[kernel] Hide kernel symbols by default

Using `-fvisibility=hidden` when building the kernel, and then
`--discard-all` when stripping it, we shave almost 100KiB off of the
resulting ELF file.

Also dropped some unused symbols from the linker script, and rearranged
the sections so that the file is able to be mapped directly into memory
instead of having each section copied.

configs/kernel-debug.yaml

@@ -15,11 +15,14 @@ variables:
     "-ffreestanding",
     "-nodefaultlibs",
     "-fno-builtin",
+    "-fno-plt",
 
     "-mno-sse",
     "-fno-omit-frame-pointer",
     "-mno-red-zone",
     "-mcmodel=kernel",
+    "-fvisibility=hidden",
+    "-fvisibility-inlines-hidden",
 
     "-g3",
     "-ggdb",

configs/rules.ninja

@@ -75,7 +75,7 @@ rule strip
     command = $
         cp $in $out; $
         objcopy --only-keep-debug $out $debug; $
-        strip -g $out; $
+        strip --discard-all -g $out; $
         objcopy --add-gnu-debuglink=$debug $out
 
 rule touch

external/uefi/boot_services.h

@@ -22,7 +22,7 @@ namespace bs_impl {
 	using create_event = status (*)(evt, tpl, event_notify, void*, event*);
 	using exit_boot_services = status (*)(handle, size_t);
 	using locate_protocol = status (*)(const guid*, void*, void**);
-	using copy_mem = void (*)(void*, void*, size_t);
+	using copy_mem = void (*)(void*, const void*, size_t);
 	using set_mem = void (*)(void*, uint64_t, uint8_t);
 }
 

src/boot/allocator.cpp

@@ -155,7 +155,7 @@ allocator::memset(void *start, size_t size, uint8_t value)
 }
 
 void
-allocator::copy(void *to, void *from, size_t size)
+allocator::copy(void *to, const void *from, size_t size)
 {
     m_bs.copy_mem(to, from, size);
 }

src/boot/allocator.h

@@ -35,7 +35,7 @@ public:
     module * allocate_module();
 
     void memset(void *start, size_t size, uint8_t value);
-    void copy(void *to, void *from, size_t size);
+    void copy(void *to, const void *from, size_t size);
 
     inline void zero(void *start, size_t size) { memset(start, size, 0); }
 

src/boot/loader.cpp

@@ -35,15 +35,42 @@ load_file(
     return b;
 }
 
+void
+verify_kernel_header(elf::file &kernel, util::const_buffer data)
+{
+    status_line status {L"Verifying kernel header"};
+
+    // The header should be the first non-null section
+    const elf::section_header &sect = kernel.sections()[1];
+
+    const bootproto::header *header =
+        reinterpret_cast<const bootproto::header *>(
+            util::offset_pointer(data.pointer, sect.offset));
+
+    if (header->magic != bootproto::header_magic)
+        error::raise(uefi::status::load_error, L"Bad kernel magic number");
+
+    if (header->length < sizeof(bootproto::header))
+        error::raise(uefi::status::load_error, L"Bad kernel header length");
+
+    if (header->version < bootproto::min_header_version)
+        error::raise(uefi::status::unsupported, L"Kernel header version not supported");
+
+    console::print(L"    Loaded kernel vserion: %d.%d.%d %x\r\n",
+            header->version_major, header->version_minor, header->version_patch,
+            header->version_gitsha);
+}
+
 bootproto::program *
 load_program(
     fs::file &disk,
     const wchar_t *name,
-    const descriptor &desc)
+    const descriptor &desc,
+    bool verify)
 {
     status_line status(L"Loading program", name);
 
-    util::buffer data = load_file(disk, desc.path);
+    util::const_buffer data = load_file(disk, desc.path);
 
     elf::file program(data.pointer, data.count);
     if (!program.valid()) {
@@ -60,6 +87,9 @@ load_program(
         error::raise(uefi::status::load_error, L"ELF file not valid");
     }
 
+    if (verify)
+        verify_kernel_header(program, data);
+
     size_t num_sections = 0;
     for (auto &seg : program.programs()) {
         if (seg.type == elf::segment_type::load)
@@ -85,7 +115,7 @@ load_program(
 
         size_t page_count = memory::bytes_to_pages(mem_size);
         void *pages = g_alloc.allocate_pages(page_count, alloc_type::program, true);
-        void *source = util::offset_pointer(data.pointer, seg.offset);
+        const void *source = util::offset_pointer(data.pointer, seg.offset);
         g_alloc.copy(util::offset_pointer(pages, prelude), source, seg.file_size);
         section.phys_addr = reinterpret_cast<uintptr_t>(pages);
         section.virt_addr = virt_addr;
@@ -116,33 +146,5 @@ load_module(
     mod->data = load_file(disk, path);
 }
 
