#![no_builtins] attribute isn't honored

[kellda]

#![no_std]
#![no_builtins]

#[no_mangle]
#[inline(never)]
pub unsafe fn set_bytes_bytes(mut s: *mut u8, c: u8, n: usize) {
    let end = s.add(n);
    while s < end {
        *s = c;
        s = s.add(1);
    }
}

Even with the #![no_builtins] attribute, the above loop is replaced by a call to memset. This is problematic when compiling compiler_builtins, because memset end up recursively calling itself.

000003bc <set_bytes_bytes.constprop.0>:
     3bc:       9c 21 ff f8     l.addi r1,r1,-8
     3c0:       18 a0 00 08     l.movhi r5,0x8
     3c4:       18 80 00 00     l.movhi r4,0x0
     3c8:       d4 01 80 00     l.sw 0(r1),r16
     3cc:       d4 01 48 04     l.sw 4(r1),r9
     3d0:       04 00 00 02     l.jal 3d8 <set_bytes_bytes.constprop.0+0x1c>
     3d4:       1a 00 00 00     l.movhi r16,0x0
     3d8:       aa 10 52 08     l.ori r16,r16,0x5208
     3dc:       e2 10 48 00     l.add r16,r16,r9
     3e0:       04 00 0c 4a     l.jal 3508 <memset>
     3e4:       84 70 00 0c     l.lwz r3,12(r16)
     3e8:       85 21 00 04     l.lwz r9,4(r1)
     3ec:       86 01 00 00     l.lwz r16,0(r1)
     3f0:       44 00 48 00     l.jr r9
     3f4:       9c 21 00 08     l.addi r1,r1,8

[antoyo]

I guess this would be a matter of adding the flag -fno-builtin.

Assuming this doesn't break something else.

[Anon258]

@kellda What is the tool you have used here to inspect the asm? Is it cargo-asm?

[kellda]

No, it was plain old objdump -d or objdump -S

[Anon258]

I would like to work on this issue to learn more about the Rust compiler process. However I am not that well acquainted with rust compiler process. I have just read through the basic rust dev guide, can I still work on this issue?

[antoyo]

Yes, I assigned this issue to you.