fix(mm): fix brk syscall to properly map heap pages (#92)

* fix(mm): fix brk syscall to properly map heap pages

The original brk implementation had several issues:
1. Never actually mapped pages - only updated the heap_top pointer
2. Limit was USER_HEAP_SIZE (64KB), too small for real programs
3. Did not track initial heap region, causing double-mapping errors

Changes:
- Actually call aspace.map() to map new heap pages on expansion
- Increase limit to USER_HEAP_SIZE_MAX (512MB)
- Track initial_heap_end to avoid re-mapping already mapped pages
- Add USER_HEAP_SIZE_MAX config for all architectures

* modify files matching rustmft expects

* Change signal trampoline address

* adjust signal trampoline address

* modify brk as comments

* fix clippy

---------

Co-authored-by: sunhaosheng <sunhaosheng@kylinos.cn>

Author: sunhaosheng

api/src/syscall/mm/brk.rs

@@ -1,16 +1,55 @@
 use axerrno::AxResult;
+use axhal::paging::{MappingFlags, PageSize};
+use axmm::backend::Backend;
 use axtask::current;
-use starry_core::task::AsThread;
+use memory_addr::{VirtAddr, align_up_4k};
+use starry_core::{
+    config::{USER_HEAP_BASE, USER_HEAP_SIZE, USER_HEAP_SIZE_MAX},
+    task::AsThread,
+};
 
 pub fn sys_brk(addr: usize) -> AxResult<isize> {
     let curr = current();
     let proc_data = &curr.as_thread().proc_data;
-    let mut return_val: isize = proc_data.get_heap_top() as isize;
-    let heap_bottom = proc_data.get_heap_bottom() as usize;
-    if addr != 0 && addr >= heap_bottom && addr <= heap_bottom + starry_core::config::USER_HEAP_SIZE
-    {
-        proc_data.set_heap_top(addr);
-        return_val = addr as isize;
+    let current_top = proc_data.get_heap_top() as usize;
+    let heap_limit = USER_HEAP_BASE + USER_HEAP_SIZE_MAX;
+
+    if addr == 0 {
+        return Ok(current_top as isize);
+    }
+
+    if addr < USER_HEAP_BASE || addr > heap_limit {
+        return Ok(current_top as isize);
+    }
+
+    let new_top_aligned = align_up_4k(addr);
+    let current_top_aligned = align_up_4k(current_top);
+    // Initial heap region end address (already mapped during ELF loading)
+    let initial_heap_end = USER_HEAP_BASE + USER_HEAP_SIZE;
+
+    // Only map new pages when expanding beyond already mapped region
+    // Expansion start should be the greater of initial_heap_end and current_top_aligned
+    if new_top_aligned > current_top_aligned {
+        let expand_start = VirtAddr::from(initial_heap_end.max(current_top_aligned));
+        let expand_size = new_top_aligned.saturating_sub(expand_start.as_usize());
+
+        if expand_size > 0
+            && proc_data
+                .aspace
+                .lock()
+                .map(
+                    expand_start,
+                    expand_size,
+                    MappingFlags::READ | MappingFlags::WRITE | MappingFlags::USER,
+                    false,
+                    Backend::new_alloc(expand_start, PageSize::Size4K),
+                )
+                .is_err()
+        {
+            return Ok(current_top as isize);
+        }
     }
-    Ok(return_val)
+
+    proc_data.set_heap_top(addr);
+    Ok(addr as isize)
 }

core/src/config/aarch64.rs

@@ -15,9 +15,11 @@ pub const USER_STACK_SIZE: usize = 0x8_0000;
 pub const USER_HEAP_BASE: usize = 0x4000_0000;
 /// The size of the user heap.
 pub const USER_HEAP_SIZE: usize = 0x1_0000;
+/// The maximum size of the user heap (for brk expansion).
+pub const USER_HEAP_SIZE_MAX: usize = 0x2000_0000;
 
 /// The base address for user interpreter.
 pub const USER_INTERP_BASE: usize = 0x400_0000;
 
-/// The address of signal trampoline.
-pub const SIGNAL_TRAMPOLINE: usize = 0x4001_0000;
+/// The address of signal trampoline (placed at top of user heap).
+pub const SIGNAL_TRAMPOLINE: usize = 0x6000_1000;

core/src/config/loongarch64.rs

@@ -14,10 +14,12 @@ pub const USER_STACK_SIZE: usize = 0x8_0000;
 /// The lowest address of the user heap.
 pub const USER_HEAP_BASE: usize = 0x4000_0000;
 /// The size of the user heap.
-pub const USER_HEAP_SIZE: usize = 0x1_0000;
+pub const USER_HEAP_SIZE: usize = 0x1_0000;  // 64KB
+/// The maximum size of the user heap (for brk expansion).
+pub const USER_HEAP_SIZE_MAX: usize = 0x2000_0000;  // 512MB
 
 /// The base address for user interpreter.
 pub const USER_INTERP_BASE: usize = 0x400_0000;
 
-/// The address of signal trampoline.
-pub const SIGNAL_TRAMPOLINE: usize = 0x4001_0000;
+/// The address of signal trampoline (placed at top of user heap).
+pub const SIGNAL_TRAMPOLINE: usize = 0x6000_1000;

core/src/config/riscv64.rs

@@ -15,9 +15,11 @@ pub const USER_STACK_SIZE: usize = 0x8_0000;
 pub const USER_HEAP_BASE: usize = 0x4000_0000;
 /// The size of the user heap.
 pub const USER_HEAP_SIZE: usize = 0x1_0000;
+/// The maximum size of the user heap (for brk expansion).
+pub const USER_HEAP_SIZE_MAX: usize = 0x2000_0000;
 
 /// The base address for user interpreter.
 pub const USER_INTERP_BASE: usize = 0x400_0000;
 
-/// The address of signal trampoline.
-pub const SIGNAL_TRAMPOLINE: usize = 0x4001_0000;
+/// The address of signal trampoline (placed at top of user heap).
+pub const SIGNAL_TRAMPOLINE: usize = 0x6000_1000;

core/src/config/x86_64.rs

@@ -15,9 +15,11 @@ pub const USER_STACK_SIZE: usize = 0x8_0000;
 pub const USER_HEAP_BASE: usize = 0x4000_0000;
 /// The size of the user heap.
 pub const USER_HEAP_SIZE: usize = 0x1_0000;
+/// The maximum size of the user heap (for brk expansion).
+pub const USER_HEAP_SIZE_MAX: usize = 0x2000_0000;
 
 /// The base address for user interpreter.
 pub const USER_INTERP_BASE: usize = 0x400_0000;
 
-/// The address of signal trampoline.
-pub const SIGNAL_TRAMPOLINE: usize = 0x4001_0000;
+/// The address of signal trampoline (placed at top of user heap).
+pub const SIGNAL_TRAMPOLINE: usize = 0x6000_1000;