[PATCH] generic ELF loading

[Hollis Blanchard]

This patch adds generic ELF loading infrastructure for both 32-bit and
64-bit ELF. It provides an "iterate" function for program headers, and a
"load" function for convenience.

I have converted the PowerPC Linux loader to use this infrastructure
(see next mail), and possibly the i386 multiboot loader as well (though
I will need others to test it). The module loader looks a little more
annoying because it actually loads *sections*, not segments.

I will be away next week but intend to commit this soon after, so please
review.

This code is literally duplicated, once for 32-bit and once for 64-bit.
I'm trying to come up with a better way of doing that, and I'm
considering something like this:

        elf32.c:
        #define Elf_Ehdr Elf32_Ehdr
        #define Elf_Phdr Elf32_Phdr
        #include "elfclass.c"
        
        elf64.c:
        #define Elf_Ehdr Elf64_Ehdr
        #define Elf_Phdr Elf64_Phdr
        #include "elfclass.c"

If you strongly object to #including C files, or have a better way of
doing this, please speak up.

-Hollis

diff -r b53dfa2812ad include/grub/elfload.h
--- /dev/null   Thu Jan 01 00:00:00 1970 +0000
+++ b/include/grub/elfload.h    Fri Oct 13 16:23:22 2006 -0500
@@ -0,0 +1,57 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2003, 2004, 2005, 2006  Free Software Foundation, Inc.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#ifndef GRUB_ELFLOAD_HEADER
+#define GRUB_ELFLOAD_HEADER    1
+
+#include <grub/err.h>
+#include <grub/elf.h>
+#include <grub/file.h>
+#include <grub/symbol.h>
+#include <grub/types.h>
+
+struct grub_elf_file
+{
+  grub_file_t file;
+  union {
+    Elf64_Ehdr ehdr64;
+    Elf32_Ehdr ehdr32;
+  } ehdr;
+  void *phdrs;
+};
+typedef struct grub_elf_file *grub_elf_t;
+
+grub_elf_t EXPORT_FUNC(grub_elf_open) (const char *name);
+grub_err_t EXPORT_FUNC(grub_elf_close) (grub_elf_t elf);
+
+int EXPORT_FUNC(grub_elf_is_elf32) (grub_elf_t elf);
+grub_err_t EXPORT_FUNC(grub_elf32_phdr_iterate) (grub_elf_t elf,
+                        int (*hook) (grub_elf_t, Elf32_Phdr *, void *),
+                        void *hook_arg);
+grub_err_t EXPORT_FUNC(grub_elf32_load) (grub_elf_t elf,
+                                        int (*) (Elf32_Phdr *));
+
+int EXPORT_FUNC(grub_elf_is_elf64) (grub_elf_t elf);
+grub_err_t EXPORT_FUNC(grub_elf64_phdr_iterate) (grub_elf_t elf,
+                        int (*hook) (grub_elf_t, Elf64_Phdr *, void *),
+                        void *hook_arg);
+grub_err_t EXPORT_FUNC(grub_elf64_load) (grub_elf_t elf,
+                                        int (*) (Elf64_Phdr *));
+
+#endif /* ! GRUB_ELFLOAD_HEADER */
diff -r b53dfa2812ad kern/elf.c
--- /dev/null   Thu Jan 01 00:00:00 1970 +0000
+++ b/kern/elf.c        Fri Oct 13 16:23:22 2006 -0500
@@ -0,0 +1,280 @@
+/* elf.c - load ELF files */
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2003, 2004, 2005, 2006  Free Software Foundation, Inc.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <grub/err.h>
+#include <grub/elf.h>
+#include <grub/elfload.h>
+#include <grub/file.h>
+#include <grub/misc.h>
+#include <grub/mm.h>
+
+/* Check if EHDR is a valid ELF header.  */
+static grub_err_t
