Framebuffer configuration

README.md

@@ -60,7 +60,6 @@ The purposes of the individual assembly stages in this project are the following
 
 ## Future Plans
 
-- [ ] Allow to configure the desired screen resolution. Right now we just use the first available VESA screen mode on BIOS and the default GOP mode on UEFI.
 - [ ] Create a `multiboot2` compatible disk image in addition to the BIOS and UEFI disk images. This would make it possible to use it on top of the GRUB bootloader.
 - [ ] Rewrite most of the BIOS assembly stages in Rust. This has already started.
 - [ ] Instead of linking the kernel bytes directly with the bootloader, use a filesystem (e.g. FAT) and load the kernel as a separate file.

build.rs

@@ -201,7 +201,8 @@ mod binary {
         }
 
         // Parse configuration from the kernel's Cargo.toml
-        let config = match env::var("KERNEL_MANIFEST") {
+        let mut config = None;
+        let config_stream = match env::var("KERNEL_MANIFEST") {
             Err(env::VarError::NotPresent) => {
                 panic!("The KERNEL_MANIFEST environment variable must be set for building the bootloader.\n\n\
                  Please use `cargo builder` for building.");
@@ -260,10 +261,14 @@ mod binary {
                         .cloned()
                         .unwrap_or_else(|| toml::Value::Table(toml::map::Map::new()));
 
-                    config_table
-                        .try_into::<ParsedConfig>()
-                        .map(|c| quote! { #c })
-                        .unwrap_or_else(|err| {
+                    let result = config_table.try_into::<ParsedConfig>();
+                    match result {
+                        Ok(p_config) => {
+                            let stream = quote! { #p_config };
+                            config = Some(p_config);
+                            stream
+                        }
+                        Err(err) => {
                             let err = format!(
                                 "failed to parse bootloader config in {}:\n\n{}",
                                 path,
@@ -272,7 +277,8 @@ mod binary {
                             quote! {
                                 compile_error!(#err)
                             }
-                        })
+                        }
+                    }
                 } else {
                     let err = format!(
                         "no bootloader dependency in {}\n\n  The \
@@ -286,21 +292,44 @@ mod binary {
                 }
             }
         };
+        let config = config;
 
         // Write config to file
         let file_path = out_dir.join("bootloader_config.rs");
-        let mut file = File::create(file_path).expect("failed to create bootloader_config.rs");
+        let mut file = File::create(file_path).expect("failed to create config file");
         file.write_all(
             quote::quote! {
-                mod parsed_config {
+                /// Module containing the user-supplied configuration.
+                /// Public so that `bin/uefi.rs` can read framebuffer configuration.
+                pub mod parsed_config {
                     use crate::config::Config;
-                    pub const CONFIG: Config = #config;
+                    /// The parsed configuration given by the user.
+                    pub const CONFIG: Config = #config_stream;
                 }
             }
             .to_string()
             .as_bytes(),
         )
-        .expect("write to bootloader_config.rs failed");
+        .expect("writing config failed");
+
+        // Write VESA framebuffer configuration
+        let file_path = out_dir.join("vesa_config.s");
+        let mut file = File::create(file_path).expect("failed to create vesa config file");
+        file.write_fmt(format_args!(
+            "vesa_minx: .2byte {}\n\
+            vesa_miny: .2byte {}",
+            config
+                .as_ref()
+                .map(|c| c.minimum_framebuffer_width)
+                .flatten()
+                .unwrap_or(640),
+            config
+                .as_ref()
+                .map(|c| c.minimum_framebuffer_height)
+                .flatten()
+                .unwrap_or(480)
+        ))
+        .expect("writing config failed");
 
         println!("cargo:rerun-if-env-changed=KERNEL");
         println!("cargo:rerun-if-env-changed=KERNEL_MANIFEST");
@@ -333,6 +362,8 @@ mod binary {
         pub kernel_stack_address: Option<AlignedAddress>,
         pub boot_info_address: Option<AlignedAddress>,
         pub framebuffer_address: Option<AlignedAddress>,
+        pub minimum_framebuffer_height: Option<usize>,
+        pub minimum_framebuffer_width: Option<usize>,
     }
 
