infrastructure for dynamic symbol resolution

12 files changed, 149 insertions, 63 deletions

diff --git a/api/elf/elf.h b/api/elf/elf.h
index 3d82bc0..209c219 100644
--- a/api/elf/elf.h
+++ b/api/elf/elf.h
@@ -80,4 +80,5 @@ typedef uint8_t Elf_Byte;
 #define DT_RELAENT 9
 #define DT_STRSZ 10
 #define DT_SYMENT 11
+#define DT_JMPREL 0x17
 
diff --git a/api/elf/elf64.h b/api/elf/elf64.h
index d975c35..9ea3031 100644
--- a/api/elf/elf64.h
+++ b/api/elf/elf64.h
@@ -91,7 +91,8 @@ struct Elf64_Dyn
 #define ELF64_R_TYPE(info) ((Elf64_Word)(info))
 #define ELF64_R_INFO(sym, type) (((Elf64_Xword)(sym)<<32)+(Elf64_Xword)(type))
 
-#define R_AMD64_RELATIVE 8
+#define R_X86_64_JUMP_SLOT 7
+#define R_X86_64_RELATIVE 8
 
 struct Elf64_Rel
 {
diff --git a/kc/api/kc.h b/kc/api/kc.h
index b4a6682..2e3b43c 100644
--- a/kc/api/kc.h
+++ b/kc/api/kc.h
@@ -1,5 +1,13 @@
 #pragma once
 
+#ifndef __ASSEMBLER__
+
+#include <elf/elf64.h>
+
+#include <stddef.h>
+
+#define KC_EXPORT __attribute__((visibility("default")))
+
 extern unsigned char kc_image_base;
 extern unsigned char kc_text_begin;
 extern unsigned char kc_text_end;
@@ -8,5 +16,28 @@ extern unsigned char kc_data_begin;
 extern unsigned char kc_data_end;
 extern unsigned char kc_image_end;
 
-#define KC_EXPORT __attribute__((visibility("default")))
+extern void kc_dynamic_init(void *base, Elf64_Dyn *dyn);
+extern void kc_reloc(
+        void *base,
+        Elf64_Rela *entries,
+        size_t size,
+        size_t entsize);
+
+extern void kc_resolve_symbol(void);
+
+#else
+
+.extern kc_image_base
+.extern kc_text_begin
+.extern kc_text_end
+.extern kc_rodata_begin
+.extern kc_rodata_end
+.extern kc_data_begin
+.extern kc_data_end
+.extern kc_image_end
+.extern _DYNAMIC
+
+.extern kc_dynamic_init
+
+#endif // __ASSEMBLER__
 
diff --git a/kc/boot/Makefile b/kc/boot/Makefile
index 159fec1..44ae161 100644
--- a/kc/boot/Makefile
+++ b/kc/boot/Makefile
@@ -8,7 +8,8 @@ TARGET := efi.os
 .DEFAULT: $(TARGET)
 
 CPPFLAGS += -I../../api -I ../api
-OBJS := entry_x86_64.o reloc_x86_64.o kc_main.o elf64.o memcmp.o memcpy.o \
+OBJS := entry_x86_64.o reloc_x86_64.o dynamic_x86_64.o \
+	kc_main.o elf64.o memcmp.o memcpy.o \
 	memmove.o memset.o loader_paging.o
 
 DEPS := $(patsubst %.o,%.d,$(OBJS))
diff --git a/kc/boot/kc_main.c b/kc/boot/kc_main.c
index 5b32ee6..cb8eb7a 100644
--- a/kc/boot/kc_main.c
+++ b/kc/boot/kc_main.c
@@ -452,6 +452,8 @@ EFI_STATUS kc_main(struct efi_loader_interface *interface)
     e_bs = loader_interface->system_table->BootServices;
     eto = loader_interface->system_table->ConOut;
 
+    plog(L"opening kernel image\r\n");
+
     if (!EFI_ERROR((status = interface->image_open(&kernel_image))) &&
             !EFI_ERROR((status = interface->image_alloc(&kernel_image))) &&
             !EFI_ERROR((status = interface->image_load(&kernel_image))))
diff --git a/kc/core/Makefile b/kc/core/Makefile
index 2c7303e..dede157 100644
--- a/kc/core/Makefile
+++ b/kc/core/Makefile
@@ -10,11 +10,11 @@ CPPFLAGS += -I../../api -I../api -I.
 CFLAGS += -Wno-unused-const-variable -Wno-unused-function -fvisibility=hidden -g
 
