Hi James,
On Sat, 2023-08-26 at 09:53 +0100, James Le Cuirot wrote:
> Once that is agreed, I'm happy to put together the patch to automatically
> enable the flag for this tuple in GCC. The part I do need help with is
> necessary changes to glibc, if any. Assembly is not my area at all, so what I
> came up with here was a total guess.
>
>
> --- a/sysdeps/m68k/crti.S 2022-07-29 23:03:09.000000000 +0100
> +++ b/sysdeps/m68k/crti.S 2022-11-30 21:41:52.710135230 +0000
> @@ -56,7 +56,7 @@
> #endif
>
> .section .init,"ax",@progbits
> - .align 2
> + .p2align 2
> .globl _init
> .hidden _init
> .type _init, @function
> @@ -74,7 +74,7 @@
> #endif
>
> .section .fini,"ax",@progbits
> - .align 2
> + .p2align 2
> .globl _fini
> .hidden _fini
> .type _fini, @function
>
>
> I did try this out, and it largely seemed to work, although processes
> occasionally hung. Perhaps this was unrelated.
I was just looking at the necessary changes to switch m68k to 32-bit alignment
and I'm not sure we need to do anything about glibc. I am documenting my current
findings here [1].
What I have found out so far is that official ELF ABI documentation from AT&T
mandates a default alignment of four bytes and any SVR4-based distribution such
as Amiga Unix and NetBSD/ELF actually adheres to that. Why Linux uses a 2 bytes
alignment when the official ELF ABI documentation clearly says 4 bytes, remains
a mystery to me.
If we are willing to guess, I'd say it's because it is the norm in AmigaOS.
I'm not even sure whether we would have to change the target triplet since the
current implementation for Linux is actually violating the standard and any
application adhering to spec written for Linux ELF m68k would actually not work.
Anyway, looking at crti.s for other 32-bit architectures such as powerpc, I'm not
sure we actually need to do anything about glibc. I think just changing the
default value for BIGGEST_ALIGNMENT from 16 to 64 similar to NetBSD/ELF in GCC
should be enough, shouldn't it?
Adrian
> [1] https://wiki.debian.org/M68k/Alignment
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer
`. `' Physicist
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