On Fri, Oct 27, 2023 at 1:30 PM Greg Ungerer <gregungerer@xxxxxxxxxxxxxx> wrote: > > Hi Masahiro, > > On 15/5/23 01:27, Masahiro Yamada wrote: > > Commit 7b4537199a4a ("kbuild: link symbol CRCs at final link, removing > > CONFIG_MODULE_REL_CRCS") made modpost output CRCs in the same way > > whether the EXPORT_SYMBOL() is placed in *.c or *.S. > > > > This commit applies a similar approach to the entire data structure of > > EXPORT_SYMBOL() for further cleanups. The EXPORT_SYMBOL() compilation > > is split into two stages. > > > > When a source file is compiled, EXPORT_SYMBOL() is converted into a > > dummy symbol in the .export_symbol section. > > > > For example, > > > > EXPORT_SYMBOL(foo); > > EXPORT_SYMBOL_NS_GPL(bar, BAR_NAMESPACE); > > > > will be encoded into the following assembly code: > > > > .section ".export_symbol","a" > > __export_symbol__foo: > > .asciz "" > > .balign 8 > > .quad foo > > .previous > > > > .section ".export_symbol","a" > > __export_symbol_gpl_bar: > > .asciz "BAR_NAMESPACE" > > .balign 8 > > .quad bar > > .previous > > > > They are just markers to tell modpost the name, license, and namespace > > of the symbols. They will be dropped from the final vmlinux and modules > > because the *(.export_symbol) will go into /DISCARD/ in the linker script. > > > > Then, modpost extracts all the information about EXPORT_SYMBOL() from the > > .export_symbol section, and generates C code: > > > > KSYMTAB_FUNC(foo, "", ""); > > KSYMTAB_FUNC(bar, "_gpl", "BAR_NAMESPACE"); > > > > KSYMTAB_FUNC() (or KSYMTAB_DATA() if it is data) is expanded to struct > > kernel_symbol that will be linked to the vmlinux or a module. > > > > With this change, EXPORT_SYMBOL() works in the same way for *.c and *.S > > files, providing the following benefits. > > > > [1] Deprecate EXPORT_DATA_SYMBOL() > > > > In the old days, EXPORT_SYMBOL() was only available in C files. To export > > a symbol in *.S, EXPORT_SYMBOL() was placed in a separate *.c file. > > arch/arm/kernel/armksyms.c is one example written in the classic manner. > > > > Commit 22823ab419d8 ("EXPORT_SYMBOL() for asm") removed this limitation. > > Since then, EXPORT_SYMBOL() can be placed close to the symbol definition > > in *.S files. It was a nice improvement. > > > > However, as that commit mentioned, you need to use EXPORT_DATA_SYMBOL() > > for data objects on some architectures. > > > > In the new approach, modpost checks symbol's type (STT_FUNC or not), > > and outputs KSYMTAB_FUNC() or KSYMTAB_DATA() accordingly. > > > > There are only two users of EXPORT_DATA_SYMBOL: > > > > EXPORT_DATA_SYMBOL_GPL(empty_zero_page) (arch/ia64/kernel/head.S) > > EXPORT_DATA_SYMBOL(ia64_ivt) (arch/ia64/kernel/ivt.S) > > > > They are transformed as follows and output into .vmlinux.export.c > > > > KSYMTAB_DATA(empty_zero_page, "_gpl", ""); > > KSYMTAB_DATA(ia64_ivt, "", ""); > > > > The other EXPORT_SYMBOL users in ia64 assembly are output as > > KSYMTAB_FUNC(). > > > > EXPORT_DATA_SYMBOL() is now deprecated. > > > > [2] merge <linux/export.h> and <asm-generic/export.h> > > > > There are two similar header implementations: > > > > include/linux/export.h for .c files > > include/asm-generic/export.h for .S files > > > > Ideally, the functionality should be consistent between them, but they > > tend to diverge. > > > > Commit 8651ec01daed ("module: add support for symbol namespaces.") did > > not support the namespace for *.S files. > > > > This commit shifts the essential implementation part to C, which supports > > EXPORT_SYMBOL_NS() for *.S files. > > > > <asm/export.h> and <asm-generic/export.h> will remain as a wrapper of > > <linux/export.h> for a while. > > > > They will be removed after #include <asm/export.h> directives are all > > replaced with #include <linux/export.h>. > > > > [3] Implement CONFIG_TRIM_UNUSED_KSYMS in one-pass algorithm (by a later commit) > > > > When CONFIG_TRIM_UNUSED_KSYMS is enabled, Kbuild recursively traverses > > the directory tree to determine which EXPORT_SYMBOL to trim. If an > > EXPORT_SYMBOL turns out to be unused by anyone, Kbuild begins the > > second traverse, where some source files are recompiled with their > > EXPORT_SYMBOL() tuned into a no-op. > > > > We can do this better now; modpost can selectively emit KSYMTAB entries > > that are really used by modules. > > > > Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> > > This breaks building kernels with an m68k-uclinux-gcc toolchain that have > modules configured. Before this change they built and ran fine. > They build and run fine if CONFIG_MODULES is not set. > > A few hundred errors like this spew out: > > scripts/mod/modpost -o Module.symvers -T modules.order vmlinux.o > ERROR: modpost: vmlinux: .export_symbol section references '', but it does not seem to be an export symbol > ERROR: modpost: vmlinux: .export_symbol section references '', but it does not seem to be an export symbol > ERROR: modpost: vmlinux: .export_symbol section references '', but it does not seem to be an export symbol > ... Where can I download a prebuilt m68k-uclinux-gcc? -- Best Regards Masahiro Yamada