-void
-verify_kernel_header(bootproto::program &program)
-{
-    status_line status(L"Verifying kernel header");
-
-    const bootproto::header *header =
-        reinterpret_cast<const bootproto::header *>(program.sections[0].phys_addr);
-
-    if (header->magic != bootproto::header_magic)
-        error::raise(uefi::status::load_error, L"Bad kernel magic number");
-
-    if (header->length < sizeof(bootproto::header))
-        error::raise(uefi::status::load_error, L"Bad kernel header length");
-
-    if (header->version < bootproto::min_header_version)
-        error::raise(uefi::status::unsupported, L"Kernel header version not supported");
-
-    console::print(L"    Loaded kernel vserion: %d.%d.%d %x\r\n",
-            header->version_major, header->version_minor, header->version_patch,
-            header->version_gitsha);
-
-    /*
-    for (auto &section : program.sections)
-        console::print(L"    Section: p:0x%lx v:0x%lx fs:0x%x ms:0x%x\r\n",
-            section.phys_addr, section.virt_addr, section.file_size, section.mem_size);
-    */
-}
-
 } // namespace loader
 } // namespace boot

src/boot/loader.h

@@ -31,11 +31,13 @@ load_file(
 /// \arg disk   The opened UEFI filesystem to load from
 /// \arg desc   The descriptor identifying the program
 /// \arg name   The human-readable name of the program to load
+/// \arg verify If this is the kernel and should have its header verified
 bootproto::program *
 load_program(
     fs::file &disk,
     const wchar_t *name,
-    const descriptor &desc);
+    const descriptor &desc,
+    bool verify = false);
 
 /// Load a file from disk into memory, creating an init args module
 /// \arg disk    The opened UEFI filesystem to load from
@@ -51,10 +53,5 @@ load_module(
     bootproto::module_type type,
     uint16_t subtype);
 
-/// Verify that a loaded ELF has the j6 kernel header
-/// \arg program  The program to check for a header
-void
-verify_kernel_header(bootproto::program &program);
-
 } // namespace loader
 } // namespace boot

src/boot/main.cpp

@@ -75,7 +75,7 @@ load_resources(bootproto::args *args, video::screen *screen, uefi::handle image,
     fs::file bc_data = disk.open(L"jsix\\boot.conf");
     bootconfig bc {bc_data.load(), bs};
 
-    args->kernel = loader::load_program(disk, L"kernel", bc.kernel());
+    args->kernel = loader::load_program(disk, L"kernel", bc.kernel(), true);
     args->init = loader::load_program(disk, L"init server", bc.init());
     args->flags = static_cast<bootproto::boot_flags>(bc.flags());
 
@@ -106,8 +106,6 @@ load_resources(bootproto::args *args, video::screen *screen, uefi::handle image,
             }
         }
     }
-
-    loader::verify_kernel_header(*args->kernel);
 }
 
 memory::efi_mem_map

src/kernel/boot.s

@@ -2,7 +2,7 @@ MAGIC	equ  'j6KERNEL'	; jsix kernel header magic number
 
 section .header
 align 8
-global _kernel_header
+global _kernel_header: data hidden
 _kernel_header:
 	dq MAGIC            ; Kernel header magic
 	dw 32               ; Kernel header length
@@ -16,8 +16,8 @@ _kernel_header:
 
 section .text
 align 16
-global _kernel_start:function (_kernel_start.end - _kernel_start)
+global _kernel_start: function hidden (_kernel_start.end - _kernel_start)
-global _kernel_start.real
+global _kernel_start.real: function hidden
 _kernel_start:
 	push rbp     ; Never executed, fake function prelude
 	mov rbp, rsp ; to calm down gdb
@@ -36,18 +36,18 @@ _kernel_start:
     ; the scheduler to take over
 .end:
 
-global bsp_idle:function (bsp_idle.end - bsp_idle)
+global bsp_idle: function hidden (bsp_idle.end - bsp_idle)
 bsp_idle:
 	hlt
 	jmp bsp_idle
 .end:
 
-global interrupts_enable
+global interrupts_enable: function hidden
 interrupts_enable:
 	sti
 	ret
 
-global interrupts_disable
+global interrupts_disable: function hidden
 interrupts_disable:
 	cli
 	ret
@@ -57,5 +57,5 @@ align 0x100
 idle_stack_begin:
 	resb 0x4000 ; 16KiB stack space
 
-global idle_stack_end
+global idle_stack_end: data hidden
 idle_stack_end:

src/kernel/debug.s

@@ -1,32 +1,32 @@
-global get_rsp
+global get_rsp: function hidden
 get_rsp:
 	mov rax, rsp
 	ret
 
-global get_rip
+global get_rip: function hidden
 get_rip:
 	pop rax ; do the same thing as 'ret', except with 'jmp'
 	jmp rax ; with the return address still in rax
 
