Hi,
It seems when adding the relocators for ELF, I failed to notice both ELF and
a.out loaders share the same grub_multiboot_real_boot function, and hence my
code was trashing %eax.
Since this functionality is useful for the a.out loader anyway, I decided to
implement it as well. In the process I did some cleanup, mostly to reduce
code duplication among both users of the relocators.
So here's the patch. Please comment!
--
Robert Millan
The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
how) you may access your data; but nobody's threatening your freedom: we
still allow you to remove your data and not access it at all."
Index: kern/i386/loader.S
===================================================================
--- kern/i386/loader.S (revision 1787)
+++ kern/i386/loader.S (working copy)
@@ -132,6 +132,36 @@
VARIABLE(grub_multiboot_payload_entry_offset)
.long 0
+/*
+ * The relocators below understand the following parameters:
+ * ecx: Size of the block to be copied.
+ * esi: Where to copy from (always lowest address, even if we're relocating
+ * backwards).
+ * edi: Where to copy to (likewise).
+ * edx: Offset of the entry point (relative to the beginning of the block).
+ */
+VARIABLE(grub_multiboot_forward_relocator)
+ cld
+ addl %edi, %edx
+ rep
+ movsb
+ jmp *%edx
+VARIABLE(grub_multiboot_forward_relocator_end)
+
+VARIABLE(grub_multiboot_backward_relocator)
+ std
+ addl %ecx, %esi
+ addl %ecx, %edi
+ /* backward movsb is implicitly off-by-one. compensate that. */
+ incl %ecx
+ rep
+ movsb
+ /* same problem again. */
+ incl %edi
+ addl %edi, %edx
+ jmp *%edx
+VARIABLE(grub_multiboot_backward_relocator_end)
+
FUNCTION(grub_multiboot_real_boot)
/* Push the entry address on the stack. */
pushl %eax
@@ -149,11 +179,14 @@
movl EXT_C(grub_multiboot_payload_size), %ecx
movl EXT_C(grub_multiboot_payload_orig), %esi
movl EXT_C(grub_multiboot_payload_dest), %edi
- movl EXT_C(grub_multiboot_payload_entry_offset), %eax
-
+ movl EXT_C(grub_multiboot_payload_entry_offset), %edx
+
+ /* Move the magic value into eax. */
+ movl $MULTIBOOT_MAGIC2, %eax
+
/* Jump to the relocator. */
- popl %edx
- jmp *%edx
+ popl %ebp
+ jmp *%ebp
/*
* This starts the multiboot 2 kernel.
Index: include/grub/i386/loader.h
===================================================================
--- include/grub/i386/loader.h (revision 1787)
+++ include/grub/i386/loader.h (working copy)
@@ -53,4 +53,11 @@
void grub_rescue_cmd_linux (int argc, char *argv[]);
void grub_rescue_cmd_initrd (int argc, char *argv[]);
+extern grub_uint8_t EXPORT_VAR(grub_multiboot_forward_relocator);
+extern grub_uint8_t EXPORT_VAR(grub_multiboot_forward_relocator_end);
+extern grub_uint8_t EXPORT_VAR(grub_multiboot_backward_relocator);
+extern grub_uint8_t EXPORT_VAR(grub_multiboot_backward_relocator_end);
+
+#define RELOCATOR_SIZEOF(x) (&grub_multiboot_##x##_relocator_end - &grub_multiboot_##x##_relocator)
+
#endif /* ! GRUB_LOADER_CPU_HEADER */
Index: loader/i386/pc/multiboot.c
===================================================================
--- loader/i386/pc/multiboot.c (revision 1787)
+++ loader/i386/pc/multiboot.c (working copy)
@@ -52,31 +52,6 @@
static char *playground = NULL;
-static grub_uint8_t forward_relocator[] =
-{
- 0xfc, /* cld */
- 0x89, 0xf2, /* movl %esi, %edx */
- 0xf3, 0xa4, /* rep movsb */
- 0x01, 0xc2, /* addl %eax, %edx */
- 0xb8, 0x02, 0xb0, 0xad, 0x2b, /* movl $MULTIBOOT_MAGIC2, %eax */
- 0xff, 0xe2, /* jmp *%edx */
-};
-
-static grub_uint8_t backward_relocator[] =
-{
- 0xfd, /* std */
- 0x01, 0xce, /* addl %ecx, %esi */
- 0x01, 0xcf, /* addl %ecx, %edi */
- /* backward movsb is implicitly off-by-one. compensate that. */
- 0x41, /* incl %ecx */
- 0xf3, 0xa4, /* rep movsb */
- /* same problem again. */
- 0x47, /* incl %edi */
- 0x01, 0xc7, /* addl %eax, %edi */
- 0xb8, 0x02, 0xb0, 0xad, 0x2b, /* movl $MULTIBOOT_MAGIC2, %eax */
