#include "tss.h"
/* We load ELF binaries. The following definitions are taken
- from the ELF specification, [ELF], more-or-less verbatim. */
+ from the ELF specification, [ELF1], more-or-less verbatim. */
-/* ELF types. */
+/* ELF types. See [ELF1] 1-2. */
typedef uint32_t Elf32_Word, Elf32_Addr, Elf32_Off;
typedef uint16_t Elf32_Half;
-#define PE32Wx PRIx32
-#define PE32Ax PRIx32
-#define PE32Ox PRIx32
-#define PE32Hx PRIx16
+/* For use with ELF types in printk(). */
+#define PE32Wx PRIx32 /* Print Elf32_Word in hexadecimal. */
+#define PE32Ax PRIx32 /* Print Elf32_Addr in hexadecimal. */
+#define PE32Ox PRIx32 /* Print Elf32_Off in hexadecimal. */
+#define PE32Hx PRIx16 /* Print Elf32_Half in hexadecimal. */
-/* Executable header.
+/* Executable header. See [ELF1] 1-4 to 1-8.
This appears at the very beginning of an ELF binary. */
struct Elf32_Ehdr
{
Elf32_Half e_shstrndx;
};
-/* Program header.
- There are e_phnum of these, starting at file offset e_phoff. */
+/* Program header. See [ELF1] 2-2 to 2-4.
+ There are e_phnum of these, starting at file offset e_phoff
+ (see [ELF1] 1-6). */
struct Elf32_Phdr
{
Elf32_Word p_type;
Elf32_Word p_align;
};
-/* Values for p_type. */
+/* Values for p_type. See [ELF1] 2-3. */
#define PT_NULL 0 /* Ignore. */
#define PT_LOAD 1 /* Loadable segment. */
#define PT_DYNAMIC 2 /* Dynamic linking info. */
#define PT_PHDR 6 /* Program header table. */
#define PT_STACK 0x6474e551 /* Stack segment. */
-/* Flags for p_flags. */
+/* Flags for p_flags. See [ELF3] 2-3 and 2-4. */
#define PF_X 1 /* Executable. */
#define PF_W 2 /* Writable. */
#define PF_R 4 /* Readable. */
-static bool install_page (struct thread *, void *upage, void *kpage);
static bool load_segment (struct thread *, struct file *,
const struct Elf32_Phdr *);
static bool setup_stack (struct thread *);
printk ("addrspace_load: %s: ", filename); \
printk MSG; \
printk ("\n"); \
- goto error; \
+ goto done; \
} while (0)
+/* Loads an ELF executable from FILENAME into T,
+ and stores the executable's entry point into *START.
+ Returns true if successful, false otherwise. */
bool
-addrspace_load (struct thread *t, const char *filename,
- void (**start) (void))
+addrspace_load (struct thread *t, const char *filename, void (**start) (void))
{
struct Elf32_Ehdr ehdr;
struct file file;
break;
case PT_LOAD:
if (!load_segment (t, &file, &phdr))
- goto error;
+ goto done;
break;
}
}
/* Set up stack. */
if (!setup_stack (t))
- goto error;
+ goto done;
/* Start address. */
*start = (void (*) (void)) ehdr.e_entry;
success = true;
- error:
+ done:
+ /* We arrive here whether the load is successful or not.