-global get_caller
+global get_caller: function hidden
 get_caller:
 	; No prelude - don't touch rsp or rbp
 	mov rax, [rbp+8]
 	ret
 
-global get_grandcaller
+global get_grandcaller: function hidden
 get_grandcaller:
 	; No prelude - don't touch rsp or rbp
 	mov rax, [rbp]
 	mov rax, [rax+8]
 	ret
 
-global get_gsbase
+global get_gsbase: function hidden
 get_gsbase:
 	rdgsbase rax
 	ret
 
-global _halt
+global _halt: function hidden
 _halt:
 	hlt
 	jmp _halt

src/kernel/gdtidt.s

@@ -1,15 +1,15 @@
 
-global idt_write
+global idt_write: function hidden
 idt_write:
 	lidt [rdi] ; first arg is the IDT pointer location
 	ret
 
-global idt_load
+global idt_load: function hidden
 idt_load:
 	sidt [rdi] ; first arg is where to write the idtr value
 	ret
 
-global gdt_write
+global gdt_write: function hidden
 gdt_write:
 	lgdt [rdi] ; first arg is the GDT pointer location
 
@@ -28,7 +28,7 @@ gdt_write:
 	ltr cx ; fourth arg is the TSS
 	ret
 
-global gdt_load
+global gdt_load: function hidden
 gdt_load:
 	sgdt [rdi] ; first arg is where to write the gdtr value
 	ret

src/kernel/interrupts.s

@@ -3,7 +3,7 @@
 section .text
 
 extern isr_handler
-global isr_handler_prelude:function (isr_handler_prelude.end - isr_handler_prelude)
+global isr_handler_prelude: function hidden (isr_handler_prelude.end - isr_handler_prelude)
 isr_handler_prelude:
 	push rbp     ; Never executed, fake function prelude
 	mov rbp, rsp ; to calm down gdb
@@ -19,7 +19,7 @@ isr_handler_prelude:
 .end:
 
 extern irq_handler
-global irq_handler_prelude:function (irq_handler_prelude.end - irq_handler_prelude)
+global irq_handler_prelude: function hidden (irq_handler_prelude.end - irq_handler_prelude)
 irq_handler_prelude:
 	push rbp     ; Never executed, fake function prelude
 	mov rbp, rsp ; to calm down gdb
@@ -35,7 +35,7 @@ irq_handler_prelude:
 	; fall through to isr_handler_return
 .end:
 
-global isr_handler_return:function (isr_handler_return.end - isr_handler_return)
+global isr_handler_return: function hidden (isr_handler_return.end - isr_handler_return)
 isr_handler_return:
 	check_swap_gs
 	pop_all
@@ -45,7 +45,7 @@ isr_handler_return:
 .end:
 
 %macro EMIT_ISR 2
-	global %1:function (%1.end - %1)
+	global %1:function hidden (%1.end - %1)
 	%1:
 		push 0
 		push %2
@@ -54,7 +54,7 @@ isr_handler_return:
 %endmacro
 
 %macro EMIT_EISR 2
-	global %1:function (%1.end - %1)
+	global %1:function hidden (%1.end - %1)
 	%1:
 		push %2
 		jmp isr_handler_prelude.real
@@ -62,7 +62,7 @@ isr_handler_return:
 %endmacro
 
 %macro EMIT_IRQ 2
-	global %1:function (%1.end - %1)
+	global %1:function hidden (%1.end - %1)
 	%1:
 		push 0
 		push %2

src/kernel/kernel.ld

@@ -1,53 +1,59 @@
+PHDRS
+{
+    rodata PT_LOAD PHDRS FILEHDR FLAGS (4) /* read-only */;
+    text PT_LOAD ;
+    rwdata PT_LOAD ;
+    bss PT_LOAD ;
+}
+
+MEMORY
+{
+    kernel (rwxa) : ORIGIN = 0xFFFF800000000000, LENGTH = 256M
+}
+
 ENTRY(_kernel_start.real)
+
 SECTIONS
 {
-	. = 0xFFFF800000000000;
+	.header ORIGIN(kernel) + SIZEOF_HEADERS : {
-
+		HIDDEN(__header_start = .);
-	.header : {
-		__header_start = .;
 		KEEP(*(.header))
-		__header_end = .;
+		HIDDEN(__header_end = .);
-	}
+	} :rodata
 
-	.text ALIGN(4096) : {
+    .rodata : {
-		*(.text*)
-		KEEP(*(.isrs))
-	}
-
-	.data ALIGN(4096) : {
-		 *(.data*)
 		 *(.rodata*)
-	}
+    } :rodata
 