- 0xff, 0xe7, /* jmp *%edi */
-};
-
static grub_err_t
grub_multiboot_boot (void)
{
@@ -155,17 +130,12 @@
grub_multiboot_payload_size = (phdr(highest_segment)->p_paddr + phdr(highest_segment)->p_memsz) - phdr(lowest_segment)->p_paddr;
grub_multiboot_payload_dest = phdr(lowest_segment)->p_paddr;
- if (playground)
- grub_free (playground);
- playground = grub_malloc (sizeof (forward_relocator) + grub_multiboot_payload_size + sizeof (backward_relocator));
+ playground = grub_malloc (RELOCATOR_SIZEOF(forward) + grub_multiboot_payload_size + RELOCATOR_SIZEOF(backward));
if (! playground)
return grub_errno;
- grub_multiboot_payload_orig = (long) playground + sizeof (forward_relocator);
+ grub_multiboot_payload_orig = (long) playground + RELOCATOR_SIZEOF(forward);
- grub_memmove (playground, forward_relocator, sizeof (forward_relocator));
- grub_memmove ((char *) (grub_multiboot_payload_orig + grub_multiboot_payload_size), backward_relocator, sizeof (backward_relocator));
-
/* Load every loadable segment in memory. */
for (i = 0; i < ehdr->e_phnum; i++)
{
@@ -196,16 +166,6 @@
#undef phdr
- if (grub_multiboot_payload_dest >= grub_multiboot_payload_orig)
- entry = (grub_addr_t) playground;
- else
- entry = (grub_addr_t) grub_multiboot_payload_orig + grub_multiboot_payload_size;
-
- grub_dprintf ("multiboot_loader", "dest=%p, size=0x%x, entry_offset=0x%x\n",
- (void *) grub_multiboot_payload_dest,
- grub_multiboot_payload_size,
- grub_multiboot_payload_entry_offset);
-
return grub_errno;
}
@@ -413,24 +373,66 @@
goto fail;
}
+ if (playground)
+ {
+ grub_free (playground);
+ playground = NULL;
+ }
+
if (header->flags & MULTIBOOT_AOUT_KLUDGE)
{
- int ofs;
+ int offset = ((char *) header - buffer -
+ (header->header_addr - header->load_addr));
+ int load_size = ((header->load_end_addr == 0) ? file->size - offset :
+ header->load_end_addr - header->load_addr);
- ofs = (char *) header - buffer -
- (header->header_addr - header->load_addr);
- if ((grub_aout_load (file, ofs, header->load_addr,
- ((header->load_end_addr == 0) ? 0 :
- header->load_end_addr - header->load_addr),
- header->bss_end_addr))
- !=GRUB_ERR_NONE)
- goto fail;
+ if (header->bss_end_addr)
+ grub_multiboot_payload_size = (header->bss_end_addr - header->load_addr);
+ else
+ grub_multiboot_payload_size = load_size;
+ grub_multiboot_payload_dest = header->load_addr;
- entry = header->entry_addr;
+ playground = grub_malloc (RELOCATOR_SIZEOF(forward) + grub_multiboot_payload_size + RELOCATOR_SIZEOF(backward));
+ if (! playground)
+ goto fail;
+
+ grub_multiboot_payload_orig = (long) playground + RELOCATOR_SIZEOF(forward);
+
+ if ((grub_file_seek (file, offset)) == (grub_off_t) - 1)
+ goto fail;
+
+ grub_file_read (file, grub_multiboot_payload_orig, load_size);
+ if (grub_errno)
+ goto fail;
+
+ if (header->bss_end_addr)
+ grub_memset (grub_multiboot_payload_orig + load_size, 0,
+ header->bss_end_addr - header->load_addr - load_size);
+
+ grub_multiboot_payload_entry_offset = header->entry_addr - header->load_addr;
+
}
else if (grub_multiboot_load_elf (file, buffer) != GRUB_ERR_NONE)
goto fail;
+
+ if (grub_multiboot_payload_dest >= grub_multiboot_payload_orig)
+ {
+ grub_memmove (playground, &grub_multiboot_forward_relocator, RELOCATOR_SIZEOF(forward));
+ entry = (grub_addr_t) playground;
+ }
+ else
+ {
+ grub_memmove ((char *) (grub_multiboot_payload_orig + grub_multiboot_payload_size),
+ &grub_multiboot_backward_relocator, RELOCATOR_SIZEOF(backward));
+ entry = (grub_addr_t) grub_multiboot_payload_orig + grub_multiboot_payload_size;
+ }
+
+ grub_dprintf ("multiboot_loader", "dest=%p, size=0x%x, entry_offset=0x%x\n",
+ (void *) grub_multiboot_payload_dest,
+ grub_multiboot_payload_size,
+ grub_multiboot_payload_entry_offset);
+
mbi = grub_malloc (sizeof (struct grub_multiboot_info));
if (! mbi)
goto fail;
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