Update fixes for exported symbol versions
Linus has re-enable CONFIG_MODVERSIONS, but also weakened the version matching. Apply his match but then revert the weakening. Also add a proposed fix for missing version CRCs, which gives them a default value of zero. Since buildcheck.py now checks for this, we should detect all unversioned symbols at build time.
This commit is contained in:
Ben Hutchings
parent
8789780466
commit
2431e89ed3
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@ -16,7 +16,9 @@ linux (4.9~rc7-1~exp1) UNRELEASED; urgency=medium
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- [x86] kbuild: enable modversions for symbols exported from assembly
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- [powerpc] Remove Mac-on-Linux hooks
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- [powerpc*] Fix missing CRCs, add yet more asm-prototypes.h declarations
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- Revert "Fix subtle CONFIG_MODVERSIONS problems"
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- Re-enable CONFIG_MODVERSIONS in a slightly weaker form
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- default exported asm symbols to zero
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- module: Disable matching missing version CRC
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* debian/bin/buildcheck.py: Add check for symbols with version CRC of 0
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-- Uwe Kleine-König <ukleinek@debian.org> Thu, 17 Nov 2016 09:55:16 +0100
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@ -0,0 +1,32 @@
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From: Arnd Bergmann <arnd@arndb.de>
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Date: Fri, 02 Dec 2016 13:40:27 +0100
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Subject: default exported asm symbols to zero
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Origin: https://lkml.kernel.org/r/8452191.39CeLIHTBT@wuerfel
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With binutils-2.16 and before, a weak missing symbol was kept during the
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final link, and a missing CRC for an export would lead to that CRC
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being treated as zero implicitly. With binutils-2.17, the crc
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symbol gets dropped, and any module trying to use it will fail to
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load.
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This sets the weak CRC symbol to zero explicitly, making it defined
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in vmlinux, which in turn lets us load the modules referring to
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that CRC.
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The comment above the __CRC_SYMBOL macro suggests that this was
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always the intention, although it also seems that all symbols
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defined in C have a correct CRC these days, and only the exports
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that are now done in assembly need this.
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Signed-off-by: Arnd Bergmann <arnd@arndb.de>
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---
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--- a/include/asm-generic/export.h
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+++ b/include/asm-generic/export.h
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@@ -54,6 +54,7 @@ KSYM(__kstrtab_\name):
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KSYM(__kcrctab_\name):
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__put KSYM(__crc_\name)
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.weak KSYM(__crc_\name)
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+ .set KSYM(__crc_\name), 0
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.previous
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#endif
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#endif
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@ -0,0 +1,23 @@
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From: Ben Hutchings <ben@decadent.org.uk>
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Date: Fri, 02 Dec 2016 23:06:18 +0000
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Subject: module: Disable matching missing version CRC
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Forwarded: not-needed
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This partly reverts commit cd3caefb4663e3811d37cc2afad3cce642d60061.
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We want to fail closed if a symbol version CRC is missing, as the
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alternative may allow subverting module signing.
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---
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--- a/kernel/module.c
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+++ b/kernel/module.c
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@@ -1301,9 +1301,8 @@ static int check_version(Elf_Shdr *sechd
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goto bad_version;
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}
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- /* Broken toolchain. Warn once, then let it go.. */
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- pr_warn_once("%s: no symbol version for %s\n", mod->name, symname);
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- return 1;
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+ pr_warn("%s: no symbol version for %s\n", mod->name, symname);
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+ return 0;
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bad_version:
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pr_warn("%s: disagrees about version of symbol %s\n",
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57
debian/patches/bugfix/all/re-enable-config_modversions-in-a-slightly-weaker-fo.patch
vendored
Normal file
57
debian/patches/bugfix/all/re-enable-config_modversions-in-a-slightly-weaker-fo.patch
vendored
Normal file
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@ -0,0 +1,57 @@
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From: Linus Torvalds <torvalds@linux-foundation.org>
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Date: Tue, 29 Nov 2016 15:20:14 -0800
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Subject: Re-enable CONFIG_MODVERSIONS in a slightly weaker form
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Origin: https://git.kernel.org/linus/faaae2a581435f32781a105dda3501df388fddcb
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This enables CONFIG_MODVERSIONS again, but allows for missing symbol CRC
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information in order to work around the issue that newer binutils
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versions seem to occasionally drop the CRC on the floor. binutils 2.26
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seems to work fine, while binutils 2.27 seems to break MODVERSIONS of
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symbols that have been defined in assembler files.
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[ We've had random missing CRC's before - it may be an old problem that
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just is now reliably triggered with the weak asm symbols and a new
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version of binutils ]
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Some day I really do want to remove MODVERSIONS entirely. Sadly, today
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does not appear to be that day: Debian people apparently do want the
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option to enable MODVERSIONS to make it easier to have external modules
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across kernel versions, and this seems to be a fairly minimal fix for
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the annoying problem.
