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Re: [Xen-devel] [GRUB2 PATCH v3 4/4] multiboot2: Add support for relocatable images
- To: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
- From: "Vladimir 'phcoder' Serbinenko" <phcoder@xxxxxxxxx>
- Date: Thu, 10 Mar 2016 21:41:26 +0100
- Cc: "jgross@xxxxxxxx" <jgross@xxxxxxxx>, "grub-devel@xxxxxxx" <grub-devel@xxxxxxx>, "eric.snowberg@xxxxxxxxxx" <eric.snowberg@xxxxxxxxxx>, "arvidjaar@xxxxxxxxx" <arvidjaar@xxxxxxxxx>, "andrew.cooper3@xxxxxxxxxx" <andrew.cooper3@xxxxxxxxxx>, "cardoe@xxxxxxxxxx" <cardoe@xxxxxxxxxx>, "pgnet.dev@xxxxxxxxx" <pgnet.dev@xxxxxxxxx>, "roy.franz@xxxxxxxxxx" <roy.franz@xxxxxxxxxx>, "ning.sun@xxxxxxxxx" <ning.sun@xxxxxxxxx>, "david.vrabel@xxxxxxxxxx" <david.vrabel@xxxxxxxxxx>, "jbeulich@xxxxxxxx" <jbeulich@xxxxxxxx>, "stefano.stabellini@xxxxxxxxxxxxx" <stefano.stabellini@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "qiaowei.ren@xxxxxxxxx" <qiaowei.ren@xxxxxxxxx>, "richard.l.maliszewski@xxxxxxxxx" <richard.l.maliszewski@xxxxxxxxx>, "gang.wei@xxxxxxxxx" <gang.wei@xxxxxxxxx>, "fu.wei@xxxxxxxxxx" <fu.wei@xxxxxxxxxx>, "seth.goldberg@xxxxxxxxxx" <seth.goldberg@xxxxxxxxxx>
- Delivery-date: Thu, 10 Mar 2016 20:41:44 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On Wednesday, March 2, 2016, Daniel Kiper <daniel.kiper@xxxxxxxxxx> wrote:
Currently multiboot2 protocol loads image exactly at address specified in
ELF or multiboot2 header. This solution works quite well on legacy BIOS
platforms. It is possible because memory regions are placed at predictable
addresses (though I was not able to find any spec which says that it is
strong requirement, so, it looks that it is just a goodwill of hardware
designers). However, EFI platforms are more volatile. Even if required
memory regions live at specific addresses then they are sometimes simply
not free (e.g. used by boot/runtime services on Dell PowerEdge R820 and
OVMF). This means that you are not able to simply set up final image
destination on build time. You have to provide method to relocate image
contents to real load address which is usually different than load address
specified in ELF and multiboot2 headers.
This patch provides all needed machinery to do self relocation in image code.
First of all GRUB2 reads min_addr (min. load addr), max_addr (max. load addr),
align (required image alignment), preference (it says which memory regions are
preferred by image, e.g. none, low, high) from multiboot_header_tag_relocatable
header tag contained in binary. Later loader tries to fulfill request (not only
that one) and if it succeeds then it informs image about real load address via
multiboot_tag_base_addr tag. At this stage GRUB2 role is finished. Starting
from now executable must cope with relocations itself using whole static
and dynamic knowledge provided by boot loader.
This patch does not provide functionality which could do relocations using
ELF relocation data. However, I was asked by Konrad Rzeszutek Wilk and Vladimir
'phcoder' Serbinenko to investigate that thing. It looks that relevant machinery
could be added to existing code (including this patch) without huge effort.
Additionally, ELF relocation could live in parallel with self relocation provided
by this patch. However, during research I realized that first of all we should
establish the details how ELF relocatable image should look like and how it should
be build. At least to build proper test/example files.
As I saw multiboot2 protocol is able to consume ET_EXEC and ET_DYN ELF files.
Potentially we can use ET_DYN file type. It can be build with gcc/ld -pie option.
However, it contains a lot of unneeded stuff (e.g. INTERP, DYNAMIC, GNU_EH_FRAME
program headers) and it could be quite difficult to drop them (Hmmm... Is it
possible to build it properly with custom ld script?). How big are they? Are they a real problem? So, I have checked ET_EXEC
file type. Sadly in this case linker by default resolves all local symbol relocations
and removes relocation related sections. Fortunately it is possible to leave them
as is with simple -q/--emit-relocs ld option. However, output file is quite fragile
and any operation on it should be done with great care (e.g. strip should be called
with --strip-unneeded option). So, this solution is not perfect too. It means that
maybe we should look for better solution. However, I think that we should not use
any custom tools and focus on functionalities provided by compiler and binutils.
