Add symbol table handling and debug backtrace

include/sys/amd64/loader/data.h

@@ -5,6 +5,10 @@
 
 struct amd64_loader_data {
     uint32_t multiboot_info_ptr;
+    uint32_t symtab_ptr;
+    uint32_t symtab_size;
+    uint32_t strtab_ptr;
+    uint32_t strtab_size;
     uint32_t initrd_ptr;
     uint32_t initrd_len;
     char cmdline[KERNEL_CMDLINE_MAX];

include/sys/debug.h

@@ -38,6 +38,10 @@
 #define kfatal(f, ...)      debugf(DEBUG_FATAL,     "\033[41m" DEBUG_BASE_FMT f "\033[0m", DEBUG_BASE_ARGS, ##__VA_ARGS__)
 #define kprint(l, f, ...)   debugf(l,               DEBUG_BASE_FMT f, DEBUG_BASE_ARGS, ##__VA_ARGS__)
 
+void debug_symbol_table_set(uintptr_t symtab, uintptr_t strtab, size_t symtab_size, size_t strtab_size);
+int debug_symbol_find(uintptr_t addr, const char **name, uintptr_t *base);
+void debug_backtrace(uintptr_t rbp, int depth, int limit);
+
 void fmtsiz(char *buf, size_t sz);
 
 void debugc(int level, char c);

sys/amd64/entry.S

@@ -1,6 +1,7 @@
 .section .text
 // Args:
 // %rdi - Address of loader's information struct
+.type _start, %function
 .global _start
 _start:
     cli
@@ -11,12 +12,15 @@ _start:
     call _init
     movq %rbx, %rdi
 
+    xorq %rbp, %rbp
+    pushq %rbp
     call kernel_main
 
 1:
     cli
     hlt
     jmp 1b
+.size _start, . - _start
 
 // Entrypoint for AP bootstrap code
 .global kernel_stacks_top

sys/amd64/hw/exc.c

@@ -2,6 +2,13 @@
 #include "sys/debug.h"
 #include "sys/panic.h"
 
+#define X86_EXCEPTION_PF        14
+
+#define X86_PF_EXEC             (1 << 5)
+#define X86_PF_USER             (1 << 2)
+#define X86_PF_WRITE            (1 << 1)
+#define X86_PF_PRESENT          (1 << 0)
+
 #define X86_FLAGS_CF            (1 << 0)
 #define X86_FLAGS_PF            (1 << 2)
 #define X86_FLAGS_AF            (1 << 4)
@@ -56,5 +63,37 @@ void amd64_exception(struct amd64_exception_frame *frame) {
             (frame->rflags & X86_FLAGS_IF) ? 'I' : '-',
             (frame->rflags & X86_FLAGS_TF) ? 'T' : '-');
 
+    if (frame->exc_no == X86_EXCEPTION_PF) {
+        uintptr_t cr2;
+        asm volatile ("movq %%cr2, %0":"=r"(cr2));
+
+        kfatal("Page fault info:\n");
+        kfatal("Fault address: %p\n", cr2);
+
+        if (frame->exc_code & X86_PF_EXEC) {
+            kfatal(" - Instruction fetch\n");
+        } else {
+            if (frame->exc_code & X86_PF_WRITE) {
+                kfatal(" - Write operation\n");
+            } else {
+                kfatal(" - Read operation\n");
+            }
+        }
+        if (frame->exc_code & X86_PF_PRESENT) {
+            kfatal(" - Refers to non-present page\n");
+        }
+        if (frame->exc_code & X86_PF_USER) {
+            kfatal(" - Userspace\n");
+        }
+    }
+
+    uintptr_t sym_base;
+    const char *sym_name;
+    if (debug_symbol_find(frame->rip, &sym_name, &sym_base) == 0) {
+        kfatal("   Backtrace:\n");
+        kfatal("0: %p <%s + %04x>\n", frame->rip, sym_name, frame->rip - sym_base);
+        debug_backtrace(frame->rbp, 1, 10);
+    }
+
     panic("Exception without resolution\n");
 }

sys/amd64/kernel.c

@@ -35,6 +35,11 @@ void kernel_main(struct amd64_loader_data *data) {
     data = (struct amd64_loader_data *) MM_VIRTUALIZE(data);
     multiboot_info = (multiboot_info_t *) MM_VIRTUALIZE(data->multiboot_info_ptr);
 
+    if (data->symtab_ptr) {
+        kinfo("Kernel symbol table at %p\n", MM_VIRTUALIZE(data->symtab_ptr));
+        debug_symbol_table_set(MM_VIRTUALIZE(data->symtab_ptr), MM_VIRTUALIZE(data->strtab_ptr), data->symtab_size, data->strtab_size);
+    }
+
     // Parse kernel command line
     kernel_set_cmdline(data->cmdline);
 