-	.ctors : ALIGN(8) {
+    .ap_startup : {
-		 __ctors = .;
+		 *(.ap_startup*)
+    } :rodata
+
+	.ctors ALIGN(8) : {
+		 HIDDEN(__ctors = .);
 		 KEEP(*(.ctors))
 		 KEEP(*(.init_array))
-		 __ctors_end = .;
+		 HIDDEN(__ctors_end = .);
-	 }
+	 } :rodata
 
-	.bss ALIGN(4096) : {
+	.text ALIGN(4K) : {
-		__bss_start = .;
+		*(.text*)
+		KEEP(*(.isrs))
+	} :text
+
+	.data ALIGN(4K) : {
+		 *(.data*)
+	} :rwdata
+
+    .syscall_registry : {
+        *(.syscall_registry*)
+    } :rwdata
+
+	.bss ALIGN(4K) : {
+		HIDDEN(__bss_start = .);
 		*(.bss*)
-		__bss_end = .;
+		HIDDEN(__bss_end = .);
-	}
+	} :bss
 
-	.note : {
+	HIDDEN(__kernel_end = ALIGN(4096));
-		*(.note.*)
-	}
-
-	.eh_frame : {
-		__eh_frame_start = .;
-		KEEP(*(.eh_frame))
-		__eh_frame_end = .;
-	}
-
-	.eh_frame_hdr : {
-		KEEP(*(.eh_frame_hdr))
-	}
-
-	__eh_frame_hdr_start = SIZEOF(.eh_frame_hdr) > 0 ? ADDR(.eh_frame_hdr) : 0;
-	__eh_frame_hdr_end = SIZEOF(.eh_frame_hdr) > 0 ? . : 0;
-
-	kernel_end = ALIGN(4096);
 }

src/kernel/smp.s

@@ -26,7 +26,7 @@ bits 16
 default rel
 align 8
 
-global ap_startup
+global ap_startup: function hidden
 ap_startup:
 	jmp .start_real
 
@@ -104,13 +104,13 @@ align 8
 	jmp rax
 
 
-global ap_startup_code_size
+global ap_startup_code_size: function hidden
 ap_startup_code_size:
 	dq ($ - ap_startup)
 
 
 section .text
-global init_ap_trampoline
+global init_ap_trampoline: function hidden
 init_ap_trampoline:
 	push rbp
 	mov rbp, rsp
@@ -131,7 +131,7 @@ init_ap_trampoline:
 	ret
 
 extern long_ap_startup
-global ap_idle:function (ap_idle.end - ap_idle)
+global ap_idle:function hidden (ap_idle.end - ap_idle)
 ap_idle:
 	call long_ap_startup
 	sti

src/kernel/syscall.s

@@ -22,7 +22,7 @@ extern syscall_registry
 extern syscall_invalid
 
 
-global syscall_handler_prelude:function (syscall_handler_prelude.end - syscall_handler_prelude)
+global syscall_handler_prelude: function hidden (syscall_handler_prelude.end - syscall_handler_prelude)
 syscall_handler_prelude:
 	push rbp     ; Never executed, fake function prelude
 	mov rbp, rsp ; to calm down gdb
@@ -77,7 +77,7 @@ syscall_handler_prelude:
 	call syscall_invalid
 .end:
 
-global kernel_to_user_trampoline:function (kernel_to_user_trampoline.end - kernel_to_user_trampoline)
+global kernel_to_user_trampoline: function hidden (kernel_to_user_trampoline.end - kernel_to_user_trampoline)
 kernel_to_user_trampoline:
 	pop r15
 	pop r14
@@ -98,7 +98,7 @@ kernel_to_user_trampoline:
 	o64 sysret
 .end:
 
-global syscall_enable:function (syscall_enable.end - syscall_enable)
+global syscall_enable: function hidden (syscall_enable.end - syscall_enable)
 syscall_enable:
 	push rbp
 	mov rbp, rsp

src/kernel/task.s

@@ -1,6 +1,6 @@
 %include "tasking.inc"
 
-global task_switch
+global task_switch: function hidden
 task_switch:
 	push rbp
 	mov rbp, rsp
@@ -61,7 +61,7 @@ task_switch:
 	pop rbp
 	ret
 
-global _current_gsbase
+global _current_gsbase: function hidden
 _current_gsbase:
 	mov rax, [gs:CPU_DATA.self]
 	ret

src/libraries/elf/elf/file.h

@@ -22,7 +22,7 @@ public:
     inline size_t size() const { return m_size; }
     inline unsigned count() const { return m_count; }
 
-    inline const T & operator [] (int i) const { return *util::offset_pointer<T>(m_start, m_size*i); }
+    inline const T & operator [] (int i) const { return *util::offset_pointer<const T>(m_start, m_size*i); }
     inline const iterator begin() const { return iterator(m_start, m_size); }
     inline const iterator end() const { return util::offset_pointer(m_start, m_size*m_count); }