+ We can distinguish based on `success'. */
if (file_open)
file_close (&file);
if (!success)
return success;
}
+/* Destroys the user address space in T and frees all of its
+ resources. */
void
addrspace_destroy (struct thread *t)
{
}
}
+/* Sets up the CPU for running user code in thread T, if any. */
void
addrspace_activate (struct thread *t)
{
ASSERT (t != NULL);
-
+
+ /* Activate T's page tables. */
pagedir_activate (t->pagedir);
+
+ /* Set T's kernel stack for use in processing interrupts. */
tss_set_esp0 ((uint8_t *) t + PGSIZE);
}
\f
/* addrspace_load() helpers. */
-static bool
-install_page (struct thread *t, void *upage, void *kpage)
-{
- /* Verify that there's not already a page at that virtual
- address, then map our page there. */
- if (pagedir_get_page (t->pagedir, upage) == NULL
- && pagedir_set_page (t->pagedir, upage, kpage, true))
- return true;
- else
- {
- palloc_free (kpage);
- return false;
- }
-}
+static bool install_page (struct thread *, void *upage, void *kpage);
+/* Loads the segment described by PHDR from FILE into thread T's
+ user address space. Return true if successful, false
+ otherwise. */
static bool
load_segment (struct thread *t, struct file *file,
const struct Elf32_Phdr *phdr)
{
- void *start, *end;
- uint8_t *upage;
- off_t filesz_left;
+ void *start, *end; /* Page-rounded segment start and end. */
+ uint8_t *upage; /* Iterator from start to end. */
+ off_t filesz_left; /* Bytes left of file data (as opposed to
+ zero-initialized bytes). */
ASSERT (t != NULL);
ASSERT (file != NULL);
ASSERT (phdr != NULL);
ASSERT (phdr->p_type == PT_LOAD);
- /* p_offset and p_vaddr must be congruent modulo PGSIZE. */
+ /* [ELF1] 2-2 says that p_offset and p_vaddr must be congruent
+ modulo PGSIZE. */
if (phdr->p_offset % PGSIZE != phdr->p_vaddr % PGSIZE)
{
printk ("%#08"PE32Ox" and %#08"PE32Ax" not congruent modulo %#x\n",
return false;
}
- /* p_memsz must be at least as big as p_filesz. */
+ /* [ELF1] 2-3 says that p_memsz must be at least as big as
+ p_filesz. */
if (phdr->p_memsz < phdr->p_filesz)
{
printk ("p_memsz (%08"PE32Wx") < p_filesz (%08"PE32Wx")\n",
return false;
}
- /* Validate virtual memory region to be mapped. */
+ /* Validate virtual memory region to be mapped.
+ The region must both start and end within the user address
+ space range starting at 0 and ending at PHYS_BASE (typically
+ 3 GB == 0xc0000000). */
start = pg_round_down ((void *) phdr->p_vaddr);
end = pg_round_up ((void *) (phdr->p_vaddr + phdr->p_memsz));
if (start >= PHYS_BASE || end >= PHYS_BASE || end < start)
return false;
}
+ /* Load the segment page-by-page into memory. */
filesz_left = phdr->p_filesz + (phdr->p_vaddr & PGMASK);
file_seek (file, ROUND_DOWN (phdr->p_offset, PGSIZE));
for (upage = start; upage < (uint8_t *) end; upage += PGSIZE)
{
+ /* We want to read min(PGSIZE, filesz_left) bytes from the
+ file into the page and zero the rest. */
size_t read_bytes = filesz_left >= PGSIZE ? PGSIZE : filesz_left;
size_t zero_bytes = PGSIZE - read_bytes;
uint8_t *kpage = palloc_get (0);
if (kpage == NULL)
return false;
- if (file_read (file, kpage, read_bytes) != (int) read_bytes)
- return false;
+ /* Do the reading and zeroing. */
+ if (file_read (file, kpage, read_bytes) != (int) read_bytes)
+ {
+ palloc_free (kpage);
+ return false;
+ }
memset (kpage + read_bytes, 0, zero_bytes);
filesz_left -= read_bytes;
- if (!install_page (t, upage, kpage))
- return false;
+ /* Add the page to the process's address space. */
+ if (!install_page (t, upage, kpage))
+ {
+ palloc_free (kpage);
+ return false;
+ }
}
return true;
}
+/* Create a minimal stack for T by mapping a zeroed page at the
+ top of user virtual memory. */
static bool
setup_stack (struct thread *t)
{
- uint8_t *kpage = palloc_get (PAL_ZERO);
- if (kpage == NULL)
+ uint8_t *kpage;
+ bool success = false;
+
+ kpage = palloc_get (PAL_ZERO);
+ if (kpage != NULL)
{
- printk ("failed to allocate process stack\n");
- return false;
+ success = install_page (t, ((uint8_t *) PHYS_BASE) - PGSIZE, kpage);
+ if (!success)
+ palloc_free (kpage);
}
+ else
+ printk ("failed to allocate process stack\n");
- return install_page (t, ((uint8_t *) PHYS_BASE) - PGSIZE, kpage);
+ return success;
}
+/* Adds a mapping from user virtual address UPAGE to kernel
+ virtual address KPAGE to T's page tables. Fails if UPAGE is
+ already mapped or if memory allocation fails. */
+static bool
+install_page (struct thread *t, void *upage, void *kpage)
+{
+ /* Verify that there's not already a page at that virtual
+ address, then map our page there. */
+ return (pagedir_get_page (t->pagedir, upage) == NULL
+ && pagedir_set_page (t->pagedir, upage, kpage, true));
+}
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