Re: Would a cleanup+extending of docs/multiboot.h be acceptable?

[Goswin von Brederlow <goswin-v-b@web.de>]

"Vladimir 'φ-coder/phcoder' Serbinenko" <phcoder@gmail.com> writes:

> On 07.04.2011 16:50, Goswin von Brederlow wrote:
>> "Vladimir 'φ-coder/phcoder' Serbinenko" <phcoder@gmail.com> writes:
>>
>>> On 07.04.2011 14:09, Goswin von Brederlow wrote:
>>>> Hi,
>>>>
>>>> I've been working on a 32bit->64bit trampoline based on the example
>>>> kernel that just switches to 64bit mode and executes a real kernel
>>>> passed as module. As real kernel I want to use grubs example kernel as
>>>> well to just verify the multiboot infos passed through the trampoline
>>>> are intact.
>>> Please don't use outdated code as base. Now we work on multiboot2 and
>> I've seen multiboot2 mentioned but I can't find specs for it. What I
>> did find are the "Multiboot Specification version 0.6.96" [1]
>>
>> So where is this multiboot2?
>>
> Latest multiboot1 (cleanups) is at
> http://bzr.savannah.gnu.org/r/grub/trunk/multiboot/

Ok, this is much cleaner than what is in the grub source in Debian already.

Remaining issues:

1) hardcoded bit numbers:

/* Check if the bit BIT in FLAGS is set.  */
#define CHECK_FLAG(flags,bit)   ((flags) & (1 << (bit)))
...
/* Are mem_* valid?  */
if (CHECK_FLAG (mbi->flags, 0))

The multiboot.h does not define the bit numbers, only masks for each
bit. Maybe this could be changed to

In multiboot.h add:

  #define MULTIBOOT_INFO_MEMORY_BIT 0

In kernel.c:

/* Check if the bit BIT in FLAGS is set.  */
#define CHECK_FLAG(flags,bit)   ((flags) & (1 << (MULTIBOOT_INFO_##bit##_BIT)))
...
/* Are mem_* valid?  */
if (CHECK_FLAG (mbi->flags, MEMORY))


2) Wrong types

  void cmain (unsigned long magic, unsigned long addr);
  static void itoa (char *buf, int base, int d);

should be:

  void cmain (multiboot_uint32_t magic, multiboot_uint32_t addr);
  static void itoa (char *buf, char base, int d);

All occurances of '(unsigned)' should be '(multiboot_uint32_t)'.

3) Could we use 64bit types?

It might be nice to teach printf about '%llx' (or '%q' for quad word)
and add a 64bit itoa. And maybe add a '%p' which would be 64bit in
64bit code and 32bit in 32bit code while '%x' is allways 32bit.

> Multiboot2 is at http://bzr.savannah.gnu.org/r/grub/branches/multiboot2/

I see that you have added 32bit MIPS support. No 64bit x86_64 support
though. So my trampoline + 64bit kernel stuff would still be interesting
to people.

The bigger problem though is the thing doesn't build or work:

1) ./autogen.sh

doc/Makefile.am:2: compiling `kernel.c' with per-target flags requires `AM_PROG_CC_C_O' in `configure.ac'

2) wrong source file

Making all in doc
make[2]: Entering directory `/home/mrvn/t/t/multiboot2/doc'
make[2]: *** No rule to make target `boot_mips.o', needed by `kernel'.  Stop.

There is only the boot.S, which is for x86. Fixing that:

3) -m32 missing

gcc -DHAVE_CONFIG_H -I. -I..     -DHAVE_CONFIG_H -I. -I..   -nostdlib -g -O2 -MT boot.o -MD -MP -MF .deps/boot.Tpo -c -o boot.o boot.S
boot.S: Assembler messages:
boot.S:97: Error: invalid instruction suffix for `push'
boot.S:101: Error: invalid instruction suffix for `push'
boot.S:103: Error: invalid instruction suffix for `push'
boot.S:109: Error: invalid instruction suffix for `push'
make[2]: *** [boot.o] Error 1

Note that the CFLAGS aren't used for the assembler file at all.

exporting CC="gcc -m32" to work around this.

