diff --git a/.envrc b/.envrc
new file mode 100644
index 0000000..1d953f4
--- /dev/null
+++ b/.envrc
@@ -0,0 +1 @@
+use nix
diff --git a/analysis/src/ir.rs b/analysis/src/ir.rs
index 164a449..8a5d80c 100644
--- a/analysis/src/ir.rs
+++ b/analysis/src/ir.rs
@@ -131,8 +131,8 @@ pub struct Statement {
 pub enum StatementKind {
     Alloca {
         result: Register,
-        size: Operand,
-        align: Operand,
+        size: u64,
+        align: u64,
     },
     Store {
         ptr: Operand,
@@ -234,6 +234,8 @@ impl Func<'_> {
 }
 
 impl BbIdx {
+    pub const ZERO: Self = Self(0);
+
     pub fn from_usize(n: usize) -> Self {
         Self(n.try_into().unwrap())
     }
diff --git a/analysis/src/ir/info.rs b/analysis/src/ir/info.rs
index 61cabf2..66d3f6e 100644
--- a/analysis/src/ir/info.rs
+++ b/analysis/src/ir/info.rs
@@ -4,7 +4,7 @@ use super::{BbIdx, Branch, Func, Location, Operand};
 use crate::ir::visit::Visitor;
 
 pub fn traverse_postorder(func: &Func<'_>) -> Vec<BbIdx> {
-    // the final traversial, backwards.
+    // the final traversal, backwards.
     // the starting bb has to be visited last.
     let mut traversal = vec![BbIdx(0)];
     let mut i = 0;
diff --git a/analysis/src/ir/pretty.rs b/analysis/src/ir/pretty.rs
index 1ea52c8..b294f71 100644
--- a/analysis/src/ir/pretty.rs
+++ b/analysis/src/ir/pretty.rs
@@ -33,7 +33,7 @@ impl<'a> Customizer<'a> for DefaultCustomizer<'a> {
         self.0.set(Some(func));
     }
 
-    fn fmt_reg(&self, reg: Register, f: &mut fmt::Formatter<'_>, loc: Location) -> fmt::Result {
+    fn fmt_reg(&self, reg: Register, f: &mut fmt::Formatter<'_>, _loc: Location) -> fmt::Result {
         match self.0.get().unwrap().regs[reg.0 as usize].name {
             None => write!(f, "%{}", reg.0),
             Some(name) => write!(f, "%{name}"),
@@ -101,10 +101,8 @@ impl<W: Write> PrettyPrinter<W> {
                     } => {
                         writeln!(
                             self.out,
-                            "    {} = alloca, size={}, align={}",
+                            "    {} = alloca, size={size}, align={align}",
                             print_reg(reg),
-                            print_op(size),
-                            print_op(align)
                         )
                     }
                     StatementKind::Store {
diff --git a/analysis/src/ir/validate.rs b/analysis/src/ir/validate.rs
index abb1aff..a28798a 100644
--- a/analysis/src/ir/validate.rs
+++ b/analysis/src/ir/validate.rs
@@ -1,6 +1,6 @@
 use rustc_hash::FxHashSet;
 
-use super::{visit::Visitor, Branch, Func, Register};
+use super::{visit::Visitor, Branch, Func, Register, StatementKind};
 use crate::ir::BbIdx;
 
 pub fn validate(func: &Func<'_>) {
@@ -14,6 +14,16 @@ pub fn validate(func: &Func<'_>) {
         }
     }
 
+    for (i, bb) in func.bbs.iter().enumerate().skip(1) {
+        if bb
+            .statements
+            .iter()
+            .any(|stmt| matches!(stmt.kind, StatementKind::Alloca { .. }))
+        {
+            panic!("alloca is only allowed in first block, found in block {i}")
+        }
+    }
+
     let mut reg_names = FxHashSet::default();
     for reg in &func.regs {
         if let Some(name) = reg.name {
diff --git a/analysis/src/ir/visit.rs b/analysis/src/ir/visit.rs
index 882dfd5..4c8cce3 100644
--- a/analysis/src/ir/visit.rs
+++ b/analysis/src/ir/visit.rs
@@ -32,12 +32,10 @@ pub trait Visitor {
         match stmt.kind {
             StatementKind::Alloca {
                 result,
-                size,
-                align,
+                size: _,
+                align: _,
             } => {
                 self.visit_reg(result);
-                self.visit_operand(size);
-                self.visit_operand(align);
             }
             StatementKind::Store {
                 ptr,
diff --git a/analysis/src/lower.rs b/analysis/src/lower.rs
index faaf4a7..ee73ef2 100644
--- a/analysis/src/lower.rs
+++ b/analysis/src/lower.rs
@@ -116,7 +116,7 @@ impl<'a, 'cx> FnLoweringCtxt<'a, 'cx> {
         for (var, def_span) in &decl.init_declarators {
             let tyl = self.lcx.layout_of(ty);
             let (name, name_span) = var.declarator.decl.name();
-            let ptr_to = self.build.alloca(tyl.layout, Some(name), span);
+            let ptr_to = self.build.reserve_local(tyl.layout, name, span);
 
