From 952da9c95080ea2a5ec8d129e88cda878996acb4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Aur=C3=A9lien=20Nicolas?= <info@nau.re>
Date: Thu, 12 Dec 2024 02:56:18 +0100
Subject: [PATCH] sync-platform: remove stack_top

---
 ceno_emul/src/platform.rs | 10 ++++------
 ceno_emul/src/vm_state.rs |  2 +-
 ceno_zkvm/src/e2e.rs      |  4 ++--
 3 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/ceno_emul/src/platform.rs b/ceno_emul/src/platform.rs
index 40bb09230..0f7c5112d 100644
--- a/ceno_emul/src/platform.rs
+++ b/ceno_emul/src/platform.rs
@@ -16,7 +16,6 @@ pub struct Platform {
     pub heap: Range<Addr>,
     pub public_io: Range<Addr>,
     pub hints: Range<Addr>,
-    pub stack_top: Addr, // TODO: remove.
     /// If true, ecall instructions are no-op instead of trap. Testing only.
     pub unsafe_ecall_nop: bool,
 }
@@ -29,7 +28,6 @@ pub const CENO_PLATFORM: Platform = Platform {
     heap: 0x8000_0000..0xFFFF_0000,
     public_io: 0x3000_1000..0x3000_2000,
     hints: 0x4000_0000..0x5000_0000,
-    stack_top: 0xC0000000,
     unsafe_ecall_nop: false,
 };
 
@@ -82,11 +80,11 @@ impl Platform {
     // Permissions.
 
     pub fn can_read(&self, addr: Addr) -> bool {
-        self.is_rom(addr) || self.is_ram(addr) || self.is_pub_io(addr) || self.is_hints(addr)
+        self.can_write(addr)
     }
 
     pub fn can_write(&self, addr: Addr) -> bool {
-        self.is_ram(addr)
+        self.is_ram(addr) || self.is_pub_io(addr) || self.is_hints(addr)
     }
 
     pub fn can_execute(&self, addr: Addr) -> bool {
@@ -131,8 +129,8 @@ mod tests {
         let p = CENO_PLATFORM;
         assert!(p.can_execute(p.pc_base()));
         // ROM and RAM do not overlap.
-        assert!(!p.is_rom(p.ram.start));
-        assert!(!p.is_rom(p.ram.end - WORD_SIZE as Addr));
+        assert!(!p.is_rom(p.heap.start));
+        assert!(!p.is_rom(p.heap.end - WORD_SIZE as Addr));
         assert!(!p.is_ram(p.rom.start));
         assert!(!p.is_ram(p.rom.end - WORD_SIZE as Addr));
         // Registers do not overlap with ROM or RAM.
diff --git a/ceno_emul/src/vm_state.rs b/ceno_emul/src/vm_state.rs
index e071cb000..3ad4cdec2 100644
--- a/ceno_emul/src/vm_state.rs
+++ b/ceno_emul/src/vm_state.rs
@@ -123,7 +123,7 @@ impl EmuContext for VMState {
             tracing::warn!("ecall ignored: syscall_id={}", function);
             self.store_register(DecodedInstruction::RD_NULL as RegIdx, 0)?;
             // Example ecall effect - any writable address will do.
-            let addr = (self.platform.stack_top - WORD_SIZE as u32).into();
+            let addr = (self.platform.stack.end - WORD_SIZE as u32).into();
             self.store_memory(addr, self.peek_memory(addr))?;
             self.set_pc(ByteAddr(self.pc) + PC_STEP_SIZE);
             Ok(true)
diff --git a/ceno_zkvm/src/e2e.rs b/ceno_zkvm/src/e2e.rs
index 32ca4c2c8..3c2d0c690 100644
--- a/ceno_zkvm/src/e2e.rs
+++ b/ceno_zkvm/src/e2e.rs
@@ -177,7 +177,7 @@ pub fn setup_platform(
         Preset::Ceno => CENO_PLATFORM,
         Preset::Sp1 => Platform {
             // The stack section is not mentioned in ELF headers, so we repeat the constant STACK_TOP here.
-            stack_top: 0x0020_0400,
+            stack: 0x0020_0400..0x0020_0400,
             ram: 0x0010_0000..0xFFFF_0000,
             unsafe_ecall_nop: true,
             ..CENO_PLATFORM
@@ -185,7 +185,7 @@ pub fn setup_platform(
     };
 
     let prog_data = program.image.keys().copied().collect::<HashSet<Addr>>();
-    let stack = preset.stack_top - stack_size..preset.stack_top;
+    let stack = preset.stack.end - stack_size..preset.stack.end;
     let heap = {
         // Detect heap as starting after program data.
         let heap_start = program.image.keys().max().unwrap() + WORD_SIZE as u32;