 SOBJS := 
-GOBJS := entry_x86_64.o reloc_x86_64.o kprint.o serial.o port.o mmu.o \
-	 kc_main.o memory.o memset.o memcpy.o memmove.o memcmp.o cpu.o \
-	 vm_tree.o exceptions.o panic.o msr.o task.o cpu_task.o irq.o \
-	 kcc_memory.o string.o pic8259.o pic8259_isr.o pit8253.o \
-	 page_early.o page_stack.o strtoull.o
+GOBJS := entry_x86_64.o reloc_x86_64.o dynamic_x86_64.o \
+	 kprint.o serial.o port.o mmu.o kc_main.o memory.o memset.o memcpy.o \
+	 memmove.o memcmp.o cpu.o vm_tree.o exceptions.o panic.o msr.o task.o \
+	 cpu_task.o irq.o kcc_memory.o string.o pic8259.o pic8259_isr.o \
+	 pit8253.o page_early.o page_stack.o strtoull.o
 IOBJS :=
 
 # __attribute__((interrupt)) requires -mgeneral-regs-only
diff --git a/kc/defaults.mk b/kc/defaults.mk
index 588b9b0..0b6c4ba 100644
--- a/kc/defaults.mk
+++ b/kc/defaults.mk
@@ -1,7 +1,7 @@
 
 LIBDIRS += -L$(dir $(shell $(CC) -print-libgcc-file-name))
 LDSCRIPT := ../kc.ld
-LDFLAGS += -z max-page-size=4096 --export-dynamic -pic --no-dynamic-linker \
-	   -z separate-code
+LDFLAGS += -z max-page-size=4096 --export-dynamic -pic \
+	   -z separate-code -pie -Bsymbolic -shared
 LOADLIBES := -lgcc
 
diff --git a/kc/dynamic_x86_64.c b/kc/dynamic_x86_64.c
new file mode 100644
index 0000000..22300d6
--- /dev/null
+++ b/kc/dynamic_x86_64.c
@@ -0,0 +1,53 @@
+#include <kc.h>
+
+void kc_dynamic_init(void *base, Elf64_Dyn *dyn)
+{
+    struct rela
+    {
+        Elf64_Rela *entries;
+        size_t size;
+        size_t entsize;
+    };
+
+    struct rela reladyn = {NULL,};
+    struct rela relaplt = {NULL,};
+
+    Elf64_Addr *gotplt;
+
+    while (dyn && dyn->d_tag != DT_NULL)
+    {
+        switch(dyn->d_tag)
+        {
+            // check for basic relocations first
+            case DT_RELA:
+                reladyn.entries = (Elf64_Rela *)(dyn->d_ptr + (uintptr_t)base);
+                break;
+            case DT_RELASZ:
+                reladyn.size = dyn->d_val;
+                break;
+            // might be combined with JMPRELs so check those too
+            case DT_JMPREL:
+                relaplt.entries = (Elf64_Rela *)(dyn->d_ptr + (uintptr_t)base);
+                break;
+            case DT_PLTRELSZ:
+                relaplt.size = dyn->d_val;
+                break;
+            case DT_RELAENT:
+                reladyn.entsize = dyn->d_val;
+                relaplt.entsize = dyn->d_val;
+                break;
+            case DT_PLTGOT:
+                gotplt = (uintptr_t *)(dyn->d_ptr + (uintptr_t)base);
+                break;
+        }
+        dyn++;
+    }
+
+    // peform relocations
+    //
+    gotplt[1] = (uintptr_t)NULL;
+    gotplt[2] = (uintptr_t)kc_resolve_symbol;
+    kc_reloc(base, relaplt.entries, relaplt.size, relaplt.entsize);
+    kc_reloc(base, reladyn.entries, reladyn.size, reladyn.entsize);
+}
+
diff --git a/kc/entry_x86_64.S b/kc/entry_x86_64.S
index abea8ac..8431044 100644
--- a/kc/entry_x86_64.S
+++ b/kc/entry_x86_64.S
@@ -1,19 +1,30 @@
+#include <kc.h>
+
 .section .text.start
-.extern kc_reloc
-.extern kc_main
-.extern _DYNAMIC
-.extern kc_image_base
 
 .hidden kc_entry
 .global kc_entry
 .type kc_entry, @function
 kc_entry:
     push %rdi
-    lea _DYNAMIC(%rip), %rdi
-    lea kc_image_base(%rip), %rsi
-    call kc_reloc
+    push %rsi
+    lea kc_image_base(%rip), %rdi
+    lea _DYNAMIC(%rip), %rsi
+    call kc_dynamic_init
+    pop %rsi
     pop %rdi
     call kc_main
     ret
 .size kc_entry, . - kc_entry
-    
+
+.section .text
+
+.hidden kc_resolve_symbol
+.global kc_resolve_symbol
+.type kc_resolve_symbol, @function
+kc_resolve_symbol:
+    cli
+    hlt
+    jmp kc_resolve_symbol
+.size kc_resolve_symbol, . - kc_resolve_symbol
+
diff --git a/kc/kc.ld b/kc/kc.ld
index 76e096a..22ee6be 100644
--- a/kc/kc.ld
+++ b/kc/kc.ld
@@ -6,16 +6,14 @@ SECTIONS
 