             let variable_info = VariableInfo {
                 def_span: *def_span,
@@ -478,7 +478,7 @@ fn lower_func<'cx>(
         let span = param.declarator.1;
 
         let alloca_name = Symbol::intern(&format!("{}.local", name));
-        let ptr_to = cx.build.alloca(tyl.layout, Some(alloca_name), span);
+        let ptr_to = cx.build.reserve_local(tyl.layout, alloca_name, span);
 
         let variable_info = VariableInfo {
             def_span: span,
diff --git a/analysis/src/lower/builder.rs b/analysis/src/lower/builder.rs
index b5f8ae4..fa2dd3b 100644
--- a/analysis/src/lower/builder.rs
+++ b/analysis/src/lower/builder.rs
@@ -3,8 +3,8 @@ use parser::{Span, Symbol};
 use super::LoweringCx;
 use crate::{
     ir::{
-        self, BasicBlock, BbIdx, BinKind, Branch, ConstValue, Func, Layout, Operand, Register,
-        RegisterData, Statement, StatementKind, TyLayout, UnaryKind,
+        self, BasicBlock, BbIdx, BinKind, Branch, Func, Layout, Operand, Register, RegisterData,
+        Statement, StatementKind, TyLayout, UnaryKind,
     },
     ty::{Ty, TyKind},
 };
@@ -47,6 +47,15 @@ impl<'a, 'cx> FuncBuilder<'a, 'cx> {
         reg
     }
 
+    pub fn reserve_local(&mut self, layout: &Layout, name: Symbol, span: Span) -> Register {
+        // Every local is a singleton.
+        let prev = self.current_bb;
+        self.current_bb = BbIdx(0);
+        let reg = self.alloca(layout, Some(name), span);
+        self.current_bb = prev;
+        reg
+    }
+
     pub fn alloca(&mut self, layout: &Layout, name: Option<Symbol>, span: Span) -> Register {
         let void_ptr = self
             .lcx
@@ -56,8 +65,8 @@ impl<'a, 'cx> FuncBuilder<'a, 'cx> {
             span,
             kind: StatementKind::Alloca {
                 result: reg,
-                size: Operand::Const(ConstValue::u64(layout.size)),
-                align: Operand::Const(ConstValue::u64(layout.align)),
+                size: layout.size,
+                align: layout.align,
             },
         };
         self.cur_bb_mut().statements.push(stmt);
diff --git a/codegen/src/lib.rs b/codegen/src/lib.rs
index d92d668..a82d069 100644
--- a/codegen/src/lib.rs
+++ b/codegen/src/lib.rs
@@ -1,4 +1,5 @@
 mod registers;
+mod stack;
 mod x86_64;
 
 use std::process::Stdio;
diff --git a/codegen/src/registers.rs b/codegen/src/registers.rs
index dc2d6c4..e57604a 100644
--- a/codegen/src/registers.rs
+++ b/codegen/src/registers.rs
@@ -53,7 +53,7 @@ pub struct MachineReg(pub usize);
 pub enum RegValue {
     /// The SSA register contains an address on the stack.
     /// The offset is the offset from the start of the function.
-    StackRelative { offset: u64 },
+    StackRelativePtr { offset: u64 },
     /// The SSA register resides on the stack as it has been spilled.
     /// This should be rather rare in practice.
     Spilled { offset: u64 },
@@ -65,15 +65,13 @@ pub enum RegValue {
 pub struct FunctionLayout {
     /// Where a register comes from at a particular usage of a register.
     register_uses: FxHashMap<(Location, Register), RegValue>,
-    total_stack_space: u64,
 }
 
-pub fn compute_layout(f: &Func) -> FunctionLayout {
+pub fn compute_layout(_f: &Func) -> FunctionLayout {
     let register_uses = FxHashMap::default();
 
     FunctionLayout {
         register_uses,
-        total_stack_space: 0,
     }
 }
 
