user/sven/linux.git/include/linux/export.h, branch v5.14.5

export: Make CRCs robust to symbol trimming

2021-05-21T11:15:39Z

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. Acked-by: Greg Kroah-Hartman Signed-off-by: Quentin Perret Link: https://lore.kernel.org/r/20210408180105.2496212-1-qperret@google.com Signed-off-by: Greg Kroah-Hartman

module: remove EXPORT_UNUSED_SYMBOL*

2021-02-08T11:28:07Z

EXPORT_UNUSED_SYMBOL* is not actually used anywhere. Remove the unused functionality as we generally just remove unused code anyway. Reviewed-by: Miroslav Benes Reviewed-by: Emil Velikov Signed-off-by: Christoph Hellwig Signed-off-by: Jessica Yu

module: remove EXPORT_SYMBOL_GPL_FUTURE

2021-02-08T11:28:02Z

As far as I can tell this has never been used at all, and certainly not any time recently. Reviewed-by: Miroslav Benes Reviewed-by: Emil Velikov Signed-off-by: Christoph Hellwig Signed-off-by: Jessica Yu

treewide: Convert macro and uses of section(foo) to section("foo")

2020-10-25T21:51:49Z

Use a more generic form for __section that requires quotes to avoid complications with clang and gcc differences. Remove the quote operator # from compiler_attributes.h __section macro. Convert all unquoted __section(foo) uses to quoted __section("foo"). Also convert __attribute__((section("foo"))) uses to __section("foo") even if the __attribute__ has multiple list entry forms. Conversion done using the script at: https://lore.kernel.org/lkml/75393e5ddc272dc7403de74d645e6c6e0f4e70eb.camel@perches.com/2-convert_section.pl Signed-off-by: Joe Perches Reviewed-by: Nick Desaulniers Reviewed-by: Miguel Ojeda Signed-off-by: Linus Torvalds

export.h: fix section name for CONFIG_TRIM_UNUSED_KSYMS for Clang

2020-10-14T01:38:26Z

When enabling CONFIG_TRIM_UNUSED_KSYMS, the linker will warn about the orphan sections: (".discard.ksym") is being placed in '".discard.ksym"' repeatedly when linking vmlinux. This is because the stringification operator, `#`, in the preprocessor escapes strings. GCC and Clang differ in how they treat section names that contain \". The portable solution is to not use a string literal with the preprocessor stringification operator. Fixes: commit bbda5ec671d3 ("kbuild: simplify dependency generation for CONFIG_TRIM_UNUSED_KSYMS") Reported-by: kbuild test robot Suggested-by: Kees Cook Signed-off-by: Nick Desaulniers Signed-off-by: Andrew Morton Reviewed-by: Kees Cook Cc: Nathan Chancellor Cc: Masahiro Yamada Cc: Matthias Maennich Cc: Jessica Yu Cc: Greg Kroah-Hartman Cc: Will Deacon Link: https://bugs.llvm.org/show_bug.cgi?id=42950 Link: https://github.com/ClangBuiltLinux/linux/issues/1166 Link: https://lkml.kernel.org/r/20200929190701.398762-1-ndesaulniers@google.com Signed-off-by: Linus Torvalds

export.h: reduce __ksymtab_strings string duplication by using "MS" section flags

2019-12-16T09:35:33Z

Commit c3a6cf19e695 ("export: avoid code duplication in include/linux/export.h") refactors export.h quite nicely, but introduces a slight increase in memory usage due to using the empty string "" instead of NULL to indicate that an exported symbol has no namespace. As mentioned in that commit, this meant an increase of 1 byte per exported symbol without a namespace. For example, if a kernel configuration has about 10k exported symbols, this would mean that the size of __ksymtab_strings would increase by roughly 10kB. We can alleviate this situation by utilizing the SHF_MERGE and SHF_STRING section flags. SHF_MERGE|SHF_STRING indicate to the linker that the data in the section are null-terminated strings that can be merged to eliminate duplication. More specifically, from the binutils documentation - "for sections with both M and S, a string which is a suffix of a larger string is considered a duplicate. Thus "def" will be merged with "abcdef"; A reference to the first "def" will be changed to a reference to "abcdef"+3". Thus, all the empty strings would be merged as well as any strings that can be merged according to the cited method above. For example, "memset" and "__memset" would be merged to just "__memset" in __ksymtab_strings. As of v5.4-rc5, the following statistics were gathered with x86 defconfig with approximately 10.7k exported symbols. Size of __ksymtab_strings in vmlinux: ------------------------------------- v5.4-rc5: 213834 bytes v5.4-rc5 with commit c3a6cf19e695: 224455 bytes v5.4-rc5 with this patch: 205759 bytes So, we already see memory savings of ~8kB compared to vanilla -rc5 and savings of nearly 18.7kB compared to -rc5 with commit c3a6cf19e695 on top. Unfortunately, as of this writing, strings will not get deduplicated for kernel modules, as ld does not do the deduplication for SHF_MERGE|SHF_STRINGS sections for relocatable files (ld -r), which kernel modules are. A patch for ld is currently being worked on to hopefully allow for string deduplication in relocatable files in the future. Suggested-by: Rasmus Villemoes Reviewed-by: Masahiro Yamada Reviewed-by: Matthias Maennich Signed-off-by: Jessica Yu