In this context ld scripts looks quite promising but maybe you have better solutions.
So, what do you think about that?
Another possibility is to use intermediary .o files like we do for modules and like Linux does for modules AFAIR.
This patch was tested with Xen image which uses that functionality. However, this Xen
feature is still under development and new patchset will be released in about 3-4 weeks.
Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
---
v3 - suggestions/fixes:
- reduce number of casts
(suggested by Konrad Rzeszutek Wilk),
- remove unneeded space at the end of line
(suggested by Konrad Rzeszutek Wilk),
- improve commit message
(suggested by Konrad Rzeszutek Wilk).
---
grub-core/loader/i386/multiboot_mbi.c | 6 ++-
grub-core/loader/multiboot.c | 12 ++++--
grub-core/loader/multiboot_elfxx.c | 28 ++++++++++----
grub-core/loader/multiboot_mbi2.c | 65 ++++++++++++++++++++++++++++++---
include/grub/multiboot.h | 4 +-
include/multiboot2.h | 24 ++++++++++++
6 files changed, 120 insertions(+), 19 deletions(-)
diff --git a/grub-core/loader/i386/multiboot_mbi.c b/grub-core/loader/i386/multiboot_mbi.c
index f60b702..4fc83ed 100644
--- a/grub-core/loader/i386/multiboot_mbi.c
+++ b/grub-core/loader/i386/multiboot_mbi.c
@@ -72,7 +72,8 @@ load_kernel (grub_file_t file, const char *filename,
grub_err_t err;
if (grub_multiboot_quirks & GRUB_MULTIBOOT_QUIRK_BAD_KLUDGE)
{
- err = grub_multiboot_load_elf (file, filename, buffer);
+ err = grub_multiboot_load_elf (file, filename, buffer, 0, 0, 0, 0,
+ GRUB_RELOCATOR_PREFERENCE_NONE, NULL, 0);
if (err == GRUB_ERR_NONE) {
return GRUB_ERR_NONE;
}
@@ -121,7 +122,8 @@ load_kernel (grub_file_t file, const char *filename,
return GRUB_ERR_NONE;
}
- return grub_multiboot_load_elf (file, filename, buffer);
+ return grub_multiboot_load_elf (file, filename, buffer, 0, 0, 0, 0,
+ GRUB_RELOCATOR_PREFERENCE_NONE, NULL, 0);
}
static struct multiboot_header *
diff --git a/grub-core/loader/multiboot.c b/grub-core/loader/multiboot.c
index 18038fd..c0f51b6 100644
--- a/grub-core/loader/multiboot.c
+++ b/grub-core/loader/multiboot.c
@@ -208,12 +208,18 @@ static grub_uint64_t highest_load;
/* Load ELF32 or ELF64. */
grub_err_t
grub_multiboot_load_elf (grub_file_t file, const char *filename,
- void *buffer)
+ void *buffer, int relocatable, grub_uint32_t min_addr,
+ grub_uint32_t max_addr, grub_size_t align, grub_uint32_t preference,
+ grub_uint32_t *base_addr, int avoid_efi_boot_services)
{
if (grub_multiboot_is_elf32 (buffer))
- return grub_multiboot_load_elf32 (file, filename, buffer);
+ return grub_multiboot_load_elf32 (file, filename, buffer, relocatable,
+ min_addr, max_addr, align, preference,
+ base_addr, avoid_efi_boot_services);
else if (grub_multiboot_is_elf64 (buffer))
- return grub_multiboot_load_elf64 (file, filename, buffer);
+ return grub_multiboot_load_elf64 (file, filename, buffer, relocatable,
+ min_addr, max_addr, align, preference,
+ base_addr, avoid_efi_boot_services);
return grub_error (GRUB_ERR_UNKNOWN_OS, N_("invalid arch-dependent ELF magic"));
