Josh Triplett
2013-Mar-27 21:50 UTC
[syslinux] [PATCH] Fix support for Linux kernel images with no protected mode code
Some kernel images use the Linux kernel boot protocol and header
structure, but do not actually have any protected-mode code. For
instance, grub's 1024-byte lnxboot.img consists of 1024 real-mode bytes
and 0 protected-mode bytes; you can concatenate it with a full grub
core.img to produce a self-contained bootable kernel, but you can also
use it standalone as the kernel with the core.img loaded as an initrd.
syslinux 4 supports this, but it no longer works with syslinux 5: the
memmap functions do not correctly handle a request to work with a 0-byte
region. With lnxboot.img, this would cause syslinux to bail because it
thinks it has no space at the 1M load location but cannot relocate
lnxboot.img. (In bailing, it gives the confusing error message "Bad
file descriptor", not because that error actually occurred when
attempting to boot the kernel, but because errno has that value on entry
to syslinux_boot_linux and nothing clears or sets it.)
Fix the regression by handling the corner case of no protected-mode code
explicitly.
Signed-off-by: Josh Triplett <josh at joshtriplett.org>
Signed-off-by: Burt Triplett <burt at pbjtriplett.org>
---
This patch applies to the "elflink" branch for syslinux 5.
Found because people started trying to use syslinux 5 to boot BITS,
which uses lnxboot.img as kernel and core.img as initrd, and it failed
to boot with the mysterious "Bad file descriptor" message mentioned
above.
com32/lib/syslinux/load_linux.c | 18 +++++++++++-------
1 files changed, 11 insertions(+), 7 deletions(-)
diff --git a/com32/lib/syslinux/load_linux.c b/com32/lib/syslinux/load_linux.c
index 471d8a5..04a5210 100644
--- a/com32/lib/syslinux/load_linux.c
+++ b/com32/lib/syslinux/load_linux.c
@@ -324,7 +324,8 @@ int syslinux_boot_linux(void *kernel_buf, size_t
kernel_size,
/* Place the kernel in memory */
/* First, find a suitable place for the protected-mode code */
- if (syslinux_memmap_type(amap, prot_mode_base, prot_mode_size)
+ if (prot_mode_size &&
+ syslinux_memmap_type(amap, prot_mode_base, prot_mode_size)
!= SMT_FREE) {
const struct syslinux_memmap *mp;
if (!hdr.relocatable_kernel)
@@ -423,12 +424,15 @@ int syslinux_boot_linux(void *kernel_buf, size_t
kernel_size,
}
/* Protected-mode code */
- if (syslinux_add_movelist(&fraglist, prot_mode_base,
- (addr_t) kernel_buf + real_mode_size,
- prot_mode_size))
- goto bail;
- if (syslinux_add_memmap(&amap, prot_mode_base, prot_mode_size,
SMT_ALLOC))
- goto bail;
+ if (prot_mode_size) {
+ if (syslinux_add_movelist(&fraglist, prot_mode_base,
+ (addr_t) kernel_buf + real_mode_size,
+ prot_mode_size))
+ goto bail;
+ if (syslinux_add_memmap(&amap, prot_mode_base, prot_mode_size,
+ SMT_ALLOC))
+ goto bail;
+ }
/* Figure out the size of the initramfs, and where to put it.
We should put it at the highest possible address which is
--
1.7.2.5
Matt Fleming
2013-Apr-03 11:13 UTC
[syslinux] [PATCH] Fix support for Linux kernel images with no protected mode code
On 27/03/13 21:50, Josh Triplett wrote:> Some kernel images use the Linux kernel boot protocol and header > structure, but do not actually have any protected-mode code. For > instance, grub's 1024-byte lnxboot.img consists of 1024 real-mode bytes > and 0 protected-mode bytes; you can concatenate it with a full grub > core.img to produce a self-contained bootable kernel, but you can also > use it standalone as the kernel with the core.img loaded as an initrd. > > syslinux 4 supports this, but it no longer works with syslinux 5: the > memmap functions do not correctly handle a request to work with a 0-byte > region. With lnxboot.img, this would cause syslinux to bail because it > thinks it has no space at the 1M load location but cannot relocate > lnxboot.img. (In bailing, it gives the confusing error message "Bad > file descriptor", not because that error actually occurred when > attempting to boot the kernel, but because errno has that value on entry > to syslinux_boot_linux and nothing clears or sets it.) > > Fix the regression by handling the corner case of no protected-mode code > explicitly. > > Signed-off-by: Josh Triplett <josh at joshtriplett.org> > Signed-off-by: Burt Triplett <burt at pbjtriplett.org> > --- > > This patch applies to the "elflink" branch for syslinux 5.Looks good to me. I'll apply it unless Peter has any objections.> Found because people started trying to use syslinux 5 to boot BITS, > which uses lnxboot.img as kernel and core.img as initrd, and it failed > to boot with the mysterious "Bad file descriptor" message mentioned > above.Oh yeah, that old chestnut. I'll fix that up. Thanks! -- Matt Fleming, Intel Open Source Technology Center