@@ -56,11 +61,6 @@ void kernel_main(struct amd64_loader_data *data) {
 
     amd64_apic_init();
 
-//#pragma GCC diagnostic ignored "-Wdiv-by-zero"
-//    uint32_t *addr = (uint32_t *) 0x110000000;
-//    *addr = 1;
-//#pragma GCC diagnostic pop
-
     while (1) {
         asm volatile ("sti; hlt");
     }

sys/amd64/loader/loader.c

@@ -45,10 +45,29 @@ static uint64_t elf_load(uintptr_t src) {
     Elf64_Shdr *shdrs = (Elf64_Shdr *) (src + (uintptr_t) ehdr->e_shoff);
     const char *shstrtabd = (const char *) (src + (uintptr_t) shdrs[ehdr->e_shstrndx].sh_offset);
 
+    loader_data.strtab_ptr = 0;
+    loader_data.strtab_size = 0;
+    loader_data.symtab_ptr = 0;
+    loader_data.symtab_size = 0;
+
     for (size_t i = 0; i < (size_t) ehdr->e_shnum; ++i) {
         Elf64_Shdr *shdr = &shdrs[i];
         const char *name = &shstrtabd[shdr->sh_name];
 
+        if (shdr->sh_type == SHT_SYMTAB && !strcmp(name, ".symtab")) {
+            loader_data.symtab_ptr = (uint32_t) shdr->sh_offset + src;
+            loader_data.symtab_size = (uint32_t) shdr->sh_size;
+        }
+
+        if (shdr->sh_type == SHT_STRTAB && !strcmp(name, ".strtab")) {
+            puts("Strtab section: ");
+            puts(name);
+            putc('\n');
+
+            loader_data.strtab_ptr = (uint32_t) shdr->sh_offset + src;
+            loader_data.strtab_size = (uint32_t) shdr->sh_size;
+        }
+
         if (shdr->sh_flags & SHF_ALLOC) {
             if (!strcmp(name, ".note.gnu.property")) {
                 // Fuck you, gcc

sys/debug.c

@@ -4,6 +4,7 @@
 #include "sys/attr.h"
 #include "sys/spin.h"
 #include "sys/config.h"
+#include "sys/elf.h"
 #include <stdint.h>
 
 #if defined(ARCH_AMD64)
@@ -11,6 +12,78 @@
 #include "sys/amd64/hw/rs232.h"
 #endif
 
+////
+
+static uintptr_t g_symtab_ptr = 0;
+static uintptr_t g_strtab_ptr = 0;
+static size_t g_symtab_size = 0;
+static size_t g_strtab_size = 0;
+
+void debug_symbol_table_set(uintptr_t s0, uintptr_t s1, size_t z0, size_t z1) {
+    g_symtab_ptr = s0;
+    g_symtab_size = z0;
+    g_strtab_ptr = s1;
+    g_strtab_size = z1;
+}
+
+int debug_symbol_find(uintptr_t addr, const char **name, uintptr_t *base) {
+    if (g_symtab_ptr && g_strtab_ptr) {
+        size_t offset = 0;
+        Elf64_Sym *sym;
+
+        while (offset < g_symtab_size) {
+            sym = (Elf64_Sym *) (g_symtab_ptr + offset);
+
+            if (ELF_ST_TYPE(sym->st_info) == STT_FUNC) {
+                if (sym->st_value <= addr && sym->st_value + sym->st_size >= addr) {
+                    *base = sym->st_value;
+                    if (sym->st_name < g_strtab_size) {
+                        *name = (const char *) (g_strtab_ptr + sym->st_name);
+                    } else {
+                        *name = "<invalid>";
+                    }
+                    return 0;
+                }
+            }
+
+            offset += sizeof(Elf64_Sym);
+        }
+    }
+
+    return -1;
+}
+
+void debug_backtrace(uintptr_t rbp, int depth, int limit) {
+    // Typical layout:
+    // rbp + 08 == rip
+    // rbp + 00 == rbp_1
+
+    if (!limit) {
+        return;
+    }
+
+    uintptr_t rip =      ((uintptr_t *) rbp)[1];
+    uintptr_t rbp_next = ((uintptr_t *) rbp)[0];
+
+    uintptr_t base;
+    const char *name;
+
+    if (debug_symbol_find(rip, &name, &base) == 0) {
+        kfatal("%d: %p <%s + %04x>\n", depth, rip, name, rip - base);
+    } else {
+        kfatal("%d: %p (unknown)\n", depth, rip);
+    }
+
+    if (rbp_next == 0) {
+        kfatal("-- End of frame chain\n");
+        return;
+    }
+
+    debug_backtrace(rbp_next, depth + 1, limit - 1);
+}
+
+////
+
 static const char *s_debug_xs_set0 = "0123456789abcdef";
 static const char *s_debug_xs_set1 = "0123456789ABCDEF";