}
diff --git a/grub-core/loader/multiboot_elfxx.c b/grub-core/loader/multiboot_elfxx.c
index e3a39b6..0c01569 100644
--- a/grub-core/loader/multiboot_elfxx.c
+++ b/grub-core/loader/multiboot_elfxx.c
@@ -51,7 +51,10 @@ CONCAT(grub_multiboot_is_elf, XX) (void *buffer)
}
static grub_err_t
-CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file, const char *filename, void *buffer)
+CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file, const char *filename,
+ void *buffer, int relocatable, grub_uint32_t min_addr,
+ grub_uint32_t max_addr, grub_size_t align, grub_uint32_t preference,
+ grub_uint32_t *base_addr, int avoid_efi_boot_services)
{
Elf_Ehdr *ehdr = (Elf_Ehdr *) buffer;
char *phdr_base;
@@ -89,19 +92,30 @@ CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file, const char *filename, voi
if (phdr(i)->p_paddr + phdr(i)->p_memsz > highest_load)
highest_load = phdr(i)->p_paddr + phdr(i)->p_memsz;
- grub_dprintf ("multiboot_loader", "segment %d: paddr=0x%lx, memsz=0x%lx, vaddr=0x%lx\n",
- i, (long) phdr(i)->p_paddr, (long) phdr(i)->p_memsz, (long) phdr(i)->p_vaddr);
+ grub_dprintf ("multiboot_loader", "segment %d: paddr=0x%lx, memsz=0x%lx, vaddr=0x%lx,"
+ "align=0x%lx, relocatable=%d, avoid_efi_boot_services=%d\n", i,
+ (long) phdr(i)->p_paddr, (long) phdr(i)->p_memsz, (long) phdr(i)->p_vaddr,
+ (long) align, relocatable, avoid_efi_boot_services);
{
grub_relocator_chunk_t ch;
- err = grub_relocator_alloc_chunk_addr (grub_multiboot_relocator,
- &ch, phdr(i)->p_paddr,
- phdr(i)->p_memsz);
+
+ if (relocatable)
+ err = grub_relocator_alloc_chunk_align (grub_multiboot_relocator, &ch,
+ min_addr, max_addr - phdr(i)->p_memsz,
+ phdr(i)->p_memsz, align ? align : 1,
+ preference, avoid_efi_boot_services);
+ else
+ err = grub_relocator_alloc_chunk_addr (grub_multiboot_relocator,
+ &ch, phdr(i)->p_paddr,
+ phdr(i)->p_memsz);
if (err)
{
grub_dprintf ("multiboot_loader", "Error loading phdr %d\n", i);
return err;
}
+ if (base_addr)
+ *base_addr = get_physical_target_address (ch);
source = get_virtual_current_address (ch);
}
@@ -208,7 +222,7 @@ CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file, const char *filename, voi
+ 1, sh->sh_size,
sh->sh_addralign,
GRUB_RELOCATOR_PREFERENCE_NONE,
- 0);
+ avoid_efi_boot_services);
if (err)
{
grub_dprintf ("multiboot_loader", "Error loading shdr %d\n", i);
diff --git a/grub-core/loader/multiboot_mbi2.c b/grub-core/loader/multiboot_mbi2.c
index ce68f48..03725a1 100644
--- a/grub-core/loader/multiboot_mbi2.c
+++ b/grub-core/loader/multiboot_mbi2.c
@@ -68,6 +68,7 @@ static grub_size_t elf_sec_num, elf_sec_entsize;
static unsigned elf_sec_shstrndx;
static void *elf_sections;
static int keep_bs = 0;
+static grub_uint32_t base_addr = 0;
void
grub_multiboot_add_elfsyms (grub_size_t num, grub_size_t entsize,
@@ -107,11 +108,14 @@ grub_multiboot_load (grub_file_t file, const char *filename)
grub_err_t err;
struct multiboot_header_tag *tag;
struct multiboot_header_tag_address *addr_tag = NULL;
