Putting the vvar area after the vdso text is rather complicated: it
only works of the total length of the vdso text mapping is known at
vdso link time, and the linker doesn't allow symbol addresses to
depend on the sizes of non-allocatable data after the PT_LOAD
segment.
Moving the vvar area before the vdso text will allow is to safely
map non-allocatable data after the vdso text, which is a nice
simplification.
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/156c78c0d93144ff1055a66493783b9e56813983.1405040914.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
.data doesn't need to be separate from .rodata: they're both readonly.
.altinstructions and .altinstr_replacement aren't needed by anything
except vdso2c; strip them from the final image.
While we're at it, rather than aligning the actual executable text,
just shove some unused-at-runtime data in between real data and
text.
My vdso image is still above 4k, but I'm disinclined to try to
trim it harder for 3.16. For future trimming, I suspect that these
sections could be moved to later in the file and dropped from
the in-memory image:
.gnu.version and .gnu.version_d (this may lose versions in gdb)
.eh_frame (should be harmless)
.eh_frame_hdr (I'm not really sure)
.hash (AFAIK nothing needs this section header)
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/2e96d0c49016ea6d026a614ae645e93edd325961.1403129369.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Fully stripping the vDSO has other unfortunate side effects:
- binutils is unable to find ELF notes without a SHT_NOTE section.
- Even elfutils has trouble: it can find ELF notes without a section
table at all, but if a section table is present, it won't look for
PT_NOTE.
- gdb wants section names to match between stripped DSOs and their
symbols; otherwise it will corrupt symbol addresses.
We're also breaking the rules: section 0 is supposed to be SHT_NULL.
Fix these problems by building a better fake section table. While
we're at it, we might as well let buggy Go versions keep working well
by giving the SHT_DYNSYM entry the correct size.
This is a bit unfortunate: it adds quite a bit of size to the vdso
image.
If/when binutils improves and the improved versions become widespread,
it would be worth considering dropping most of this.
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/0e546a5eeaafdf1840e6ee654a55c1e727c26663.1403129369.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This unifies the vdso mapping code and teaches it how to map special
pages at addresses corresponding to symbols in the vdso image. The
new code is used for all vdso variants, but so far only the 32-bit
variants use the new vvar page position.
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/b6d7858ad7b5ac3fd3c29cab6d6d769bc45d195e.1399317206.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
The .discard/.discard.* sections are used to generate intermediate
results for the assembler (effectively "test assembly".) The output
is waste and should not be retained.
Cc: Stefani Seibold <stefani@seibold.net>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/n/tip-psizrnant8x3nrhbgvq2vekr@git.kernel.org
This patch add the time support for 32 bit a VDSO to a 32 bit kernel.
For 32 bit programs running on a 32 bit kernel, the same mechanism is
used as for 64 bit programs running on a 64 bit kernel.
Reviewed-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Stefani Seibold <stefani@seibold.net>
Link: http://lkml.kernel.org/r/1395094933-14252-10-git-send-email-stefani@seibold.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
The compat vDSO is a complicated hack that's needed to maintain
compatibility with a small range of glibc versions.
This removes it and replaces it with a much simpler hack: a config
option to disable the 32-bit vDSO by default.
This also changes the default value of CONFIG_COMPAT_VDSO to n --
users configuring kernels from scratch almost certainly want that
choice.
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/4bb4690899106eb11430b1186d5cc66ca9d1660c.1394751608.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This revamps the vDSO linker script to lay things out with the best
packing of the data and good, separate alignment of the code. The
rigid layout using VDSO_TEXT_OFFSET no longer matters to the kernel.
I've moved the layout parts of the linker script into a new include
file, vdso-layout.lds.S; this is in preparation for sharing the script
for the 32-bit vDSO builds too.
Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
