fixed brk syscall

Author: lukasx999

src/memory.hh

@@ -52,13 +52,9 @@ public:
     }
 
     [[nodiscard]] void* get_initial_program_break() const {
+        // TODO: align to next page
         auto& [addr, len] = m_mapped_segments.back();
-        size_t program_break = reinterpret_cast<size_t>(addr) + len;
-        // set the program break to the next full page, to avoid address collisions with the
-        // previous page from the data segment
-        // TODO: dont jump to the next page if program_break is perfectly page aligned
-        size_t aligned = align_to_page_size(program_break) + getpagesize();
-        return reinterpret_cast<void*>(aligned);
+        return reinterpret_cast<char*>(addr) + len;
     }
 
 private:

src/probe/test.c

@@ -34,12 +34,24 @@ void dynarray_push_back(DynamicArray *dynarray, Item item) {
 
 int main(void) {
 
-    int *mem = malloc(20);
-    if (mem == NULL)
-        printf("is null\n");
-
-    // DynamicArray dynarray = {0};
-    // dynarray_init(&dynarray);
-    // dynarray_push_back(&dynarray, 1);
+    // int *mem = malloc(20);
+    // if (mem == NULL)
+    //     printf("is null\n");
+
+    DynamicArray dynarray = {0};
+    dynarray_init(&dynarray);
+    dynarray_push_back(&dynarray, 1);
+    dynarray_push_back(&dynarray, 2);
+    dynarray_push_back(&dynarray, 3);
+    dynarray_push_back(&dynarray, 4);
+    dynarray_push_back(&dynarray, 5);
+    dynarray_push_back(&dynarray, 6);
+    dynarray_push_back(&dynarray, 7);
+    dynarray_push_back(&dynarray, 8);
+    dynarray_push_back(&dynarray, 9);
+
+    for (size_t i=0; i < dynarray.length; ++i) {
+        printf("%d\n", dynarray.items[i]);
+    }
 
 }

src/syscalls.hh

@@ -32,16 +32,15 @@ SYSCALL_NODISCARD inline int close(int fd) {
     }
 }
 
-// TODO: doesnt quite work yet
 SYSCALL_NODISCARD inline Word brk(CPU& cpu, Word new_brk) {
 
-    std::println("new brk: {:#x}", new_brk);
-
+    // TODO: create a util.hh wrapper for aligning to the NEXT page boundary
     auto new_addr = reinterpret_cast<void*>(align_to_page_size(new_brk)+getpagesize());
     auto old_addr = reinterpret_cast<void*>(align_to_page_size(reinterpret_cast<size_t>(cpu.get_program_break()))+getpagesize());
 
     // brk() syscall differs from the libc wrapper, in that it returns
     // the current program break when calling it with NULL
+    // `man 2 brk` documents the libc wrapper, not the raw syscall!
     if (new_brk == 0)
         return reinterpret_cast<Word>(old_addr);
 
@@ -50,7 +49,8 @@ SYSCALL_NODISCARD inline Word brk(CPU& cpu, Word new_brk) {
 
         ptrdiff_t size = static_cast<char*>(new_addr) - static_cast<char*>(old_addr);
 
-        auto ret = ::mmap(
+        // TODO: handle mmap() failure
+        [[gnu::unused]] void* unused_ret = mmap(
             old_addr,
             size,
             PROT_WRITE | PROT_READ,
@@ -59,13 +59,10 @@ SYSCALL_NODISCARD inline Word brk(CPU& cpu, Word new_brk) {
             0
         );
 
-        if (ret == MAP_FAILED) {
-            return -1;
-        }
-
         cpu.set_program_break(new_addr);
 
     } else if (new_addr < old_addr) {
+        // TODO:
         // shrink the heap
 
         // ptrdiff_t size = static_cast<char*>(old_addr) - static_cast<char*>(new_addr);
@@ -76,12 +73,9 @@ SYSCALL_NODISCARD inline Word brk(CPU& cpu, Word new_brk) {
         //     return -1;
         // }
 
-    } else if (new_addr == old_addr) {
-        // do nothing
-
     }
 
-    return 0;
+    return new_brk;
 }
 
 } // namespace syscalls

src/util.hh

@@ -34,7 +34,7 @@ void log(std::format_string<Args...> fmt, Args&& ...args) {
     std::println(stderr, fmt, std::forward<Args>(args)...);
 }
 
-[[nodiscard]] inline size_t align_to_page_size(size_t address) {
+[[nodiscard]] constexpr inline size_t align_to_page_size(size_t address) {
     return address - address % getpagesize();
 }