speedup loading

src/main.zig

@@ -173,14 +173,13 @@ fn loadStaticElf(ehdr: elf.Header, file_reader: *std.fs.File.Reader) !usize {
     const base = try posix.mmap(
         hint,
         maxva - minva,
-        posix.PROT.NONE,
+        posix.PROT.WRITE,
         .{ .TYPE = .PRIVATE, .ANONYMOUS = true, .FIXED_NOREPLACE = !dynamic },
         -1,
         0,
     );
     log.debug("Pre-flight reservation at: {*}, size: 0x{x}", .{ base.ptr, base.len });
 
-    const flags = posix.MAP{ .TYPE = .PRIVATE, .ANONYMOUS = true, .FIXED = true };
     var phdrs = ehdr.iterateProgramHeaders(file_reader);
     var phdr_idx: u32 = 0;
     errdefer posix.munmap(base);
@@ -197,17 +196,7 @@ fn loadStaticElf(ehdr: elf.Header, file_reader: *std.fs.File.Reader) !usize {
             "  - phdr[{}]: mapping 0x{x} - 0x{x} (vaddr=0x{x}, dyn_base=0x{x})",
             .{ phdr_idx, start, start + size, phdr.p_vaddr, base_for_dyn },
         );
-        // NOTE: We can't use a single file-backed mmap for the segment, because p_memsz may be
-        // larger than p_filesz. This difference accounts for the .bss section, which must be
-        // zero-initialized.
-        const ptr = try posix.mmap(
-            @as(?[*]align(page_size) u8, @ptrFromInt(start)),
-            size,
-            posix.PROT.WRITE,
-            flags,
-            -1,
-            0,
-        );
+        const ptr: []align(page_size) u8 = @as([*]align(page_size) u8, @ptrFromInt(start))[0..size];
         try file_reader.seekTo(phdr.p_offset);
         if (try file_reader.read(ptr[offset..][0..phdr.p_filesz]) != phdr.p_filesz)
             return UnfinishedReadError.UnfinishedRead;