen.lds.S with a different syntax.
And lacking features like symbols definition, current address setup, etc.
That's fine, you can introduce macro that will just be a NOP for
armlinker and implemented for ld.
Furthermore, the comments from Stefano shows that is going to be hard
to maintain/check everything has been written correctly.
It will be terribly hard.
So how about trying to abstract xen.lds.S?
I failed to find the common ground for them.
You are very welcomed to suggest that piece of code.
I don't have time to work on the full feature, but I can provide a few
ideas so you can implement it.
If we look at the .text section. For the GNU linker script, it is:
_start = .;
.text : {
_stext = .; /* Text section */
*(.text)
*(.text.cold)
*(.text.unlikely)
*(.fixup)
*(.gnu.warning)
_etext = .; /* End of text section */
} :text = 0x9090
For armds, you implement as
;_start
;_stext
_text AlignExpr(+0, PAGE_SIZE) PADVALUE 0x9090
{
*(.text*)
*(.text.cold)
*(.text.unlikely)
*(.fixup)
*(.gnu.warning)
}
;_etext
You could imagine the following abstraction:
SYMBOL(_start)
SECTION(_text)
SYMBOL(_stext)
*(.text)
*(.text.cold)
*(.text.unlikely)
*(.fixup)
*(.gnu.warning)
SYMBOL(_etext)
ESECTION(text)
For GNU linker scripts, the macros would be implemented as
#define SYMBOL(sym) sym := .;
#define SECTION(sect) sect : {
#define ESECTION(phdr) } :phdr = 0x9090
For the Arm scatter file, the macros would be implemented as
/* Symbols are not declared in the scatter file */
#define SYMBOL(sym) ;sym
#define SECTION(sect) sect AlignExpr(+0, PAGE_SIZE) PADVALUE 0x9090 {
#define ESECTION(phdr) }
A few caveats:
- I am not entirely sure why we specific the pading value only for
.text and not the other. I also don't understand the 0x9090 value.
Stefano? It may be possible to remove this completely.
- The alignment could be passed as a parameter for the macro
- The linker script may need some reshuffle in order to make it generic.
On a side note, I noticed that you are using *(.text*), rather than
*(.text). Could you explain why?
> +/*
> + * armlink does not understand shifts in scat file expressions
> + * so hardcode needed values
> + */
Please give a pointer to the doc of the armlink in the commit message.
So we can easily cross-check what's happening.
The best cross-check would be running the compiler. Yet, this particular
thing is somehow documented [1].
In this case, I don't particularly like the re-definition of the
defines outside of their header. This is going to make more difficult
if we have to update them in the future.
I can see a few ways to do it:
- Avoid using shifts in the definitions
- Find a way to evaluate the value (maybe similar to asn-offset)
before using them.
My preference would be the latter but I could be convinced for the
former.
The first option is not realistic. I suggested ARM to consider shifts
support as an improvement for their compiler.
I'd be very happy to adopt the second option. Do you have any code
examples or hints how to evaluate expressions on the pre-processing stage?
I wasn't thinking to do it a pre-processing state but rather generating
an header that will have the value already computed.
Have a look at how we generate defininition for assembly (see
arch/arm32/asm-offsets.c).
Looking at the link you provided, I noticed that * is supported by the
scatter file. So it might be possible to introduce a macro LSHIFT(a, b)
that will be implemented as a << b or (a * a * a ...) depending on the
users. The major difficulty here would be to find a way to generate a *
a * a... nicely during pre-processing.
Cheers,
--
Julien Grall
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