     . = sizeof_headers;
 
-    .rel :
+    .rela.plt :
     {
-        *(.rel)
-        *(.rel.*)
+        *(.rela.plt)
     }
 
-    .rela :
+    .rela.dyn :
     {
-        *(.rel)
-        *(.rela.*)
+        *(.rela.dyn)
     }
 
     .hash :
@@ -38,18 +36,33 @@ SECTIONS
         PROVIDE_HIDDEN(kc_text_begin = .);
         *(.text.start)
         *(.text)
+    }
+
+    .plt :
+    {
+        *(.plt)
         . = ALIGN(4K);
         PROVIDE_HIDDEN(kc_text_end = .);
     } =0xcc
-
+    
     .dynamic : ALIGN(4K)
     {
+        PROVIDE_HIDDEN(kc_data_begin = .);
         *(.dynamic)
     }
 
+    .got :
+    {
+        *(.got)
+    }
+
+    .got.plt :
+    {
+        *(.got.plt)
+    }
+
     .data :
     {
-        PROVIDE_HIDDEN(kc_data_begin = .);
         *(.rodata)
         *(.data)
     }
diff --git a/kc/reloc_x86_64.c b/kc/reloc_x86_64.c
index c70027f..63dc6e7 100644
--- a/kc/reloc_x86_64.c
+++ b/kc/reloc_x86_64.c
@@ -1,13 +1,9 @@
 #include <kc.h>
 
-#include <elf/elf64.h>
-
-#include <stddef.h>
-
 #define STARTCODE __attribute__((section(".text.start")))
 
 STARTCODE 
-static void do_rela(Elf64_Rela *rela, void *base)
+static void do_rela(void *base, Elf64_Rela *rela)
 {
     union
     {
@@ -20,7 +16,11 @@ static void do_rela(Elf64_Rela *rela, void *base)
 
     switch (ELF64_R_TYPE(rela->r_info))
     {
-        case R_AMD64_RELATIVE:
+        case R_X86_64_JUMP_SLOT:
+            fixup = (void *)(rela->r_offset + (uintptr_t)base);
+            fixup->word64 += (uintptr_t)base;
+            break;
+        case R_X86_64_RELATIVE:
             fixup = (void *)(rela->r_offset + (uintptr_t)base);
             fixup->word64 = (rela->r_addend + (uintptr_t)base);
             break;
@@ -30,40 +30,13 @@ static void do_rela(Elf64_Rela *rela, void *base)
 }
 
 STARTCODE
-void kc_reloc(Elf64_Dyn *dyn, void *base)
+void kc_reloc(void *base, Elf64_Rela *entries, size_t size, size_t entsize)
 {
-    struct
-    {
-        Elf64_Rela *entries;
-        size_t *size;
-        size_t *entsize;
-    }
-    rela = {NULL, NULL, NULL};
-
-    // parse the dynamic segment
-    while (dyn && dyn++->d_tag != DT_NULL)
-    {
-        switch (dyn->d_tag)
-        {
-            case DT_RELA:
-                rela.entries = (Elf64_Rela *)(dyn->d_ptr + (uintptr_t)base);
-                break;
-            case DT_RELASZ:
-                rela.size = &dyn->d_val;
-                break;
-            case DT_RELAENT:
-                rela.entsize = &dyn->d_val;
-                break;
-            default:
-                break;
-        }
-    }
-
     // perform the actual relocation
 
-    for (size_t i = 0; rela.entries && (i < *rela.size / *rela.entsize); i++)
+    for (size_t i = 0; entries && (i < size / entsize); i++)
     {
-        do_rela(&rela.entries[i], base);
+        do_rela(base, &entries[i]);
     }
 }
 
diff --git a/loader/main_efi.c b/loader/main_efi.c
index a6cd7b4..907cedb 100644
--- a/loader/main_efi.c
+++ b/loader/main_efi.c
@@ -134,7 +134,7 @@ EFI_STATUS open_image(struct efi_loader_image *image)
     }
     else
     {
-        Print(L"failed opening image: %r\r\n", status);
+        Print(L"failed opening image %s: %r\r\n", image->path, status);
         return status;
     }