Add initial support for m68k-unknown-linux-gnu

[glaubitz]

This adds initial support for m68k-unknown-linux-gnu to libc.

CC @ricky26 @jrtc27

[rust-highfive]

r? @JohnTitor

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[JohnTitor]

If it works fine on the platform, I could rubber-stamp this. Is the review from cc'd people complete?

[glaubitz]

I will have to fix the remaining issues first that @jrtc27 has mentioned. I'll ping you back once we're ready.

[glaubitz]

I will have to review all the constants again before we can consider this ready-for-merge.

[glaubitz]

@jrtc27 @JohnTitor I have updated the definitions now and they should now all be correct.

[glaubitz]

Could someone clear the S-waiting-on-author? Thanks!

[glaubitz]

@bors r?

[glaubitz]

r? @Amanieu

[Amanieu]

@bors r+

[bors]

📌 Commit 9fa467e has been approved by Amanieu

[glaubitz]

@jrtc27 Could you briefly comment on the max_align_t struct? I'm not sure I got it right:

#[allow(missing_debug_implementations)]
#[repr(align(2))]
pub struct max_align_t {
       priv_: [i8; 12]
}

@Amanieu I'm not sure whether the current max_align_t matches what the glibc does.

[Amanieu]

My recommendation would be to check against a m68k C toolchain:

#include <stddef.h>
int foo = sizeof(max_align_t);

Generate assembly code with -S and check the value of foo.

@bors r-

Let me know once you've checked the value.

[glaubitz]

@Amanieu Perfect, thank you! That's what I was looking for!

[glaubitz]

OK, it's 20 bytes:

#NO_APP
        .file   "max_align.c"
        .text
        .globl  foo
        .data
        .align  2
        .type   foo, @object
        .size   foo, 4
foo:
        .long   20
        .ident  "GCC: (Debian 11.2.0-14) 11.2.0"
        .section        .note.GNU-stack,"",@progbits

Not sure how that translates into the Rust struct.

Would that be:

#[allow(missing_debug_implementations)]
#[repr(align(2))]
pub struct max_align_t {
       priv_: [i8; 20]
}

?

[glaubitz]

@Amanieu I think it should be correct now. The overall size is 20 bytes which can be represented by [i8; 20].

[Amanieu]

@bors r+

[bors]

📌 Commit 7a027d3 has been approved by Amanieu

[bors]

⌛ Testing commit 7a027d3 with merge 6449ebc...

[bors]

☀️ Test successful - checks-actions, checks-cirrus-freebsd-11, checks-cirrus-freebsd-12, checks-cirrus-freebsd-13
Approved by: Amanieu
Pushing 6449ebc to master...