From e8c6577617bffa4402c07c7aa20e3c24f03c1c20 Mon Sep 17 00:00:00 2001
From: Benji Dial <benji6283@gmail.com>
Date: Sun, 6 Sep 2020 00:48:07 -0400
Subject: program loading, others

big kernel additions: paging, elf loading, separate kernel and user page allocation
it now properly loads and runs sd0:bin/init.elf
still need to determine which disk was booted from, and start the init on that disk
---
 src/kernel/elf.c | 116 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100644 src/kernel/elf.c

(limited to 'src/kernel/elf.c')

diff --git a/src/kernel/elf.c b/src/kernel/elf.c
new file mode 100644
index 0000000..8cd659c
--- /dev/null
+++ b/src/kernel/elf.c
@@ -0,0 +1,116 @@
+#include <stdint.h>
+#include "drive.h"
+#include "elf.h"
+#include "task.h"
+#include "util.h"
+#include "paging.h"
+#include "pmap.h"
+
+#define ELF_MAGIC 0x464c457f
+
+enum {
+  ELF_32 = 1,
+  ELF_64 = 2
+};
+
+enum {
+  LITTLE_ENDIAN = 1,
+  BIG_ENDIAN    = 2
+};
+
+enum {
+  //...
+  ARCH_X86 = 0x03
+  //...
+};
+
+struct elf_header {
+  uint32_t magic;
+  uint8_t word_size;
+  uint8_t endianness;
+  uint8_t elf_version;
+  uint8_t target_os;//ignored
+  uint8_t os_abi_version;//should be zero
+  uint8_t reserved[7];
+  uint16_t object_type;//TODO
+  uint16_t architecture;//should be ARCH_X86
+  uint32_t elf_version_2;
+  uint32_t entry_vma;
+  uint32_t phtable_fa;
+  uint32_t shtable_fa;
+  uint32_t flags;
+  uint16_t eh_size;
+  uint16_t phentry_size;
+  uint16_t phtable_count;
+  uint16_t shentry_size;
+  uint16_t shtable_count;
+  uint16_t sh_names_entry;
+} __attribute__ ((packed));
+
+enum {
+  PT_UNUSED  = 0,
+  PT_LOADME  = 1,
+  PT_DYNLINK = 2,
+  PT_INTERP  = 3,
+  PT_COMMENT = 4,
+  PT_SHARED  = 5,
+  PT_PHTABLE = 6,
+  PT_TL_TMPL = 7
+};
+
+enum {
+  PH_WRITABLE = 0x02
+};
+
+struct ph_entry {
+  uint32_t type;
+  uint32_t fa;
+  uint32_t vma;//must be page-aligned
+  uint32_t pma;//ignored
+  uint32_t fs;
+  uint32_t vms;
+  uint32_t flags;
+  uint32_t align;
+} __attribute__ ((packed));
+
+bool try_elf_run(const struct drive *d, const char *path) {
+  file_id_t h = d->get_file(d, path);
+  if (!h)
+    return false;
+
+  struct elf_header ehead;
+
+  fmcpy(&ehead, d, h, 0, sizeof(struct elf_header));
+
+  if ((ehead.magic != ELF_MAGIC) ||
+      (ehead.word_size != ELF_32) ||
+      (ehead.endianness != LITTLE_ENDIAN) ||
+       ehead.os_abi_version) {
+    d->free_file(d, h);
+    return false;
+  }
+
+  uint32_t phtable_size = ehead.phentry_size * ehead.phtable_count;
+  uint16_t phtable_pages = (phtable_size - 1) / 4096 + 1;
+
+  void *phtable = allocate_kernel_pages(phtable_pages);
+  fmcpy(phtable, d, h, ehead.phtable_fa, phtable_size);
+
+  void *pd = new_task_pd();
+
+  for (uint32_t phi = 0; phi < ehead.phtable_count; ++phi) {
+    struct ph_entry *entry = phtable + phi * ehead.phentry_size;
+    if (entry->type != PT_LOADME)
+      continue;
+    void *pma = pd_user_allocate(pd, entry->vma, (entry->vms - 1) / 4096 + 1, entry->flags & PH_WRITABLE);
+    fmcpy(pma, d, h, entry->fa, entry->fs);
+  }
+
+  free_pages(phtable, phtable_pages);
+
+  struct task_state tstate;
+  tstate.page_directory = pd;
+  tstate.ret_addr = ehead.entry_vma;
+  new_task(tstate);
+  return true;
+}
\ No newline at end of file
-- 
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