Merge pull request #96 from rust-osdev/elf-tls-sections

Add basic support for ELF thread local storage segments

Author: phil-opp

Diff for: src/bootinfo/mod.rs

@@ -42,6 +42,7 @@ pub struct BootInfo {
     /// can be safely accessed.
     #[cfg(feature = "map_physical_memory")]
     pub physical_memory_offset: u64,
+    tls_template: TlsTemplate,
     _non_exhaustive: u8, // `()` is not FFI safe
 }
 
@@ -51,18 +52,61 @@ impl BootInfo {
     #[doc(hidden)]
     pub fn new(
         memory_map: MemoryMap,
+        tls_template: Option<TlsTemplate>,
         recursive_page_table_addr: u64,
         physical_memory_offset: u64,
     ) -> Self {
+        let tls_template = tls_template.unwrap_or(TlsTemplate {
+            start_addr: 0,
+            file_size: 0,
+            mem_size: 0,
+        });
         BootInfo {
             memory_map,
+            tls_template,
             #[cfg(feature = "recursive_page_table")]
             recursive_page_table_addr,
             #[cfg(feature = "map_physical_memory")]
             physical_memory_offset,
             _non_exhaustive: 0,
         }
     }
+
+    /// Returns information about the thread local storage segment of the kernel.
+    ///
+    /// Returns `None` if the kernel has no thread local storage segment.
+    ///
+    /// (The reason this is a method instead of a normal field is that `Option`
+    /// is not FFI-safe.)
+    pub fn tls_template(&self) -> Option<TlsTemplate> {
+        if self.tls_template.mem_size > 0 {
+            Some(self.tls_template)
+        } else {
+            None
+        }
+    }
+}
+
+/// Information about the thread local storage (TLS) template.
+///
+/// This template can be used to set up thread local storage for threads. For
+/// each thread, a new memory location of size `mem_size` must be initialized.
+/// Then the first `file_size` bytes of this template needs to be copied to the
+/// location. The additional `mem_size - file_size` bytes must be initialized with
+/// zero.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(C)]
+pub struct TlsTemplate {
+    /// The virtual start address of the thread local storage template.
+    pub start_addr: u64,
+    /// The number of data bytes in the template.
+    ///
+    /// Corresponds to the length of the `.tdata` section.
+    pub file_size: u64,
+    /// The total number of bytes that the TLS segment should have in memory.
+    ///
+    /// Corresponds to the combined length of the `.tdata` and `.tbss` sections.
+    pub mem_size: u64,
 }
 
 extern "C" {

Diff for: src/main.rs

@@ -271,7 +271,7 @@ fn bootloader_main(
     };
 
     // Map kernel segments.
-    let stack_end = page_table::map_kernel(
+    let kernel_memory_info = page_table::map_kernel(
         kernel_start.phys(),
         kernel_stack_address,
         KERNEL_STACK_SIZE,
@@ -324,6 +324,7 @@ fn bootloader_main(
     // Construct boot info structure.
     let mut boot_info = BootInfo::new(
         memory_map,
+        kernel_memory_info.tls_segment,
         recursive_page_table_addr.as_u64(),
         physical_memory_offset,
     );
@@ -352,7 +353,7 @@ fn bootloader_main(
     sse::enable_sse();
 
     let entry_point = VirtAddr::new(entry_point);
-    unsafe { context_switch(boot_info_addr, entry_point, stack_end) };
+    unsafe { context_switch(boot_info_addr, entry_point, kernel_memory_info.stack_end) };
 }
 
 fn enable_nxe_bit() {

Diff for: src/page_table.rs

@@ -1,5 +1,6 @@
 use crate::frame_allocator::FrameAllocator;
 use bootloader::bootinfo::MemoryRegionType;
+use bootloader::bootinfo::TlsTemplate;
 use fixedvec::FixedVec;
 use x86_64::structures::paging::mapper::{MapToError, MapperFlush, UnmapError};
 use x86_64::structures::paging::{
@@ -9,16 +10,40 @@ use x86_64::structures::paging::{
 use x86_64::{align_up, PhysAddr, VirtAddr};
 use xmas_elf::program::{self, ProgramHeader64};
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct MemoryInfo {
+    pub stack_end: VirtAddr,
+    pub tls_segment: Option<TlsTemplate>,
+}
+
+#[derive(Debug)]
+pub enum MapKernelError {
+    Mapping(MapToError),
+    MultipleTlsSegments,
+}
+
+impl From<MapToError> for MapKernelError {
+    fn from(e: MapToError) -> Self {
+        MapKernelError::Mapping(e)
+    }
+}
+
 pub(crate) fn map_kernel(
     kernel_start: PhysAddr,
     stack_start: Page,
     stack_size: u64,
     segments: &FixedVec<ProgramHeader64>,
     page_table: &mut RecursivePageTable,
     frame_allocator: &mut FrameAllocator,
-) -> Result<VirtAddr, MapToError> {
+) -> Result<MemoryInfo, MapKernelError> {
+    let mut tls_segment = None;
     for segment in segments {
-        map_segment(segment, kernel_start, page_table, frame_allocator)?;
+        let tls = map_segment(segment, kernel_start, page_table, frame_allocator)?;
+        if let Some(tls) = tls {
+            if tls_segment.replace(tls).is_some() {
+                return Err(MapKernelError::MultipleTlsSegments);
+            }
+        }
     }
 
     // Create a stack
@@ -35,15 +60,18 @@ pub(crate) fn map_kernel(
         unsafe { map_page(page, frame, flags, page_table, frame_allocator)? }.flush();
     }
 
-    Ok(stack_end.start_address())
+    Ok(MemoryInfo {
+        stack_end: stack_end.start_address(),
+        tls_segment,
+    })
 }
 
 pub(crate) fn map_segment(
     segment: &ProgramHeader64,
     kernel_start: PhysAddr,
     page_table: &mut RecursivePageTable,
     frame_allocator: &mut FrameAllocator,
-) -> Result<(), MapToError> {
+) -> Result<Option<TlsTemplate>, MapToError> {
     let typ = segment.get_type().unwrap();
     match typ {
         program::Type::Load => {
@@ -160,10 +188,16 @@ pub(crate) fn map_segment(
                     unsafe { addr.as_mut_ptr::<u8>().write(0) };
                 }
             }
+
+            Ok(None)
         }
-        _ => {}
+        program::Type::Tls => Ok(Some(TlsTemplate {
+            start_addr: segment.virtual_addr,
+            mem_size: segment.mem_size,
+            file_size: segment.file_size,
+        })),
+        _ => Ok(None),
     }
-    Ok(())
 }
 
 pub(crate) unsafe fn map_page<'a, S>(