| Message ID | 20191018093143.15997-1-maennich@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
+++ Matthias Maennich [18/10/19 10:31 +0100]: >The introduction of the symbol namespace patches changed the way symbols are >named in the ksymtab entries. That caused userland tools to fail (such as >kmod's depmod). As depmod is used as part of the kernel build it was worth >having another look whether this name change can be avoided. > >The main purpose of this series is to restore the original ksymtab entry names. >For that to happen and to remove some rough edges around that, the relevant >parts in modpost got a small refactoring as to when and how namespaces are >evaluated and set in the symbol struct. > >Eventually, the namespace values can be read from __kstrtabns_ entries and >their corresponding __ksymtab_strings values. That removes the need to carry >the namespace names within the (anyway unique) symbol name entries. > >The last patch of this series is adopted from Masahiro [1]. By allowing 'no >namespace' to be represented as empty string, large chunks of >include/linux/export.h could be consolidated. Technically, this last patch is >not absolutely necessary to fix functionality. It addresses concerns about >maintainability and readability. While I strongly suggest sending all of the >patches for 5.4, the last one could possible deferred to the next merge window. > >This patch applies to the modules-linus [2] branch. Hi! I've applied the first three patches to modules-linus, inbound for -rc5. Patch 4/4 was agreed to be for 5.5, and will be applied to modules-next once I rebase that branch against -rc5. Thanks! Jessica >Changes since v2: > - restored correct authorship for [4/4] > - add missing contributor tags > - fixed typos and code style (spaces/tabs) > >[1] https://lore.kernel.org/lkml/20190927093603.9140-5-yamada.masahiro@socionext.com/ >[2] https://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux.git/log/?h=modules-linus > >Cc: Jessica Yu <jeyu@kernel.org> >Cc: Masahiro Yamada <yamada.masahiro@socionext.com> >Cc: Martijn Coenen <maco@android.com> >Cc: Lucas De Marchi <lucas.de.marchi@gmail.com> >Cc: Shaun Ruffell <sruffell@sruffell.net> >Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> >Cc: Will Deacon <will@kernel.org> >Cc: linux-kbuild@vger.kernel.org >Cc: linux-modules@vger.kernel.org > > >Masahiro Yamada (1): > export: avoid code duplication in include/linux/export.h > >Matthias Maennich (3): > modpost: delegate updating namespaces to separate function > modpost: make updating the symbol namespace explicit > symbol namespaces: revert to previous __ksymtab name scheme > > include/linux/export.h | 97 +++++++++++++----------------------------- > kernel/module.c | 2 +- > scripts/mod/modpost.c | 59 ++++++++++++++++--------- > scripts/mod/modpost.h | 1 + > 4 files changed, 71 insertions(+), 88 deletions(-) > >Interdiff against v1: >diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c >index 7cf0065ac95f..0bf7eab80d9f 100644 >--- a/scripts/mod/modpost.c >+++ b/scripts/mod/modpost.c >@@ -357,18 +357,21 @@ static const char *namespace_from_kstrtabns(struct elf_info *info, > > static void sym_update_namespace(const char *symname, const char *namespace) > { >- struct symbol *s = find_symbol(symname); >- /* That symbol should have been created earlier and thus this is >- * actually an assertion. */ >- if (!s) { >- merror("Could not update namespace(%s) for symbol %s\n", >- namespace, symname); >- return; >- } >- >- free(s->namespace); >- s->namespace = >- namespace && namespace[0] ? NOFAIL(strdup(namespace)) : NULL; >+ struct symbol *s = find_symbol(symname); >+ >+ /* >+ * That symbol should have been created earlier and thus this is >+ * actually an assertion. >+ */ >+ if (!s) { >+ merror("Could not update namespace(%s) for symbol %s\n", >+ namespace, symname); >+ return; >+ } >+ >+ free(s->namespace); >+ s->namespace = >+ namespace && namespace[0] ? NOFAIL(strdup(namespace)) : NULL; > } > > /** >-- >2.23.0.866.gb869b98d4c-goog >
On Fri, Oct 18, 2019 at 10:31:39AM +0100, Matthias Maennich wrote: > The introduction of the symbol namespace patches changed the way symbols are > named in the ksymtab entries. That caused userland tools to fail (such as > kmod's depmod). As depmod is used as part of the kernel build it was worth > having another look whether this name change can be avoided. Why have this as a default feature? What about having an option to disable this feature? The benefit being that without a full swing of tests to avoid regressions its not clear what other issues may creep up. With this as optional, those wanting the mechanism can enable it and happilly find the issues for those more conservative. Luis