- int entry_specified = 0, efi_entry_specified = 0;
+ struct multiboot_header_tag_relocatable *rel_tag;
+ int entry_specified = 0, efi_entry_specified = 0, relocatable = 0;
grub_addr_t entry = 0, efi_entry = 0;
- grub_uint32_t console_required = 0;
+ grub_uint32_t console_required = 0, min_addr = 0;
+ grub_uint32_t max_addr = 0, preference = GRUB_RELOCATOR_PREFERENCE_NONE;
struct multiboot_header_tag_framebuffer *fbtag = NULL;
int accepted_consoles = GRUB_MULTIBOOT_CONSOLE_EGA_TEXT;
+ grub_size_t align = 0;
buffer = grub_malloc (MULTIBOOT_SEARCH);
if (!buffer)
@@ -174,6 +178,7 @@ grub_multiboot_load (grub_file_t file, const char *filename)
case MULTIBOOT_TAG_TYPE_EFI_BS:
case MULTIBOOT_TAG_TYPE_EFI32_IH:
case MULTIBOOT_TAG_TYPE_EFI64_IH:
+ case MULTIBOOT_TAG_TYPE_BASE_ADDR:
break;
default:
@@ -215,6 +220,27 @@ grub_multiboot_load (grub_file_t file, const char *filename)
accepted_consoles |= GRUB_MULTIBOOT_CONSOLE_FRAMEBUFFER;
break;
+ case MULTIBOOT_HEADER_TAG_RELOCATABLE:
+ relocatable = 1;
+ rel_tag = (struct multiboot_header_tag_relocatable *) tag;
+ min_addr = rel_tag->min_addr;
+ max_addr = rel_tag->max_addr;
+ align = rel_tag->align;
+ switch (rel_tag->preference)
+ {
+ case MULTIBOOT_LOAD_PREFERENCE_LOW:
+ preference = GRUB_RELOCATOR_PREFERENCE_LOW;
+ break;
+
+ case MULTIBOOT_LOAD_PREFERENCE_HIGH:
+ preference = GRUB_RELOCATOR_PREFERENCE_HIGH;
+ break;
+
+ default:
+ preference = GRUB_RELOCATOR_PREFERENCE_NONE;
+ }
+ break;
+
/* GRUB always page-aligns modules. */
case MULTIBOOT_HEADER_TAG_MODULE_ALIGN:
break;
@@ -260,15 +286,22 @@ grub_multiboot_load (grub_file_t file, const char *filename)
else
code_size = load_size;
- err = grub_relocator_alloc_chunk_addr (grub_multiboot_relocator,
- &ch, load_addr,
- code_size);
+ if (relocatable)
+ err = grub_relocator_alloc_chunk_align (grub_multiboot_relocator, &ch,
+ min_addr, max_addr - code_size,
+ code_size, align ? align : 1,
+ preference, keep_bs);
+ else
+ err = grub_relocator_alloc_chunk_addr (grub_multiboot_relocator,
+ &ch, load_addr,
+ code_size);
if (err)
{
grub_dprintf ("multiboot_loader", "Error loading aout kludge\n");
grub_free (buffer);
return err;
}
+ base_addr = get_physical_target_address (ch);
source = get_virtual_current_address (ch);
if ((grub_file_seek (file, offset)) == (grub_off_t) -1)
@@ -290,7 +323,9 @@ grub_multiboot_load (grub_file_t file, const char *filename)
}
else
{
- err = grub_multiboot_load_elf (file, filename, buffer);
+ err = grub_multiboot_load_elf (file, filename, buffer,
+ relocatable, min_addr, max_addr,
+ align, preference, &base_addr, keep_bs);
if (err)
{
grub_free (buffer);
@@ -303,6 +338,14 @@ grub_multiboot_load (grub_file_t file, const char *filename)
else if (entry_specified)
grub_multiboot_payload_eip = entry;
+ if (relocatable)
+ {
+ if (base_addr > min_addr)
+ grub_multiboot_payload_eip += base_addr - min_addr;
+ else
+ grub_multiboot_payload_eip -= min_addr - base_addr;
+ }
+
Why is it relative to min_addr? Sounds like it should be just an offset from base addr. What do ET_DYN files use?
