multiboot2: Rework boxed_dst_tag

Passing a size was not a good idea as it can be inferred from the slice.

Author: YtvwlD

multiboot2/src/boot_loader_name.rs

@@ -36,10 +36,8 @@ impl BootLoaderNameTag {
         // allocate a C string
         let cstr = CString::new(name)
             .expect("failed to create CString");
-        let bytes = cstr.to_bytes_with_nul();
-        let size = (bytes.len() + METADATA_SIZE).try_into().unwrap();
         let tag = boxed_dst_tag(
-            TagType::BootLoaderName, size, Some(cstr.as_bytes_with_nul())
+            TagType::BootLoaderName, cstr.as_bytes_with_nul(),
         );
         unsafe { Box::from_raw(Box::into_raw(tag) as *mut Self) }
     }

multiboot2/src/builder/mod.rs

@@ -14,30 +14,26 @@ use alloc::boxed::Box;
 
 use crate::{TagType, Tag};
 
-/// Create a boxed tag with the given size. This includes type and size.
-pub(super) fn boxed_dst_tag(
-    typ: TagType, size: u32, content: Option<&[u8]>
-) -> Box<Tag> {
+/// Create a boxed tag with the given content.
+pub(super) fn boxed_dst_tag(typ: TagType, content: &[u8]) -> Box<Tag> {
     // based on https://stackoverflow.com/a/64121094/2192464
     let (layout, size_offset) = Layout::new::<TagType>()
         .extend(Layout::new::<u32>()).unwrap();
     let (layout, inner_offset) = layout.extend(
-        Layout::array::<usize>(
-            size as usize - size_of::<TagType>() - size_of::<u32>()
-        ).unwrap()
+        Layout::array::<usize>(content.len()).unwrap()
     ).unwrap();
     let ptr = unsafe { alloc(layout) };
     assert!(!ptr.is_null());
     unsafe {
         // initialize the content as good as we can
         ptr.cast::<TagType>().write(typ);
-        ptr.add(size_offset).cast::<u32>().write(size);
+        ptr.add(size_offset).cast::<u32>().write((
+            content.len() + size_of::<TagType>() + size_of::<u32>()
+        ).try_into().unwrap());
         // initialize body
-        if let Some(c) = content {
-            let content_ptr = ptr.add(inner_offset);
-            for (idx, val) in c.iter().enumerate() {
-                content_ptr.add(idx).write(*val);
-            }
+        let content_ptr = ptr.add(inner_offset);
+        for (idx, val) in content.iter().enumerate() {
+            content_ptr.add(idx).write(*val);
         }
         Box::from_raw(
             core::ptr::from_raw_parts_mut(

multiboot2/src/command_line.rs

@@ -37,9 +37,7 @@ impl CommandLineTag {
         // allocate a C string
         let cstr = CString::new(command_line)
             .expect("failed to create CString");
-        let bytes = cstr.to_bytes_with_nul();
-        let size = (bytes.len() + METADATA_SIZE).try_into().unwrap();
-        let tag = boxed_dst_tag(TagType::Cmdline, size, Some(cstr.as_bytes_with_nul()));
+        let tag = boxed_dst_tag(TagType::Cmdline, cstr.as_bytes_with_nul());
         unsafe { Box::from_raw(Box::into_raw(tag) as *mut Self) }
     }
 

multiboot2/src/elf_sections.rs

@@ -1,16 +1,14 @@
-use crate::tag_type::{Tag, TagType};
+use crate::tag_type::TagType;
 #[cfg(feature = "builder")]
 use crate::builder::boxed_dst_tag;
 #[cfg(feature = "builder")]
 use crate::builder::traits::StructAsBytes;
 
 use core::convert::TryInto;
-use core::{fmt::{Debug, Formatter}, mem};
+use core::fmt::{Debug, Formatter};
 #[cfg(feature = "builder")]
 use alloc::boxed::Box;
 
-const METADATA_SIZE: usize = mem::size_of::<TagType>() + mem::size_of::<u32>();
-
 /// This tag contains section header table from an ELF kernel.
 ///
 /// The sections iterator is provided via the `sections` method.
@@ -28,15 +26,12 @@ pub struct ElfSectionsTag {
 impl ElfSectionsTag {
     #[cfg(feature = "builder")]
     pub fn new(number_of_sections: u32, entry_size: u32, shndx: u32, sections: &[u8]) -> Box<Self> {
-        let size = (sections.len() + METADATA_SIZE).try_into().unwrap();
         let mut bytes = [
             number_of_sections.to_le_bytes(), entry_size.to_le_bytes(),
             shndx.to_le_bytes(),
         ].concat();
         bytes.extend_from_slice(sections);
-        let tag = boxed_dst_tag(
-            TagType::ElfSections, size, Some(bytes.as_slice())
-        );
+        let tag = boxed_dst_tag(TagType::ElfSections, bytes.as_slice());
         unsafe { Box::from_raw(Box::into_raw(tag) as *mut Self) }
     }
 

multiboot2/src/framebuffer.rs

@@ -62,10 +62,7 @@ impl FramebufferTag {
         bytes.extend(bpp.to_le_bytes());
         bytes.extend(buffer_type.to_bytes());
 
-        let size = (bytes.len() + METADATA_SIZE).try_into().unwrap();
-        let tag = boxed_dst_tag(
-            TagType::Framebuffer, size, Some(&bytes)
-        );
+        let tag = boxed_dst_tag(TagType::Framebuffer, &bytes);
         unsafe { Box::from_raw(Box::into_raw(tag) as *mut Self) }
     }
 

multiboot2/src/memory_map.rs

@@ -42,10 +42,7 @@ impl MemoryMapTag {
         for area in areas {
             bytes.extend(area.struct_as_bytes());
         }
-        let tag = boxed_dst_tag(
-            TagType::Mmap, bytes.len().try_into().unwrap(),
-            Some(bytes.as_slice()),
-        );
+        let tag = boxed_dst_tag(TagType::Mmap, bytes.as_slice());
         unsafe { Box::from_raw(Box::into_raw(tag) as *mut Self) }
     }
 

multiboot2/src/module.rs

@@ -37,13 +37,11 @@ impl ModuleTag {
 
         let cstr = CString::new(cmdline)
             .expect("failed to create CString");
-        let bytes = cstr.to_bytes_with_nul();
-        let size = (bytes.len() + METADATA_SIZE).try_into().unwrap();
         let start_bytes = start.to_le_bytes();
         let end_bytes = end.to_le_bytes();
         let mut content_bytes = [start_bytes, end_bytes].concat();
         content_bytes.extend_from_slice(cstr.as_bytes_with_nul());
-        let tag = boxed_dst_tag(TagType::Module, size, Some(content_bytes.as_slice()));
+        let tag = boxed_dst_tag(TagType::Module, content_bytes.as_slice());
         unsafe { Box::from_raw(Box::into_raw(tag) as *mut Self) }
     }