     /// Convert to tokens suitable for initializing the `Config` struct.
@@ -351,6 +382,8 @@ mod binary {
             let kernel_stack_address = optional(self.kernel_stack_address);
             let boot_info_address = optional(self.boot_info_address);
             let framebuffer_address = optional(self.framebuffer_address);
+            let minimum_framebuffer_height = optional(self.minimum_framebuffer_height);
+            let minimum_framebuffer_width = optional(self.minimum_framebuffer_width);
 
             tokens.extend(quote! { Config {
                 map_physical_memory: #map_physical_memory,
@@ -362,6 +395,8 @@ mod binary {
                 kernel_stack_address: #kernel_stack_address,
                 boot_info_address: #boot_info_address,
                 framebuffer_address: #framebuffer_address,
+                minimum_framebuffer_height: #minimum_framebuffer_height,
+                minimum_framebuffer_width: #minimum_framebuffer_width
             }});
         }
     }

src/asm/vesa.s

@@ -124,9 +124,6 @@ vesa_returngood:
     xor eax, eax
     ret
 
-vesa_minx: .2byte 640
-vesa_miny: .2byte 480
-
 vesa_modeok:
     .ascii ": Is this OK? (s)ave/(y)es/(n)o    "
     .byte 8,8,8,8,0

src/bin/bios.rs

@@ -22,6 +22,7 @@ use x86_64::{PhysAddr, VirtAddr};
 
 global_asm!(include_str!("../asm/stage_1.s"));
 global_asm!(include_str!("../asm/stage_2.s"));
+global_asm!(include_str!(concat!(env!("OUT_DIR"), "/vesa_config.s")));
 global_asm!(include_str!("../asm/vesa.s"));
 global_asm!(include_str!("../asm/e820.s"));
 global_asm!(include_str!("../asm/stage_3.s"));

src/bin/uefi.rs

@@ -14,14 +14,15 @@ static KERNEL: PageAligned<[u8; KERNEL_SIZE]> = PageAligned(KERNEL_BYTES);
 struct PageAligned<T>(T);
 
 use bootloader::{
-    binary::{legacy_memory_region::LegacyFrameAllocator, SystemInfo},
+    binary::{legacy_memory_region::LegacyFrameAllocator, parsed_config::CONFIG, SystemInfo},
     boot_info::FrameBufferInfo,
 };
 use core::{mem, panic::PanicInfo, slice};
 use uefi::{
     prelude::{entry, Boot, Handle, ResultExt, Status, SystemTable},
     proto::console::gop::{GraphicsOutput, PixelFormat},
     table::boot::{MemoryDescriptor, MemoryType},
+    Completion,
 };
 use x86_64::{
     structures::paging::{FrameAllocator, OffsetPageTable, PageTable, PhysFrame, Size4KiB},
@@ -149,6 +150,28 @@ fn init_logger(st: &SystemTable<Boot>) -> (PhysAddr, FrameBufferInfo) {
         .expect_success("failed to locate gop");
     let gop = unsafe { &mut *gop.get() };
 
+    let mode = {
+        let modes = gop.modes().map(Completion::unwrap);
+        match (
+            CONFIG.minimum_framebuffer_height,
+            CONFIG.minimum_framebuffer_width,
+        ) {
+            (Some(height), Some(width)) => modes
+                .filter(|m| {
+                    let res = m.info().resolution();
+                    res.1 >= height && res.0 >= width
+                })
+                .last(),
+            (Some(height), None) => modes.filter(|m| m.info().resolution().1 >= height).last(),
+            (None, Some(width)) => modes.filter(|m| m.info().resolution().0 >= width).last(),
+            _ => None,
+        }
+    };
+    if let Some(mode) = mode {
+        gop.set_mode(&mode)
+            .expect_success("Failed to apply the desired display mode");
+    }
+
     let mode_info = gop.current_mode_info();
     let mut framebuffer = gop.frame_buffer();
     let slice = unsafe { slice::from_raw_parts_mut(framebuffer.as_mut_ptr(), framebuffer.size()) };

src/config.rs

@@ -75,4 +75,16 @@ pub struct Config {
     ///
     /// Only considered if `map_framebuffer` is `true`.
     pub framebuffer_address: Option<u64>,
+    /// Desired minimum height of the framebuffer mode.
+    ///
+    /// Defaults to using the default mode if neither `minimum_framebuffer_height` or
+    /// `minimum_framebuffer_width` is supplied, and using the last available mode that
+    /// fits them if 1 or more is set.
+    pub minimum_framebuffer_height: Option<usize>,
+    /// Desired minimum width of the framebuffer mode.
+    ///
+    /// Defaults to using the default mode if neither `minimum_framebuffer_height` or
+    /// `minimum_framebuffer_width` is supplied, and using the last available mode that
+    /// fits them if 1 or more is set.
+    pub minimum_framebuffer_width: Option<usize>,
 }