I've come across some problems with the assembly version of the ELFNOTE
macro currently in -mm. (in
x86-put-note-sections-into-a-pt_note-segment-in-vmlinux.patch)
The first is that older gas does not support :varargs in .macro
definitions (in my testing 2.17 does while 2.15 does not, I don't know
when it became supported). The Changes file says binutils >= 2.12 so I
think we need to avoid using it. There are no other uses in mainline or
-mm. Old gas appears to just ignore it so you get "too many arguments"
type errors.
Secondly it seems that passing strings as arguments to assembler macros
is broken without varargs. It looks like they get unquoted or each
character is treated as a separate argument or something and this causes
all manner of grief. I think this is because of the use of -traditional
when compiling assembly files.
Therefore I have translated the assembler macro into a pre-processor
macro.
I added the desctype as a separate argument instead of including it with
the descdata as the previous version did since -traditional means the
ELFNOTE definition after the #else needs to have the same number of
arguments (I think so anyway, the -traditional CPP semantics are pretty
fscking strange!).
With this patch I am able to define elfnotes in assembly like this with
both old and new assemblers.
ELFNOTE(Xen, XEN_ELFNOTE_GUEST_OS, .asciz, "linux")
ELFNOTE(Xen, XEN_ELFNOTE_GUEST_VERSION, .asciz, "2.6")
ELFNOTE(Xen, XEN_ELFNOTE_XEN_VERSION, .asciz, "xen-3.0")
ELFNOTE(Xen, XEN_ELFNOTE_VIRT_BASE, .long, __PAGE_OFFSET)
Which seems reasonable enough.
Signed-off-by: Ian Campbell <[email protected]>
Acked-by: Jeremy Fitzhardinge <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This patch updates x86_64 linker script to pack any .note.* sections
into a PT_NOTE segment in the output file.
To do this, we tell ld that we need a PT_NOTE segment. This requires
us to start explicitly mapping sections to segments, so we also need
to explicitly create PT_LOAD segments for text and data, and map the
sections to them appropriately. Fortunately, each section will
default to its previous section's segment, so it doesn't take many
changes to vmlinux.lds.S.
The corresponding change is already made for i386 in -mm and I'd like
this patch to join it. The section to segment mappings do change as do
the segment flags so some time in -mm would be good for that reason as
well, just in case.
In particular .data and .bss move from the text segment to the data
segment and .data.cacheline_aligned .data.read_mostly are put in the
data segment instead of a separate one.
I think that it would be possible to exactly match the existing section
to segment mapping and flags but it would be a more intrusive change and
I'm not sure there is a reason for the existing layout other than it is
what you get by default if you don't explicitly specify something else.
If there is a reason for the existing layout then I will of course make
the more intrusive change. If there is no reason we could probably drop
the executable or writable flags from some segments but I don't know how
much attention is paid to them anyway so it might not be worth the
effort.
The vsyscall related sections need to go in a different segment to the
normal data segment and so I invented a "user" segment to contain them.
I believe this should appear to be another data segment as far as the
kernel is concerned so the flags are setup accordingly.
The notes will be used in the Xen paravirt_ops backend to provide
additional information to the domain builder. I am in the process of
converting the xen-unstable kernels and tools over to this scheme at the
moment to support this in the future.
It has been suggested to me that the notes segment should have flags 0
(i.e. not readable) since it is only used by the loader and is not used
at runtime. For now I went with a readable segment since that is what
the i386 patch uses.
AK: dropped NOTES addition right now because the needed infrastructure
for that is not merged yet
Signed-off-by: Ian Campbell <[email protected]>
Signed-off-by: Andi Kleen <[email protected]>
Ian Campbell