allow dynamic configuration of the heap memory (#287)

This PR changes the implementation of the emulated EVM heap memory:
Instead of linking in a C implementation the code is emitted directly
into the contract module. Which allows making it configurable via a
compiler parameter (a follow up PR to this).

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/llvm-context/src/polkavm/context/function/runtime/entry.rs

@@ -31,6 +31,21 @@ impl Entry {
             context.xlen_type().get_undef(),
         );
 
+        context.set_global(
+            crate::polkavm::GLOBAL_HEAP_SIZE,
+            context.xlen_type(),
+            AddressSpace::Stack,
+            context.xlen_type().const_zero(),
+        );
+
+        let heap_memory_type = context.byte_type().array_type(context.heap_size);
+        context.set_global(
+            crate::polkavm::GLOBAL_HEAP_MEMORY,
+            heap_memory_type,
+            AddressSpace::Stack,
+            heap_memory_type.const_zero(),
+        );
+
         let address_type = context.integer_type(revive_common::BIT_LENGTH_ETH_ADDRESS);
         context.set_global(
             crate::polkavm::GLOBAL_ADDRESS_SPILL_BUFFER,

crates/llvm-context/src/polkavm/context/function/runtime/mod.rs

@@ -5,6 +5,7 @@ pub mod deploy_code;
 pub mod entry;
 pub mod revive;
 pub mod runtime_code;
+pub mod sbrk;
 
 /// The main entry function name.
 pub const FUNCTION_ENTRY: &str = "__entry";

crates/llvm-context/src/polkavm/context/function/runtime/sbrk.rs

@@ -0,0 +1,144 @@
+//! Emulates the linear EVM heap memory via a simulated `sbrk` system call.
+
+use inkwell::values::BasicValue;
+
+use crate::polkavm::context::attribute::Attribute;
+use crate::polkavm::context::runtime::RuntimeFunction;
+use crate::polkavm::context::Context;
+use crate::polkavm::Dependency;
+use crate::polkavm::WriteLLVM;
+
+/// Simulates the `sbrk` system call, reproducing the semantics of the EVM heap memory.
+///
+/// Parameters:
+/// - The `offset` into the emulated EVM heap memory.
+/// - The `size` of the allocation emulated EVM heap memory.
+///
+/// Returns:
+/// - A pointer to the EVM heap memory at given `offset`.
+///
+/// Semantics:
+/// - Traps if the offset is out of bounds.
+/// - Aligns the total heap memory size to the EVM word size.
+/// - Traps if the memory size would be greater than the configured EVM heap memory size.
+/// - Maintains the total memory size (`msize`) in global heap size value.
+pub struct Sbrk;
+
+impl<D> RuntimeFunction<D> for Sbrk
+where
+    D: Dependency + Clone,
+{
+    const NAME: &'static str = "__sbrk_internal";
+
+    const ATTRIBUTES: &'static [Attribute] = &[
+        Attribute::NoFree,
+        Attribute::NoRecurse,
+        Attribute::WillReturn,
+    ];
+
+    fn r#type<'ctx>(context: &Context<'ctx, D>) -> inkwell::types::FunctionType<'ctx> {
+        context.llvm().ptr_type(Default::default()).fn_type(
+            &[context.xlen_type().into(), context.xlen_type().into()],
+            false,
+        )
+    }
+
+    fn emit_body<'ctx>(
+        &self,
+        context: &mut Context<'ctx, D>,
+    ) -> anyhow::Result<Option<inkwell::values::BasicValueEnum<'ctx>>> {
+        let offset = Self::paramater(context, 0).into_int_value();
+        let size = Self::paramater(context, 1).into_int_value();
+
+        let trap_block = context.append_basic_block("trap");
+        let offset_in_bounds_block = context.append_basic_block("offset_in_bounds");
+        let is_offset_out_of_bounds = context.builder().build_int_compare(
+            inkwell::IntPredicate::UGE,
+            offset,
+            context.heap_size(),
+            "offset_out_of_bounds",
+        )?;
+        context.build_conditional_branch(
+            is_offset_out_of_bounds,
+            trap_block,
+            offset_in_bounds_block,
+        )?;
+
+        context.set_basic_block(trap_block);
+        context.build_call(context.intrinsics().trap, &[], "invalid_trap");
+        context.build_unreachable();
+
+        context.set_basic_block(offset_in_bounds_block);
+        let mask = context
+            .xlen_type()
+            .const_int(revive_common::BYTE_LENGTH_WORD as u64 - 1, false);
+        let total_size = context
+            .builder()
+            .build_int_add(offset, size, "total_size")?;
+        let memory_size = context.builder().build_and(
+            context.builder().build_int_add(total_size, mask, "mask")?,
+            context.builder().build_not(mask, "mask_not")?,
+            "memory_size",
+        )?;
+        let size_in_bounds_block = context.append_basic_block("size_in_bounds");
+        let is_size_out_of_bounds = context.builder().build_int_compare(
+            inkwell::IntPredicate::UGT,
+            memory_size,
+            context.heap_size(),
+            "size_out_of_bounds",
+        )?;
+        context.build_conditional_branch(
+            is_size_out_of_bounds,
+            trap_block,
+            size_in_bounds_block,
+        )?;
+
+        context.set_basic_block(size_in_bounds_block);
+        let return_block = context.append_basic_block("return_pointer");
+        let new_size_block = context.append_basic_block("new_size");
+        let is_new_size = context.builder().build_int_compare(
+            inkwell::IntPredicate::UGT,
+            memory_size,
+            context
+                .get_global_value(crate::polkavm::GLOBAL_HEAP_SIZE)?
+                .into_int_value(),
+            "is_new_size",
+        )?;
+        context.build_conditional_branch(is_new_size, new_size_block, return_block)?;
+
+        context.set_basic_block(new_size_block);
+        context.build_store(
+            context.get_global(crate::polkavm::GLOBAL_HEAP_SIZE)?.into(),
+            memory_size,
+        )?;
+        context.build_unconditional_branch(return_block);
+
+        context.set_basic_block(return_block);
+        Ok(Some(
+            context
+                .build_gep(
+                    context
+                        .get_global(crate::polkavm::GLOBAL_HEAP_MEMORY)?
+                        .into(),
+                    &[context.xlen_type().const_zero(), offset],
+                    context.byte_type(),
+                    "allocation_start_pointer",
+                )
+                .value
+                .as_basic_value_enum(),
+        ))
+    }
+}
+
+impl<D> WriteLLVM<D> for Sbrk
+where
+    D: Dependency + Clone,
+{
+    fn declare(&mut self, context: &mut Context<D>) -> anyhow::Result<()> {
+        <Self as RuntimeFunction<_>>::declare(self, context)
+    }
+
+    fn into_llvm(self, context: &mut Context<D>) -> anyhow::Result<()> {
+        <Self as RuntimeFunction<_>>::emit(&self, context)
+    }
+}