fix: Over-align public constants in moduli_init (#2150)

The `two_modular_limbs_list` constant declared by `moduli_init!` and
used later in the complex setup macro was not guaranteed to be aligned
to a large enough alignment. This caused an issue in some use-case.

This change aligns the public constant `two_modular_limbs_list` to the
max block size of a modulus among all moduli declared to ensure no
memory alignment issues arise.

Fixes INT-5135

---------

Co-authored-by: Jonathan Wang <[email protected]>

Author: Avaneesh-axiom

extensions/algebra/complex-macros/src/lib.rs

@@ -649,7 +649,7 @@ pub fn complex_init(input: TokenStream) -> TokenStream {
                 #[cfg(target_os = "zkvm")]
                 {
                     use super::openvm_intrinsics_meta_do_not_type_this_by_yourself::{two_modular_limbs_list, limb_list_borders};
-                    let two_modulus_bytes = &two_modular_limbs_list[limb_list_borders[#mod_idx]..limb_list_borders[#mod_idx + 1]];
+                    let two_modulus_bytes = &two_modular_limbs_list.0[limb_list_borders[#mod_idx]..limb_list_borders[#mod_idx + 1]];
 
                     // We are going to use the numeric representation of the `rs2` register to distinguish the chip to setup.
                     // The transpiler will transform this instruction, based on whether `rs2` is `x0` or `x1`, into a `SETUP_ADDSUB` or `SETUP_MULDIV` instruction.

extensions/algebra/moduli-macros/src/lib.rs

@@ -973,6 +973,8 @@ pub fn moduli_init(input: TokenStream) -> TokenStream {
 
     let span = proc_macro::Span::call_site();
 
+    let mut max_block_size = 4;
+
     for (mod_idx, item) in items.into_iter().enumerate() {
         let modulus = item.value();
         let modulus_bytes = string_to_bytes(&modulus);
@@ -988,6 +990,8 @@ pub fn moduli_init(input: TokenStream) -> TokenStream {
             panic!("limbs must be at most 48");
         }
 
+        max_block_size = max_block_size.max(block_size);
+
         let block_size = proc_macro::Literal::usize_unsuffixed(block_size);
         let block_size = syn::Lit::new(block_size.to_string().parse::<_>().unwrap());
 
@@ -1152,6 +1156,9 @@ pub fn moduli_init(input: TokenStream) -> TokenStream {
         });
     }
 
+    let max_block_size = proc_macro::Literal::usize_unsuffixed(max_block_size);
+    let max_block_size = syn::Lit::new(max_block_size.to_string().parse::<_>().unwrap());
+
     let total_limbs_cnt = two_modular_limbs_flattened_list.len();
     let cnt_limbs_list_len = limb_list_borders.len();
     TokenStream::from(quote::quote_spanned! { span.into() =>
@@ -1162,7 +1169,10 @@ pub fn moduli_init(input: TokenStream) -> TokenStream {
         }
         #[allow(non_snake_case, non_upper_case_globals)]
         pub mod openvm_intrinsics_meta_do_not_type_this_by_yourself {
-            pub const two_modular_limbs_list: [u8; #total_limbs_cnt] = [#(#two_modular_limbs_flattened_list),*];
+            #[repr(C, align(#max_block_size))]
+            pub struct Aligned<T>(pub T);
+
+            pub const two_modular_limbs_list: Aligned<[u8; #total_limbs_cnt]> = Aligned([#(#two_modular_limbs_flattened_list),*]);
             pub const limb_list_borders: [usize; #cnt_limbs_list_len] = [#(#limb_list_borders),*];
         }
     })