+grub_elf_check_header (grub_elf_t elf)
+{
+  Elf32_Ehdr *e = &elf->ehdr.ehdr32;
+
+  if (e->e_ident[EI_MAG0] != ELFMAG0
+      || e->e_ident[EI_MAG1] != ELFMAG1
+      || e->e_ident[EI_MAG2] != ELFMAG2
+      || e->e_ident[EI_MAG3] != ELFMAG3
+      || e->e_ident[EI_VERSION] != EV_CURRENT
+      || e->e_version != EV_CURRENT)
+    return grub_error (GRUB_ERR_BAD_OS, "invalid arch independent ELF magic");
+
+  return GRUB_ERR_NONE;
+}
+
+grub_err_t
+grub_elf_close (grub_elf_t elf)
+{
+  grub_file_t file = elf->file;
+
+  grub_free (elf->phdrs);
+  grub_free (elf);
+
+  if (file)
+    grub_file_close (file);
+
+  return grub_errno;
+}
+
+grub_elf_t
+grub_elf_open (const char *name)
+{
+  grub_elf_t elf;
+
+  elf = grub_malloc (sizeof (*elf));
+  if (! elf)
+    return 0;
+
+  elf->file = 0;
+  elf->phdrs = 0;
+
+  elf->file = grub_file_open (name);
+  if (! elf->file)
+    goto fail;
+
+  if (grub_file_read (elf->file, (char *) &elf->ehdr, sizeof (elf->ehdr))
+      != sizeof (elf->ehdr))
+    {
+      grub_error (GRUB_ERR_READ_ERROR, "Cannot read ELF header.");
+      goto fail;
+    }
+
+  if (grub_elf_check_header (elf))
+    goto fail;
+
+  return elf;
+
+fail:
+  grub_elf_close (elf);
+  return 0;
+}
+
+
+/* 32-bit */
+
+int
+grub_elf_is_elf32 (grub_elf_t elf)
+{
+  return elf->ehdr.ehdr32.e_ident[EI_CLASS] == ELFCLASS32;
+}
+
+typedef int (*grub_elf32_load_hook_t) (Elf32_Phdr *phdr);
+
+static int
+grub_elf32_load_segment (grub_elf_t elf, Elf32_Phdr *phdr,
+                        void *hook)
+{
+  grub_elf32_load_hook_t load_hook = (grub_elf32_load_hook_t) hook;
+
+  if (phdr->p_type != PT_LOAD)
+    return 0;
+
+  if (load_hook && load_hook (phdr))
+    return 1;
+
+  grub_dprintf ("loader", "Loading segment at %llx, size 0x%llx\n",
+               (unsigned long long) phdr->p_paddr,
+               (unsigned long long) phdr->p_filesz);
+
+  if (grub_file_seek (elf->file, phdr->p_offset) == (grub_off_t) -1)
+    {
+      return grub_error (GRUB_ERR_BAD_OS, "Invalid offset in program header");
+    }
+
+  if (grub_file_read (elf->file, (void *) (long) phdr->p_paddr, phdr->p_filesz)
+      != (grub_ssize_t) phdr->p_filesz)
+    {
+      return grub_error (GRUB_ERR_BAD_OS, "Couldn't load segment");
+    }
+
+  if (phdr->p_filesz < phdr->p_memsz)
+    grub_memset ((void *) (unsigned long) (phdr->p_paddr + phdr->p_filesz),
+                0, phdr->p_memsz - phdr->p_filesz);
+
+  return 0;
+}
+
+static grub_err_t
+grub_elf32_load_phdrs (grub_elf_t elf)
+{
+  grub_ssize_t phdrs_size;
+
+  phdrs_size = elf->ehdr.ehdr32.e_phnum * elf->ehdr.ehdr32.e_phentsize;
+
+  grub_dprintf ("elf", "loading program headers: offset 0x%llx, size 0x%x\n",
+               (unsigned long long) elf->ehdr.ehdr32.e_phoff,
+               phdrs_size);
+
+  elf->phdrs = grub_malloc (phdrs_size);
+  if (! elf->phdrs)
+    return grub_errno;
+
+  if ((grub_file_seek (elf->file, elf->ehdr.ehdr32.e_phoff) == (grub_off_t) -1)
+      || (grub_file_read (elf->file, elf->phdrs, phdrs_size) != phdrs_size))
+    return grub_error (GRUB_ERR_READ_ERROR, "Cannot read program headers");
+
+  return GRUB_ERR_NONE;
+}
+
+grub_err_t
+grub_elf32_phdr_iterate (grub_elf_t elf,
+                        int (*hook) (grub_elf_t, Elf32_Phdr *, void *),