Merge tag 'modules-for-v5.5' of git://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux

2019-12-05T20:27:16Z

Pull modules updates from Jessica Yu: "Summary of modules changes for the 5.5 merge window: - Refactor include/linux/export.h and remove code duplication between EXPORT_SYMBOL and EXPORT_SYMBOL_NS to make it more readable. The most notable change is that no namespace is represented by an empty string "" rather than NULL. - Fix a module load/unload race where waiter(s) trying to load the same module weren't being woken up when a module finally goes away" * tag 'modules-for-v5.5' of git://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux: kernel/module.c: wakeup processes in module_wq on module unload moduleparam: fix parameter description mismatch export: avoid code duplication in include/linux/export.h

export,module: add SPDX GPL-2.0 license identifier to headers with no license

2019-11-14T03:36:53Z

Commit b24413180f56 ("License cleanup: add SPDX GPL-2.0 license identifier to files with no license") took care of a lot of files without any license information. These headers were not processed by the tool perhaps because they contain "GPL" in the code. I do not see any license boilerplate in them, so they fall back to GPL version 2 only, which is the project default. Signed-off-by: Masahiro Yamada Link: https://lore.kernel.org/r/20191018045053.8424-1-yamada.masahiro@socionext.com Signed-off-by: Greg Kroah-Hartman

export: avoid code duplication in include/linux/export.h

2019-10-28T15:38:26Z

include/linux/export.h has lots of code duplication between EXPORT_SYMBOL and EXPORT_SYMBOL_NS. To improve the maintainability and readability, unify the implementation. When the symbol has no namespace, pass the empty string "" to the 'ns' parameter. The drawback of this change is, it grows the code size. When the symbol has no namespace, sym->namespace was previously NULL, but it is now an empty string "". So, it increases 1 byte for every no namespace EXPORT_SYMBOL. A typical kernel configuration has 10K exported symbols, so it increases 10KB in rough estimation. I did not come up with a good idea to refactor it without increasing the code size. I am not sure how big a deal it is, but at least include/linux/export.h looks nicer. Reviewed-by: Greg Kroah-Hartman Signed-off-by: Masahiro Yamada [maennich: rebase on top of 3 fixes for the namespace feature] Signed-off-by: Matthias Maennich Signed-off-by: Jessica Yu

symbol namespaces: revert to previous __ksymtab name scheme

2019-10-18T13:32:52Z

The introduction of Symbol Namespaces changed the naming schema of the __ksymtab entries from __kysmtab__symbol to __ksymtab_NAMESPACE.symbol. That caused some breakages in tools that depend on the name layout in either the binaries(vmlinux,*.ko) or in System.map. E.g. kmod's depmod would not be able to read System.map without a patch to support symbol namespaces. A warning reported by depmod for namespaced symbols would look like depmod: WARNING: [...]/uas.ko needs unknown symbol usb_stor_adjust_quirks In order to address this issue, revert to the original naming scheme and rather read the __kstrtabns_ entries and their corresponding values from __ksymtab_strings to update the namespace values for symbols. After having read all symbols and handled them in handle_modversions(), the symbols are created. In a second pass, read the __kstrtabns_ entries and update the namespaces accordingly. Fixes: 8651ec01daed ("module: add support for symbol namespaces.") Reported-by: Stefan Wahren Suggested-by: Masahiro Yamada Acked-by: Will Deacon Reviewed-by: Greg Kroah-Hartman Reviewed-by: Masahiro Yamada Signed-off-by: Matthias Maennich Signed-off-by: Jessica Yu