4) typos in boot.S

--- doc/boot.S.orig     2011-04-07 18:58:41.000000000 +0200
+++ doc/boot.S  2011-04-07 18:58:59.000000000 +0200
@@ -50,11 +50,11 @@
        /* magic */
        .long   MULTIBOOT2_HEADER_MAGIC
        /* ISA: i386 */
-       .long   GRUB_MULTIBOOT_ARCHITECTURE_I386
+       .long   MULTIBOOT_ARCHITECTURE_I386
        /* Header length.  */
        .long   multiboot_header_end - multiboot_header
        /* checksum */
-       .long   -(MULTIBOOT2_HEADER_MAGIC + GRUB_MULTIBOOT_ARCHITECTURE_I386 + (multiboot_header_end - multiboot_header))
+       .long   -(MULTIBOOT2_HEADER_MAGIC + MULTIBOOT_ARCHITECTURE_I386 + (multiboot_header_end - multiboot_header))
 #ifndef __ELF__
 address_tag_start:
        .short MULTIBOOT_HEADER_TAG_ADDRESS


Ok, after all this I get:

% make
gcc -m32 -DHAVE_CONFIG_H -I. -I..     -DHAVE_CONFIG_H -I. -I..   -nostdlib -g -O2 -MT boot.o -MD -MP -MF .deps/boot.Tpo -c -o boot.o boot.S
gcc -m32 -DHAVE_CONFIG_H -I. -I..    -fno-builtin -nostdinc -O -g -Wall -imacros ../config.h -nostdlib -g -O2 -MT kernel-kernel.o -MD -MP -MF .deps/kernel-kernel.Tpo -c -o kernel-kernel.o `test -f 'kernel.c' || echo './'`kernel.c
gcc -m32 -fno-builtin -nostdinc -O -g -Wall -imacros ../config.h -nostdlib -g -O2 -nostdlib -Wl,-N -Wl,-Ttext -Wl,80100000 -Wl,--build-id=none  -o kernel boot.o kernel-kernel.o  

% file doc/kernel
doc/kernel: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically linked, not stripped

% kvm -m 64 -kernel doc/kernel
doesn't output anything, doesn't clear the screen.


And here I'm stuck. Everything looks alright.

I thought maybe the extra "-O2" screws something up. So I tried

doc% gcc -m32 -DHAVE_CONFIG_H -I. -I..     -DHAVE_CONFIG_H -I. -I..   -nostdlib -g -O -MT boot.o -MD -MP -MF .deps/boot.Tpo -c -o boot.o boot.S 

doc% gcc -m32 -DHAVE_CONFIG_H -I. -I..    -fno-builtin -nostdinc -O -g -Wall -imacros ../config.h -nostdlib -g -O -MT kernel-kernel.o -MD -MP -MF .deps/kernel-kernel.Tpo -c -o kernel-kernel.o `test -f 'kernel.c' || echo './'`kernel.c 

doc% gcc -m32 -fno-builtin -nostdinc -O -g -Wall -imacros ../config.h -nostdlib -g -O -nostdlib -Wl,-N -Wl,-Ttext -Wl,80100000 -Wl,--build-id=none  -o kernel boot.o kernel-kernel.o 

doc% kvm -m 64 -kernel kernel         
open /dev/kvm: No such file or directory
Could not initialize KVM, will disable KVM support
Failed to allocate memory: Cannot allocate memory
zsh: abort      kvm -m 64 -kernel kernel

It tries to allocate -0xE000 byte of memory, which is a few trillion
gazillion byte.


Trying the commands the old multiboot (from your first url) used to
build:

doc% gcc -DHAVE_CONFIG_H -I. -I..  -m32 -nostdlib -fno-builtin -nostdinc -O -g -Wall -imacros ../config.h   -DHAVE_CONFIG_H -I. -I..   -g -O2 -MT kernel-boot.o -MD -MP -MF .deps/kernel-boot.Tpo -c -o kernel-boot.o `test -f 'boot.S' || echo './'`boot.S

doc% gcc -DHAVE_CONFIG_H -I. -I..  -m32 -nostdlib -fno-builtin -nostdinc -O -g -Wall -imacros ../config.h   -g -O2 -MT kernel-kernel.o -MD -MP -MF .deps/kernel-kernel.Tpo -c -o kernel-kernel.o `test -f 'kernel.c' || echo './'`kernel.c

doc% gcc  -g -O2 -m32 -nostdlib -Wl,-N -Wl,-Ttext -Wl,100000 -Wl,--build-id=none  -o kernel kernel-boot.o kernel-kernel.o  

doc% kvm -m 64 -kernel kernel
doesn't output anything, doesn't clear the screen.

Any idea what is going wrong?

MfG
        Goswin