+                        void *hook_arg)
+{
+  Elf32_Phdr *phdrs;
+  unsigned int i;
+
+  if (! elf->phdrs)
+    if (grub_elf32_load_phdrs (elf))
+      return grub_errno;
+
+  phdrs = (Elf32_Phdr *) elf->phdrs;
+  for (i = 0; i < elf->ehdr.ehdr32.e_phnum; i++)
+    if (hook (elf, phdrs + i, hook_arg))
+      break;
+
+  return grub_errno;
+}
+
+/* Load every loadable segment into memory.  */
+grub_err_t
+grub_elf32_load (grub_elf_t elf, int (*phdr_hook) (Elf32_Phdr *))
+{
+  return grub_elf32_phdr_iterate (elf, grub_elf32_load_segment,
+                                 phdr_hook);
+}
+
+
+/* 64-bit */
+
+int
+grub_elf_is_elf64 (grub_elf_t elf)
+{
+  return elf->ehdr.ehdr64.e_ident[EI_CLASS] == ELFCLASS64;
+}
+
+typedef int (*grub_elf64_load_hook_t) (Elf64_Phdr *phdr);
+
+static int
+grub_elf64_load_segment (grub_elf_t elf, Elf64_Phdr *phdr,
+                        void *hook)
+{
+  grub_elf64_load_hook_t load_hook = (grub_elf64_load_hook_t) hook;
+
+  if (phdr->p_type != PT_LOAD)
+    return 0;
+
+  if (load_hook && load_hook (phdr))
+    return 1;
+
+  grub_dprintf ("loader", "Loading segment at %llx, size 0x%llx\n",
+               (unsigned long long) phdr->p_paddr,
+               (unsigned long long) phdr->p_filesz);
+
+  if (grub_file_seek (elf->file, phdr->p_offset) == (grub_off_t) -1)
+    {
+      return grub_error (GRUB_ERR_BAD_OS, "Invalid offset in program header");
+    }
+
+  if (grub_file_read (elf->file, (void *) (long) phdr->p_paddr, phdr->p_filesz)
+      != (grub_ssize_t) phdr->p_filesz)
+    {
+      return grub_error (GRUB_ERR_BAD_OS, "Couldn't load segment");
+    }
+
+  if (phdr->p_filesz < phdr->p_memsz)
+    grub_memset ((void *) (unsigned long) (phdr->p_paddr + phdr->p_filesz),
+                0, phdr->p_memsz - phdr->p_filesz);
+
+  return 0;
+}
+
+static grub_err_t
+grub_elf64_load_phdrs (grub_elf_t elf)
+{
+  grub_ssize_t phdrs_size;
+
+  phdrs_size = elf->ehdr.ehdr64.e_phnum * elf->ehdr.ehdr64.e_phentsize;
+
+  grub_dprintf ("elf", "loading program headers: offset 0x%llx, size 0x%x\n",
+               (unsigned long long) elf->ehdr.ehdr64.e_phoff,
+               phdrs_size);
+
+  elf->phdrs = grub_malloc (phdrs_size);
+  if (! elf->phdrs)
+    return grub_errno;
+
+  if ((grub_file_seek (elf->file, elf->ehdr.ehdr64.e_phoff) == (grub_off_t) -1)
+      || (grub_file_read (elf->file, elf->phdrs, phdrs_size) != phdrs_size))
+    return grub_error (GRUB_ERR_READ_ERROR, "Cannot read program headers");
+
+  return GRUB_ERR_NONE;
+}
+
+grub_err_t
+grub_elf64_phdr_iterate (grub_elf_t elf,
+                        int (*hook) (grub_elf_t, Elf64_Phdr *, void *),
+                        void *hook_arg)
+{
+  Elf64_Phdr *phdrs;
+  unsigned int i;
+
+  if (! elf->phdrs)
+    if (grub_elf64_load_phdrs (elf))
+      return grub_errno;
+
+  phdrs = (Elf64_Phdr *) elf->phdrs;
+  for (i = 0; i < elf->ehdr.ehdr64.e_phnum; i++)
+    if (hook (elf, phdrs + i, hook_arg))
+      break;
+
+  return grub_errno;
+}
+
+/* Load every loadable segment into memory.  */
+grub_err_t
+grub_elf64_load (grub_elf_t elf, int (*phdr_hook) (Elf64_Phdr *))
+{
+  return grub_elf64_phdr_iterate (elf, grub_elf64_load_segment,
+                                 phdr_hook);
+}