Re: [Qemu-stable] [Qemu-devel] [PATCH v2] multiboot: Fix bss segment support

[Anthony Liguori]

On 12/19/2011 11:35 AM, Alexander Graf wrote:
> On 24.07.2011, at 17:55, Göran Weinholt wrote:
>
> > Multiboot images can specify a bss segment. The boot loader must clear
> > the memory of the bss and ensure that no modules or structures are
> > allocated inside it. Several fields are provided in the Multiboot
> > header that were previously not used properly. The header is now used
> > to determine how much data should be read from the image and how much
> > memory should be reserved to the bss segment.
>
> This patch breaks the OSX booter:
>
>    http://people.exactcode.de/~rene/mac/boot

How is this licensed?  Is there source available?

> It now fails in fread(). Please revert this change for 1.0.1 and/or provide a 
> timely fix.

Is the patch incorrect in some way?  I don't see how it's reasonable to expect 
someone to fix a guest that cannot be legally run under QEMU.

If the patch is obviously incorrect, I'm all for reverting it, but I don't think 
we can reasonably ask people to debug OS X guest failures since OS X is clearly 
not allowed to run under QEMU.

Regards,

Anthony Liguori

> Alex
>
> > Signed-off-by: Göran Weinholt<address@hidden>
> > ---
> > hw/multiboot.c |   14 +++++++++-----
> > 1 files changed, 9 insertions(+), 5 deletions(-)
> >
> > diff --git a/hw/multiboot.c b/hw/multiboot.c
> > index 2426e84..a1d3f41 100644
> > --- a/hw/multiboot.c
> > +++ b/hw/multiboot.c
> > @@ -198,11 +198,14 @@ int load_multiboot(void *fw_cfg,
> >      } else {
> >          /* Valid if mh_flags sets MULTIBOOT_HEADER_HAS_ADDR. */
> >          uint32_t mh_header_addr = ldl_p(header+i+12);
> > +        uint32_t mh_load_end_addr = ldl_p(header+i+20);
> > +        uint32_t mh_bss_end_addr = ldl_p(header+i+24);
> >          mh_load_addr = ldl_p(header+i+16);
> >          uint32_t mb_kernel_text_offset = i - (mh_header_addr - mh_load_addr);
> > +        uint32_t mb_load_size = mh_load_end_addr - mh_load_addr;
> >
> >          mh_entry_addr = ldl_p(header+i+28);
> > -        mb_kernel_size = kernel_file_size - mb_kernel_text_offset;
> > +        mb_kernel_size = mh_bss_end_addr - mh_load_addr;
> >
> >          /* Valid if mh_flags sets MULTIBOOT_HEADER_HAS_VBE.
> >          uint32_t mh_mode_type = ldl_p(header+i+32);
> > @@ -212,17 +215,18 @@ int load_multiboot(void *fw_cfg,
> >
> >          mb_debug("multiboot: mh_header_addr = %#x\n", mh_header_addr);
> >          mb_debug("multiboot: mh_load_addr = %#x\n", mh_load_addr);
> > -        mb_debug("multiboot: mh_load_end_addr = %#x\n", ldl_p(header+i+20));
> > -        mb_debug("multiboot: mh_bss_end_addr = %#x\n", ldl_p(header+i+24));
> > +        mb_debug("multiboot: mh_load_end_addr = %#x\n", mh_load_end_addr);
> > +        mb_debug("multiboot: mh_bss_end_addr = %#x\n", mh_bss_end_addr);
> >          mb_debug("qemu: loading multiboot kernel (%#x bytes) at %#x\n",
> > -                 mb_kernel_size, mh_load_addr);
> > +                 mb_load_size, mh_load_addr);
> >
> >          mbs.mb_buf = qemu_malloc(mb_kernel_size);
> >          fseek(f, mb_kernel_text_offset, SEEK_SET);
> > -        if (fread(mbs.mb_buf, 1, mb_kernel_size, f) != mb_kernel_size) {
> > +        if (fread(mbs.mb_buf, 1, mb_load_size, f) != mb_load_size) {
> >              fprintf(stderr, "fread() failed\n");
> >              exit(1);
> >          }
> > +        memset(mbs.mb_buf + mb_load_size, 0, mb_kernel_size - mb_load_size);
> >          fclose(f);
> >      }
> >
> > --
> > 1.7.2.5