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Cc: Ben Hutchings <ben@decadent.org.uk>
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Acked-by: Michal Marek <mmarek@suse.com>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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init/Kconfig | 1 -
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kernel/module.c | 5 +++--
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2 files changed, 3 insertions(+), 3 deletions(-)
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diff --git a/init/Kconfig b/init/Kconfig
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index c4fbc1e55c25..34407f15e6d3 100644
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--- a/init/Kconfig
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+++ b/init/Kconfig
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@@ -1945,7 +1945,6 @@ config MODULE_FORCE_UNLOAD
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config MODVERSIONS
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bool "Module versioning support"
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- depends on BROKEN
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help
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Usually, you have to use modules compiled with your kernel.
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Saying Y here makes it sometimes possible to use modules
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diff --git a/kernel/module.c b/kernel/module.c
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index f57dd63186e6..0e54d5bf0097 100644
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--- a/kernel/module.c
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+++ b/kernel/module.c
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@@ -1301,8 +1301,9 @@ static int check_version(Elf_Shdr *sechdrs,
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goto bad_version;
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}
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- pr_warn("%s: no symbol version for %s\n", mod->name, symname);
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- return 0;
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+ /* Broken toolchain. Warn once, then let it go.. */
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+ pr_warn_once("%s: no symbol version for %s\n", mod->name, symname);
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+ return 1;
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bad_version:
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pr_warn("%s: disagrees about version of symbol %s\n",
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@ -1,60 +0,0 @@
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From: Ben Hutchings <ben@decadent.org.uk>
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Date: Fri, 2 Dec 2016 00:07:04 +0000
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Subject: Revert "Fix subtle CONFIG_MODVERSIONS problems"
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This reverts commit cd3caefb4663e3811d37cc2afad3cce642d60061.
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On Fri, 2016-11-25 at 10:01 -0800, Linus Torvalds wrote:
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[...]
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> > What else do people *actually* use it for? Preventing mismatched modules
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> > when .git version is not attached and release version of the kernel has
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> > not been bumped. Is that it?
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>
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> It used to be very useful for avoiding loading stale modules and then
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> wasting days on debugging something that wasn't the case when you had
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> forgotten to do "make modules_install". Change some subtle internal
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> ABI issue (add/remove a parameter, whatever) and it would really help.
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>
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> These days, for me, LOCALVERSION_AUTO and module signing are what I
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> personally tend to use.
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>
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> The modversions stuff may just be too painful to bother with. Very few
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> people probably use it, and the ones that do likely don't have any
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> overriding reason why.
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[...]
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Debian has some strong reasons:
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1. Changing the release string requires any out-of-tree modules to be
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upgraded (at least rebuilt) on end-user systems. So we try to avoid
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doing that during the lifetime of a stable release, i.e. we don't let
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the release string change. Also, the release string is reflected in
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package names (e.g. linux-image-4.8.0-1-amd64), and introducing new
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package names requires manual approval by the Debian archive team.
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2. We want to allow ABI breaks for "internal" symbols used only by in-
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tree modules, as those breaks will be resolved by rebooting to complete
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the upgrade. But we need a run-time check to prevent loading an
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incompatible module before the reboot.
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3. So far as I can see, module signing doesn't work for a distribution
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kernel with out-of-tree modules as there has to be a trust path from a
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built-in certificate to the module signing certificate. So signature
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enforcement will have to be disabled on systems that use out-of-tree
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modules, thus it's not a substitute for modversions.
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---
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init/Kconfig | 1 -
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1 file changed, 1 deletion(-)
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diff --git a/init/Kconfig b/init/Kconfig
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index c4fbc1e55c25..34407f15e6d3 100644
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--- a/init/Kconfig
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+++ b/init/Kconfig
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@@ -1945,7 +1945,6 @@ config MODULE_FORCE_UNLOAD
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config MODVERSIONS
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bool "Module versioning support"
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- depends on BROKEN
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help
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Usually, you have to use modules compiled with your kernel.
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Saying Y here makes it sometimes possible to use modules
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@ -102,7 +102,9 @@ bugfix/alpha/revert-alpha-move-exports-to-actual-definitions.patch
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bugfix/x86/x86-kbuild-enable-modversions-for-symbols-exported-f.patch
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bugfix/powerpc/powerpc-remove-mac-on-linux-hooks.patch
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bugfix/powerpc/powerpc-fix-missing-crcs-add-yet-more-asm-prototypes.patch
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bugfix/all/revert-fix-subtle-config_modversions-problems.patch
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bugfix/all/re-enable-config_modversions-in-a-slightly-weaker-fo.patch
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bugfix/all/default-exported-asm-symbols-to-zero.patch
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bugfix/all/module-disable-matching-missing-version-crc.patch
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# ABI maintenance
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