alloc-variant-zeroed causing issues with LTO

@aeubanks

I believe this causing https://crbug.com/441524277. In summary, the rust calloc function _RNvCsfo6nMSlQo1l_7___rustc19___rust_alloc_zeroed definition does not have the alloc-family attribute, but user modules of it have the alloc-family attribute on the calloc declaration. however, if ThinLTO decides to import the function, we lose the alloc-family attribute and the verifier complains 'alloc-variant-zeroed' must name a function belonging to the same 'alloc-family'.

Originally posted by @aeubanks in #144086 (comment)

followup to #144086 (comment)

$ cat src/main.rs

mod foobar {
    use std::alloc::{GlobalAlloc, Layout};

    struct Allocator;

    unsafe impl GlobalAlloc for Allocator {
        unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
            panic!()
        }

        unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
            panic!()
        }

        unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
            panic!()
        }

        unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
            panic!()
        }
    }

    #[global_allocator]
    static GLOBAL: Allocator = Allocator;
}


fn main() {
    println!("Hello, world!");
}

$ RUSTFLAGS='--emit=llvm-ir' cargo build --release

no sign of the alloc-family attribute in the .ll file, which does contain definitions for the alloc functions

@rustbot

Assigning priority (discussion on Zulip).

@rustbot label -I-prioritize +P-high

any update on this? we have #144086 reverted in our ToT rustc build but that's not sustainable

Visited during compiler team triage meeting, we recommend considering a revert & re-apply of the injecting PR after this issue has been resolved.

Forwarding from Zulip: If no global_allocator is specified the function definitions are generated at:

rust/compiler/rustc_codegen_llvm/src/allocator.rs

Lines 18 to 63 in 32e3d9f

    
           pub(crate) unsafe fn codegen( 
        
               tcx: TyCtxt<'_>, 
        
               cx: SimpleCx<'_>, 
        
               module_name: &str, 
        
               kind: AllocatorKind, 
        
               alloc_error_handler_kind: AllocatorKind, 
        
           ) { 
        
               let usize = match tcx.sess.target.pointer_width { 
        
                   16 => cx.type_i16(), 
        
                   32 => cx.type_i32(), 
        
                   64 => cx.type_i64(), 
        
                   tws => bug!("Unsupported target word size for int: {}", tws), 
        
               }; 
        
               let i8 = cx.type_i8(); 
        
               let i8p = cx.type_ptr(); 
        
               if kind == AllocatorKind::Default { 
        
                   for method in ALLOCATOR_METHODS { 
        
                       let mut args = Vec::with_capacity(method.inputs.len()); 
        
                       for input in method.inputs.iter() { 
        
                           match input.ty { 
        
                               AllocatorTy::Layout => { 
        
                                   args.push(usize); // size 
        
                                   args.push(usize); // align 
        
                               } 
        
                               AllocatorTy::Ptr => args.push(i8p), 
        
                               AllocatorTy::Usize => args.push(usize), 
        
                               AllocatorTy::ResultPtr | AllocatorTy::Unit => panic!("invalid allocator arg"), 
        
                           } 
        
                       } 
        
                       let output = match method.output { 
        
                           AllocatorTy::ResultPtr => Some(i8p), 
        
                           AllocatorTy::Unit => None, 
        
                           AllocatorTy::Layout | AllocatorTy::Usize | AllocatorTy::Ptr => { 
        
                               panic!("invalid allocator output") 
        
                           } 
        
                       }; 
        
                       let from_name = mangle_internal_symbol(tcx, &global_fn_name(method.name)); 
        
                       let to_name = mangle_internal_symbol(tcx, &default_fn_name(method.name)); 
        
                       create_wrapper_function(tcx, &cx, &from_name, Some(&to_name), &args, output, false); 
        
                   } 
        
               }

If global_allocator is specified it happens in the macro expansion, which is this file I believe: https://github.com/rust-lang/rust/blob/master/compiler/rustc_builtin_macros/src/global_allocator.rs So I guess we need to expand

rust/compiler/rustc_builtin_macros/src/global_allocator.rs

Lines 103 to 105 in 32e3d9f

    
           fn attrs(&self) -> AttrVec { 
        
               thin_vec![self.cx.attr_word(sym::rustc_std_internal_symbol, self.span)] 
        
           }

to include the usual allocator attributes.

Alternatively we could also drop the verifier checks on the LLVM side -- they are not required for correctness. Though it sounds like this did highlight a legitimate problem in this case.

Unrolled build for #146766

@aeubanks

@aeubanks Could you please confirm whether #146766 does indeed fix the original issue you saw?

Rollup merge of #146766 - nikic:global-alloc-attr, r=nnethercote

Auto merge of #147030 - nikic:revert-alloc-zeroed, r=wesleywiser

Rollup merge of rust-lang#147150 - nikic:alloc-shim-attributes, r=bjorn3

Unrolled build for #147150

@aeubanks

#147030 was merged to beta to revert the injecting PR and #147150 was merged to master to fix the actual issue thus I believe this can be closed.

@aeubanks if you are still observing this issue on beta or nightly, please let us know so we can reopen. Thanks!

Rollup merge of #146766 - nikic:global-alloc-attr, r=nnethercote

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`alloc-variant-zeroed` causing issues with LTO #145995

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	pub(crate) unsafe fn codegen(
	tcx: TyCtxt<'_>,
	cx: SimpleCx<'_>,
	module_name: &str,
	kind: AllocatorKind,
	alloc_error_handler_kind: AllocatorKind,
	) {
	let usize = match tcx.sess.target.pointer_width {
	16 => cx.type_i16(),
	32 => cx.type_i32(),
	64 => cx.type_i64(),
	tws => bug!("Unsupported target word size for int: {}", tws),
	};
	let i8 = cx.type_i8();
	let i8p = cx.type_ptr();

	if kind == AllocatorKind::Default {
	for method in ALLOCATOR_METHODS {
	let mut args = Vec::with_capacity(method.inputs.len());
	for input in method.inputs.iter() {
	match input.ty {
	AllocatorTy::Layout => {
	args.push(usize); // size
	args.push(usize); // align
	}
	AllocatorTy::Ptr => args.push(i8p),
	AllocatorTy::Usize => args.push(usize),

	AllocatorTy::ResultPtr \| AllocatorTy::Unit => panic!("invalid allocator arg"),
	}
	}
	let output = match method.output {
	AllocatorTy::ResultPtr => Some(i8p),
	AllocatorTy::Unit => None,

	AllocatorTy::Layout \| AllocatorTy::Usize \| AllocatorTy::Ptr => {
	panic!("invalid allocator output")
	}
	};

	let from_name = mangle_internal_symbol(tcx, &global_fn_name(method.name));
	let to_name = mangle_internal_symbol(tcx, &default_fn_name(method.name));

	create_wrapper_function(tcx, &cx, &from_name, Some(&to_name), &args, output, false);
	}
	}

	fn attrs(&self) -> AttrVec {
	thin_vec![self.cx.attr_word(sym::rustc_std_internal_symbol, self.span)]
	}

alloc-variant-zeroed causing issues with LTO #145995

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aeubanks commented on Sep 3, 2025

apiraino commented on Sep 4, 2025

aeubanks commented on Sep 17, 2025

wesleywiser commented on Sep 18, 2025

nikic commented on Sep 18, 2025

10 remaining items

nikic commented on Sep 25, 2025

wesleywiser commented on Oct 9, 2025

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`alloc-variant-zeroed` causing issues with LTO #145995