On Wed, Oct 23, 2019 at 12:22:22PM +0000, Luis Chamberlain wrote: >On Fri, Oct 18, 2019 at 10:31:39AM +0100, Matthias Maennich wrote: >> The introduction of the symbol namespace patches changed the way symbols are >> named in the ksymtab entries. That caused userland tools to fail (such as >> kmod's depmod). As depmod is used as part of the kernel build it was worth >> having another look whether this name change can be avoided. > >Why have this as a default feature? What about having an option to >disable this feature? The benefit being that without a full swing of >tests to avoid regressions its not clear what other issues may creep >up. With this as optional, those wanting the mechanism can enable it >and happilly find the issues for those more conservative. The strongest argument against that is, that the 'conservative' people would constantly break things for the more 'adventurous' ones. They would introduce namespace requirements by just using symbols without correctly adjusting the imports. Second, vmlinux and modules would have to be compiled in the same configuration. Otherwise they are incompatible and we would likely have to maintain code in the module loader to catch issues caused by that. In general, I think for the adoption of this feature and one of its purposes - making unexpected use of symbols across the tree visible already at review time - we should not make this an optional one. Enforcing the imports at module load time is optional (there is an option). And finally, having that code configurable for both options introduces quite some complexity in kernel/module.c, modpost and include/linux/export.h that would make the code hard to maintain and complex to test. Hence that would likely introduce more issues. I know the feature came with some rough edges. Sorry about that. I think, we got most of them worked out pretty well (big thanks to Masahiro and Jessica and others helping with that). Now the actual change to the surface exposed to userland tools is much smaller and the feature itself less intrusive. Cheers, Matthias > > Luis
On Thu, Oct 24, 2019 at 10:35:46AM +0100, Matthias Maennich wrote: > On Wed, Oct 23, 2019 at 12:22:22PM +0000, Luis Chamberlain wrote: > > On Fri, Oct 18, 2019 at 10:31:39AM +0100, Matthias Maennich wrote: > > > The introduction of the symbol namespace patches changed the way symbols are > > > named in the ksymtab entries. That caused userland tools to fail (such as > > > kmod's depmod). As depmod is used as part of the kernel build it was worth > > > having another look whether this name change can be avoided. > > > > Why have this as a default feature? What about having an option to > > disable this feature? The benefit being that without a full swing of > > tests to avoid regressions its not clear what other issues may creep > > up. With this as optional, those wanting the mechanism can enable it > > and happilly find the issues for those more conservative. > > The strongest argument against that is, that the 'conservative' people > would constantly break things for the more 'adventurous' ones. They > would introduce namespace requirements by just using symbols without > correctly adjusting the imports. > > Second, vmlinux and modules would have to be compiled in the same > configuration. Otherwise they are incompatible and we would likely have > to maintain code in the module loader to catch issues caused by that. > In general, I think for the adoption of this feature and one of its > purposes - making unexpected use of symbols across the tree visible > already at review time - we should not make this an optional one. > Enforcing the imports at module load time is optional (there is an > option). > > And finally, having that code configurable for both options introduces > quite some complexity in kernel/module.c, modpost and > include/linux/export.h that would make the code hard to maintain and > complex to test. Hence that would likely introduce more issues. > > I know the feature came with some rough edges. Sorry about that. I > think, we got most of them worked out pretty well (big thanks to > Masahiro and Jessica and others helping with that). Now the actual > change to the surface exposed to userland tools is much smaller and the > feature itself less intrusive. This logic makes sense, the complexity over module loading is already high and supporting yet another division would be a burden for review and maintenace. However I'd feel much more inclined to support such decisions when and if we had a series of test cases to prevent possible regressions. Since effort with testing will move forward, I'm happy with the status quo. Luis
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index 7cf0065ac95f..0bf7eab80d9f 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -357,18 +357,21 @@ static const char *namespace_from_kstrtabns(struct elf_info *info, static void sym_update_namespace(const char *symname, const char *namespace) { - struct symbol *s = find_symbol(symname); - /* That symbol should have been created earlier and thus this is - * actually an assertion. */ - if (!s) { - merror("Could not update namespace(%s) for symbol %s\n", - namespace, symname); - return; - } - - free(s->namespace); - s->namespace = - namespace && namespace[0] ? NOFAIL(strdup(namespace)) : NULL; + struct symbol *s = find_symbol(symname); + + /* + * That symbol should have been created earlier and thus this is + * actually an assertion. + */ + if (!s) { + merror("Could not update namespace(%s) for symbol %s\n", + namespace, symname); + return; + } + + free(s->namespace); + s->namespace = + namespace && namespace[0] ? NOFAIL(strdup(namespace)) : NULL; } /**