@@ -102,7 +100,7 @@ impl<'a> ir::pretty::Customizer<'a> for LayoutPrinter<'a> {
         match layout {
             Some(RegValue::MachineReg(mach)) => write!(f, "reg-{}", mach.0)?,
             Some(RegValue::Spilled { offset }) => write!(f, "spill-{offset}")?,
-            Some(RegValue::StackRelative { offset }) => {
+            Some(RegValue::StackRelativePtr { offset }) => {
                 write!(f, "i-forgot-what-this-meant-{offset}")?
             }
             None => write!(f, "<unknown>")?,
diff --git a/codegen/src/stack.rs b/codegen/src/stack.rs
new file mode 100644
index 0000000..16da9b2
--- /dev/null
+++ b/codegen/src/stack.rs
@@ -0,0 +1,43 @@
+use std::collections::HashMap;
+
+use analysis::ir::{BbIdx, Func, Register, StatementKind};
+
+#[derive(Debug)]
+pub struct StackLayout {
+    pub allocas: HashMap<Register, u64>,
+    pub total_size: u64,
+}
+
+/// Based on the alloca's in the initial block, this calculcates stack pointer offsets for every allocation.
+pub fn allocate_stack_space<'cx>(start_align: u64, func: &Func<'cx>) -> StackLayout {
+    assert_eq!(start_align, 8);
+    // REMEMBER: The stack grows down (on x86-64).
+
+    let mut temp_layout = HashMap::new();
+    let mut offset_backwards = 0;
+
+    for stmt in &func.bb(BbIdx::ZERO).statements {
+        if let StatementKind::Alloca {
+            result,
+            size,
+            align,
+        } = stmt.kind
+        {
+            if size != 8 || align != 8 {
+                todo!("non 8 integer {size} {align}")
+            }
+            offset_backwards += 8;
+            temp_layout.insert(result, offset_backwards);
+        }
+    }
+
+    let total_size = offset_backwards;
+
+    StackLayout {
+        allocas: temp_layout
+            .into_iter()
+            .map(|(reg, offset_back)| (reg, total_size - offset_back))
+            .collect(),
+        total_size,
+    }
+}
diff --git a/codegen/src/x86_64.rs b/codegen/src/x86_64.rs
index 6899be9..1d48ab4 100644
--- a/codegen/src/x86_64.rs
+++ b/codegen/src/x86_64.rs
@@ -40,7 +40,7 @@ use rustc_hash::FxHashMap;
 
 use crate::{
     registers::{MachineReg, RegValue},
-    Result,
+    stack, Result,
 };
 
 trait IcedErrExt {
@@ -61,9 +61,10 @@ struct AsmCtxt<'cx> {
     a: CodeAssembler,
     reg_map: FxHashMap<Register, RegValue>,
     reg_occupancy: Vec<Option<Register>>,
-    current_stack_offset: u64,
     bb_idx: BbIdx,
 
+    stack_layout: stack::StackLayout,
+
     // caches
     last_register_uses: Vec<Option<Location>>,
 }
@@ -98,6 +99,9 @@ impl<'cx> AsmCtxt<'cx> {
         // Prologue: Save rbp and save rsp in rbp.
         self.a.push(x::rbp).sp(func.def_span)?;
         self.a.mov(x::rbp, x::rsp).sp(func.def_span)?;
+        self.a
+            .sub(x::rsp, self.stack_layout.total_size as i32)
+            .sp(func.def_span)?;
 
         loop {
             let bb = &func.bbs[self.bb_idx.as_usize()];
@@ -108,27 +112,15 @@ impl<'cx> AsmCtxt<'cx> {
                 } = *stmt;
 