if (fbtag)
err = grub_multiboot_set_console (GRUB_MULTIBOOT_CONSOLE_FRAMEBUFFER,
accepted_consoles,
@@ -409,6 +452,7 @@ grub_multiboot_get_mbi_size (void)
+ grub_get_multiboot_mmap_count ()
* sizeof (struct multiboot_mmap_entry)), MULTIBOOT_TAG_ALIGN)
+ ALIGN_UP (sizeof (struct multiboot_tag_framebuffer), MULTIBOOT_TAG_ALIGN)
+ + ALIGN_UP (sizeof (struct multiboot_tag_base_addr), MULTIBOOT_TAG_ALIGN)
#ifdef GRUB_MACHINE_EFI
#ifdef __i386__
+ ALIGN_UP (sizeof (struct multiboot_tag_efi32), MULTIBOOT_TAG_ALIGN)
@@ -698,6 +742,15 @@ grub_multiboot_make_mbi (grub_uint32_t *target)
ptrorig += (2 * sizeof (grub_uint32_t)) / sizeof (grub_properly_aligned_t);
{
+ struct multiboot_tag_base_addr *tag = (struct multiboot_tag_base_addr *) ptrorig;
+ tag->type = MULTIBOOT_TAG_TYPE_BASE_ADDR;
+ tag->size = sizeof (struct multiboot_tag_base_addr);
+ tag->base_addr = base_addr;
+ ptrorig += ALIGN_UP (tag->size, MULTIBOOT_TAG_ALIGN)
+ / sizeof (grub_properly_aligned_t);
+ }
+
+ {
struct multiboot_tag_string *tag = (struct multiboot_tag_string *) ptrorig;
tag->type = MULTIBOOT_TAG_TYPE_CMDLINE;
tag->size = sizeof (struct multiboot_tag_string) + cmdline_size;
diff --git a/include/grub/multiboot.h b/include/grub/multiboot.h
index e13c084..ec322b0 100644
--- a/include/grub/multiboot.h
+++ b/include/grub/multiboot.h
@@ -94,7 +94,9 @@ grub_multiboot_load (grub_file_t file, const char *filename);
/* Load ELF32 or ELF64. */
grub_err_t
grub_multiboot_load_elf (grub_file_t file, const char *filename,
- void *buffer);
+ void *buffer, int relocatable, grub_uint32_t min_addr,
+ grub_uint32_t max_addr, grub_size_t align, grub_uint32_t preference,
+ grub_uint32_t *base_addr, int avoid_efi_boot_services);
extern grub_size_t grub_multiboot_pure_size;
extern grub_size_t grub_multiboot_alloc_mbi;
extern grub_uint32_t grub_multiboot_payload_eip;
diff --git a/include/multiboot2.h b/include/multiboot2.h
index 36a174f..c09bdbc 100644
--- a/include/multiboot2.h
+++ b/include/multiboot2.h
@@ -62,6 +62,7 @@
#define MULTIBOOT_TAG_TYPE_EFI_BS 18
#define MULTIBOOT_TAG_TYPE_EFI32_IH 19
#define MULTIBOOT_TAG_TYPE_EFI64_IH 20
+#define MULTIBOOT_TAG_TYPE_BASE_ADDR 21
#define MULTIBOOT_HEADER_TAG_END 0
#define MULTIBOOT_HEADER_TAG_INFORMATION_REQUEST 1
@@ -72,11 +73,16 @@
#define MULTIBOOT_HEADER_TAG_MODULE_ALIGN 6
#define MULTIBOOT_HEADER_TAG_EFI_BS 7
#define MULTIBOOT_HEADER_TAG_ENTRY_ADDRESS_EFI64 9
+#define MULTIBOOT_HEADER_TAG_RELOCATABLE 10
#define MULTIBOOT_ARCHITECTURE_I386 0
#define MULTIBOOT_ARCHITECTURE_MIPS32 4
#define MULTIBOOT_HEADER_TAG_OPTIONAL 1
+#define MULTIBOOT_LOAD_PREFERENCE_NONE 0
+#define MULTIBOOT_LOAD_PREFERENCE_LOW 1
+#define MULTIBOOT_LOAD_PREFERENCE_HIGH 2
+
#define MULTIBOOT_CONSOLE_FLAGS_CONSOLE_REQUIRED 1
#define MULTIBOOT_CONSOLE_FLAGS_EGA_TEXT_SUPPORTED 2
@@ -161,6 +167,17 @@ struct multiboot_header_tag_module_align
multiboot_uint32_t size;
};
+struct multiboot_header_tag_relocatable
+{
+ multiboot_uint16_t type;
+ multiboot_uint16_t flags;
+ multiboot_uint32_t size;
+ multiboot_uint32_t min_addr;
+ multiboot_uint32_t max_addr;
+ multiboot_uint32_t align;
+ multiboot_uint32_t preference;
+};
+
struct multiboot_color
{
multiboot_uint8_t red;
@@ -387,6 +404,13 @@ struct multiboot_tag_efi64_ih
multiboot_uint64_t pointer;
};
+struct multiboot_tag_base_addr
+{
+ multiboot_uint32_t type;
+ multiboot_uint32_t size;
+ multiboot_uint32_t base_addr;
+};
+
#endif /* ! ASM_FILE */
#endif /* ! MULTIBOOT_HEADER */
--
1.7.10.4
--
Regards
Vladimir 'phcoder' Serbinenko
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