tag | 31f15042efe584ce737fdb16db4e6c01e55ff410 | |
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tagger | Todd Kjos <tkjos@google.com> | Mon Apr 26 09:56:18 2021 -0700 |
object | fef6bc00f5d5fbcea0bd696e936bc0e7e61c5516 |
android-mainline @ v5.12
commit | fef6bc00f5d5fbcea0bd696e936bc0e7e61c5516 | [log] [tgz] |
---|---|---|
author | Quentin Perret <qperret@google.com> | Thu Apr 08 18:01:05 2021 +0000 |
committer | Quentin Perret <qperret@google.com> | Mon Apr 26 08:51:09 2021 +0000 |
tree | 32bcbcf58cd6b51dd8df647980fafef3d7597473 | |
parent | c1b4f7d9ab16c1514cba53bba285dea7230eb38a [diff] |
FROMLIST: export: Make CRCs robust to symbol trimming The CRC calculation done by genksyms is triggered when the parser hits EXPORT_SYMBOL*() macros. At this point, genksyms recursively expands the types, and uses that as the input for the CRC calculation. In the case of forward-declared structs, the type expands to 'UNKNOWN'. Next, the result of the expansion of each type is cached, and is re-used when/if the same type is seen again for another exported symbol in the file. Unfortunately, this can cause CRC 'stability' issues when a struct definition becomes visible in the middle of a C file. For example, let's assume code with the following pattern: struct foo; int bar(struct foo *arg) { /* Do work ... */ } EXPORT_SYMBOL_GPL(bar); /* This contains struct foo's definition */ #include "foo.h" int baz(struct foo *arg) { /* Do more work ... */ } EXPORT_SYMBOL_GPL(baz); Here, baz's CRC will be computed using the expansion of struct foo that was cached after bar's CRC calculation ('UNKOWN' here). But if EXPORT_SYMBOL_GPL(bar) is removed from the file (because of e.g. symbol trimming using CONFIG_TRIM_UNUSED_KSYMS), struct foo will be expanded late, during baz's CRC calculation, which now has visibility over the full struct definition, hence resulting in a different CRC for baz. This can cause annoying issues for distro kernel (such as the Android Generic Kernel Image) which use CONFIG_UNUSED_KSYMS_WHITELIST. Indeed, as per the above, adding a symbol to the whitelist can change the CRC of symbols that are already kept exported. As such, modules built against a kernel with a trimmed ABI may not load against the same kernel built with an extended whitelist, even though they are still strictly binary compatible. While rebuilding the modules would obviously solve the issue, I believe this classifies as an odd genksyms corner case, and it gets in the way of kernel updates in the GKI context. To work around the issue, make sure to keep issuing the __GENKSYMS_EXPORT_SYMBOL macros for all trimmed symbols, hence making the genksyms parsing insensitive to symbol trimming. Bug: 184275771 Bug: 167230325 Signed-off-by: Quentin Perret <qperret@google.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Link: https://lore.kernel.org/r/20210408180105.2496212-1-qperret@google.com Change-Id: Id94085d446d5648943d4fe4f79e3177bc4f98093
BEST: Make all of your changes to upstream Linux. If appropriate, backport to the stable releases. These patches will be merged automatically in the corresponding common kernels. If the patch is already in upstream Linux, post a backport of the patch that conforms to the patch requirements below.
EXPORT_SYMBOL_GPL()
require an in-tree modular driver that uses the symbol -- so include the new driver or changes to an existing driver in the same patchset as the export.LESS GOOD: Develop your patches out-of-tree (from an upstream Linux point-of-view). Unless these are fixing an Android-specific bug, these are very unlikely to be accepted unless they have been coordinated with kernel-team@android.com. If you want to proceed, post a patch that conforms to the patch requirements below.
scripts/checkpatch.pl
UPSTREAM:
, BACKPORT:
, FROMGIT:
, FROMLIST:
, or ANDROID:
.Change-Id:
tag (see https://gerrit-review.googlesource.com/Documentation/user-changeid.html)Bug:
tag.Signed-off-by:
tag by the author and the submitterAdditional requirements are listed below based on patch type
UPSTREAM:
, BACKPORT:
UPSTREAM:
.(cherry picked from commit ...)
lineimportant patch from upstream This is the detailed description of the important patch Signed-off-by: Fred Jones <fred.jones@foo.org>
- then Joe Smith would upload the patch for the common kernel as
UPSTREAM: important patch from upstream This is the detailed description of the important patch Signed-off-by: Fred Jones <fred.jones@foo.org> Bug: 135791357 Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01 (cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1) Signed-off-by: Joe Smith <joe.smith@foo.org>
BACKPORT:
instead of UPSTREAM:
.UPSTREAM:
(cherry picked from commit ...)
lineBACKPORT: important patch from upstream This is the detailed description of the important patch Signed-off-by: Fred Jones <fred.jones@foo.org> Bug: 135791357 Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01 (cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1) [joe: Resolved minor conflict in drivers/foo/bar.c ] Signed-off-by: Joe Smith <joe.smith@foo.org>
FROMGIT:
, FROMLIST:
,FROMGIT:
(cherry picked from commit <sha1> <repo> <branch>)
. This must be a stable maintainer branch (not rebased, so don't use linux-next
for example).BACKPORT: FROMGIT:
important patch from upstream This is the detailed description of the important patch Signed-off-by: Fred Jones <fred.jones@foo.org>
- then Joe Smith would upload the patch for the common kernel as
FROMGIT: important patch from upstream This is the detailed description of the important patch Signed-off-by: Fred Jones <fred.jones@foo.org> Bug: 135791357 (cherry picked from commit 878a2fd9de10b03d11d2f622250285c7e63deace https://git.kernel.org/pub/scm/linux/kernel/git/foo/bar.git test-branch) Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01 Signed-off-by: Joe Smith <joe.smith@foo.org>
FROMLIST:
Link:
tag with a link to the submittal on lore.kernel.orgBug:
tag with the Android bug (required for patches not accepted into a maintainer tree)BACKPORT: FROMLIST:
FROMLIST: important patch from upstream This is the detailed description of the important patch Signed-off-by: Fred Jones <fred.jones@foo.org> Bug: 135791357 Link: https://lore.kernel.org/lkml/20190619171517.GA17557@someone.com/ Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01 Signed-off-by: Joe Smith <joe.smith@foo.org>
ANDROID:
ANDROID:
Fixes:
tag that cites the patch with the bugANDROID: fix android-specific bug in foobar.c This is the detailed description of the important fix Fixes: 1234abcd2468 ("foobar: add cool feature") Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01 Signed-off-by: Joe Smith <joe.smith@foo.org>
ANDROID:
Bug:
tag with the Android bug (required for android-specific features)