Alexander Graf <ag...@suse.de> writes: > On 19.12.2011, at 23:01, Anthony Liguori wrote: > > 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? > > Yes, it's the XNU booter, but binaries are easier to debug when it comes to > reading out the bootloader info: > > http://tgwbd.org/darwin/boot.html > > I don't know if the binary above is 1:1 built from those sources, but it's > definitely close enough.
I was unable to build that program from source, but I found a pre-built
binary that triggered the same bug. Please test the following patch.
Subject: [PATCH] multiboot: mh_load_end_addr and mh_bss_end_addr may be zero
There are two special cases in the address fields of the multiboot
format. If mh_load_end_addr is zero then the whole image file should
be loaded and if mh_bss_end_addr is zero then there is no bss segment.
With this change it is again possible to boot kernels where these
fields are zero.
Signed-off-by: Göran Weinholt <go...@weinholt.se>
---
hw/multiboot.c | 13 ++++++++++++-
1 files changed, 12 insertions(+), 1 deletions(-)
diff --git a/hw/multiboot.c b/hw/multiboot.c
index b4484a3..a43d56c 100644
--- a/hw/multiboot.c
+++ b/hw/multiboot.c
@@ -202,10 +202,21 @@ int load_multiboot(void *fw_cfg,
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;
+ uint32_t mb_load_size;
+
+ /* A load end address of zero indicates that the whole file
+ * should be loaded. */
+ if (!mh_load_end_addr)
+ mh_load_end_addr = kernel_file_size + mh_load_addr;
+
+ /* A bss end address of zero indicates that there is no bss
+ * segment. */
+ if (!mh_bss_end_addr)
+ mh_bss_end_addr = mh_load_end_addr;
mh_entry_addr = ldl_p(header+i+28);
mb_kernel_size = mh_bss_end_addr - mh_load_addr;
+ mb_load_size = mh_load_end_addr - mh_load_addr;
/* Valid if mh_flags sets MULTIBOOT_HEADER_HAS_VBE.
uint32_t mh_mode_type = ldl_p(header+i+32);
--
1.7.2.5
--
Göran Weinholt <go...@weinholt.se>
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