                 match *kind {
-                    StatementKind::Alloca {
-                        result: reg,
-                        size,
-                        align: _,
-                    } => {
-                        // For alloca, we allocate some space on the stack by subtracting from RSP.
-                        // TODO: Align
-                        match size {
-                            Operand::Const(c) => {
-                                let offset = c.as_i32();
-                                self.a.sub(x::rsp, offset).sp(st_sp)?;
-                                self.current_stack_offset += offset as u64;
-                            }
-                            Operand::Reg(_) => {
-                                todo!("dynamic alloca is not supported. get a better computer")
-                            }
-                        };
+                    StatementKind::Alloca { result, .. } => {
                         self.reg_map.insert(
-                            reg,
-                            RegValue::StackRelative {
-                                offset: self.current_stack_offset,
+                            result,
+                            RegValue::StackRelativePtr {
+                                offset: *self
+                                    .stack_layout
+                                    .allocas
+                                    .get(&result)
+                                    .expect("no stack layout slot present for alloc register"),
                             },
                         );
                     }
@@ -149,14 +141,15 @@ impl<'cx> AsmCtxt<'cx> {
                             Operand::Reg(reg) => {
                                 let ptr_value = self.reg_map[&reg];
                                 match (ptr_value, value) {
-                                    (RegValue::StackRelative { offset }, Operand::Const(c)) => {
-                                        let offset_from_cur = self.current_stack_offset - offset;
-
+                                    (RegValue::StackRelativePtr { offset }, Operand::Const(c)) => {
                                         self.a
-                                            .mov(x::qword_ptr(x::rsp + offset_from_cur), c.as_i32())
+                                            .mov(x::qword_ptr(x::rsp + offset), c.as_i32())
                                             .sp(st_sp)?;
                                     }
-                                    (RegValue::StackRelative { offset }, Operand::Reg(value)) => {
+                                    (
+                                        RegValue::StackRelativePtr { offset },
+                                        Operand::Reg(value),
+                                    ) => {
                                         todo!("stack relative ptr + reg value")
                                     }
                                     (RegValue::Spilled { .. }, _) => todo!("spilled"),
@@ -229,13 +222,16 @@ pub fn generate_func<'cx>(lcx: &'cx LoweringCx<'cx>, func: &Func<'cx>) -> Result
     let fn_sp = func.def_span;
     let a = CodeAssembler::new(64).sp(fn_sp)?;
 
+    let stack_layout = stack::allocate_stack_space(8, func);
+    dbg!(&stack_layout);
+
     let mut cx = AsmCtxt {
         lcx,
         a,
         reg_map: FxHashMap::default(),
         reg_occupancy: vec![None; 8],
-        current_stack_offset: 0,
         bb_idx: BbIdx(0),
+        stack_layout,
         last_register_uses: ir::info::last_register_uses(func),
     };
 
diff --git a/flake.lock b/flake.lock
deleted file mode 100644
index f121b62..0000000
--- a/flake.lock
+++ /dev/null
@@ -1,26 +0,0 @@
-{
-  "nodes": {
-    "nixpkgs": {
-      "locked": {
-        "lastModified": 1685199731,
-        "narHash": "sha256-t8I2oEFetISWpY4NUydCNcDJLSBGGyMCeozzVborlZA=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "3580ac6c65ec97ebccb02c166af8d19045d4d291",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
-    "root": {
-      "inputs": {
-        "nixpkgs": "nixpkgs"
-      }
-    }
-  },
-  "root": "root",
-  "version": 7
-}
diff --git a/flake.nix b/flake.nix
deleted file mode 100644
index b4c7407..0000000
--- a/flake.nix
+++ /dev/null
@@ -1,40 +0,0 @@
-{
-  description = "the uwucc c compiler";
-
-  inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs"; # also valid: "nixpkgs"
-  };
-
-  outputs = { self, nixpkgs }:
-    let
-      allSystems = [
-        "x86_64-linux" # 64-bit Intel/AMD Linux
-        "aarch64-linux" # 64-bit ARM Linux
-        "x86_64-darwin" # 64-bit Intel macOS
-        "aarch64-darwin" # 64-bit ARM macOS
-      ];
-
-      # Helper to provide system-specific attributes
-      forAllSystems = f: nixpkgs.lib.genAttrs allSystems (system: f {
-        pkgs = import nixpkgs { inherit system; };
-      });
-    in
-    {
-      devShells = forAllSystems ({ pkgs }: {
-        default = pkgs.mkShell {
-          buildInputs = with pkgs; [
-            clang
-            llvmPackages_16.bintools
-            rustup
-            cargo-insta
-            gdb
-          ];
-
-          shellHook = ''
-            export PATH=$PATH:''${CARGO_HOME:-~/.cargo}/bin
-            export PATH=$PATH:''${RUSTUP_HOME:-~/.rustup}/toolchains/$RUSTC_VERSION-x86_64-unknown-linux-gnu/bin/
-          '';
-        };
-      });
-    };
-}
diff --git a/shell.nix b/shell.nix
new file mode 100644
index 0000000..583e343
--- /dev/null
+++ b/shell.nix
@@ -0,0 +1,15 @@
+{ pkgs ? import <nixpkgs> { } }: pkgs.mkShell
+{
+  buildInputs = with pkgs; [
+    clang
+    llvmPackages_16.bintools
+    rustup
+    cargo-insta
+    gdb
+  ];
+
+  shellHook = ''
+    export PATH=$PATH:''${CARGO_HOME:-~/.cargo}/bin
+    export PATH=$PATH:''${RUSTUP_HOME:-~/.rustup}/toolchains/$RUSTC_VERSION-x86_64-unknown-linux-gnu/bin/
+  '';
+}