From 69bc8d386aebbd91a6bb44b6d33f77c8dfa9ed8c Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Fri, 26 Mar 2021 03:54:09 +0900 Subject: kbuild: generate Module.symvers only when vmlinux exists The external module build shows the following warning if Module.symvers is missing in the kernel tree. WARNING: Symbol version dump "Module.symvers" is missing. Modules may not have dependencies or modversions. I think this is an important heads-up because the resulting modules may not work as expected. This happens when you did not build the entire kernel tree, for example, you might have prepared the minimal setups for external modules by 'make defconfig && make modules_preapre'. A problem is that 'make modules' creates Module.symvers even without vmlinux. In this case, that warning is suppressed since Module.symvers already exists in spite of its incomplete content. The incomplete (i.e. invalid) Module.symvers should not be created. This commit changes the second pass of modpost to dump symbols into modules-only.symvers. The final Module.symvers is created by concatenating vmlinux.symvers and modules-only.symvers if both exist. Module.symvers is supposed to collect symbols from both vmlinux and modules. It might be a bit confusing, and I am not quite sure if it is an official interface, but presumably it is difficult to rename it because some tools (e.g. kmod) parse it. Signed-off-by: Masahiro Yamada --- scripts/mod/modpost.c | 15 +-------------- 1 file changed, 1 insertion(+), 14 deletions(-) (limited to 'scripts/mod/modpost.c') diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index 24725e50c7b4..10c3fba26f03 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -2423,19 +2423,6 @@ fail: fatal("parse error in symbol dump file\n"); } -/* For normal builds always dump all symbols. - * For external modules only dump symbols - * that are not read from kernel Module.symvers. - **/ -static int dump_sym(struct symbol *sym) -{ - if (!external_module) - return 1; - if (sym->module->from_dump) - return 0; - return 1; -} - static void write_dump(const char *fname) { struct buffer buf = { }; @@ -2446,7 +2433,7 @@ static void write_dump(const char *fname) for (n = 0; n < SYMBOL_HASH_SIZE ; n++) { symbol = symbolhash[n]; while (symbol) { - if (dump_sym(symbol)) { + if (!symbol->module->from_dump) { namespace = symbol->namespace; buf_printf(&buf, "0x%08x\t%s\t%s\t%s\t%s\n", symbol->crc, symbol->name, -- cgit From 4475dff55c54d855ef0179a055b3ce20a9c1ab3e Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Fri, 26 Mar 2021 03:54:11 +0900 Subject: kbuild: fix false-positive modpost warning when all symbols are trimmed Nathan reports that the mips defconfig emits the following warning: WARNING: modpost: Symbol info of vmlinux is missing. Unresolved symbol check will be entirely skipped. This false-positive happens when CONFIG_TRIM_UNUSED_KSYMS is enabled, but no CONFIG option is set to 'm'. Commit a0590473c5e6 ("nfs: fix PNFS_FLEXFILE_LAYOUT Kconfig default") turned the last 'm' into 'y' for the mips defconfig, and uncovered this issue. In this case, the module feature itself is enabled, but we have no module to build. As a result, CONFIG_TRIM_UNUSED_KSYMS drops all the instances of EXPORT_SYMBOL. Then, modpost wrongly assumes vmlinux is missing because vmlinux.symvers is empty. (As another false-positive case, you can create a module that does not use any symbol of vmlinux). The current behavior is to entirely suppress the unresolved symbol warnings when vmlinux is missing just because there are too many. I found the origin of this code in the historical git tree. [1] If this is a matter of noisiness, I think modpost can display the first 10 warnings, and the number of suppressed warnings at the end. You will get a bit noisier logs when you run 'make modules' without vmlinux, but such warnings are better to show because you never know the resulting modules are actually loadable or not. This commit changes the following: - If any of input *.symver files is missing, pass -w option to let the module build keep going with warnings instead of errors. - If there are too many (10+) unresolved symbol warnings, show only the first 10, and also the number of suppressed warnings. [1]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=1cc0e0529569bf6a94f6d49770aa6d4b599d2c46 Reported-by: Nathan Chancellor Signed-off-by: Masahiro Yamada --- scripts/mod/modpost.c | 25 ++++++++++++------------- 1 file changed, 12 insertions(+), 13 deletions(-) (limited to 'scripts/mod/modpost.c') diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index 10c3fba26f03..7c6bec78fa34 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -23,8 +23,6 @@ /* Are we using CONFIG_MODVERSIONS? */ static int modversions = 0; -/* Warn about undefined symbols? (do so if we have vmlinux) */ -static int have_vmlinux = 0; /* Is CONFIG_MODULE_SRCVERSION_ALL set? */ static int all_versions = 0; /* If we are modposting external module set to 1 */ @@ -41,6 +39,13 @@ static int allow_missing_ns_imports; static bool error_occurred; +/* + * Cut off the warnings when there are too many. This typically occurs when + * vmlinux is missing. ('make modules' without building vmlinux.) + */ +#define MAX_UNRESOLVED_REPORTS 10 +static unsigned int nr_unresolved; + enum export { export_plain, export_gpl, @@ -177,9 +182,6 @@ static struct module *new_module(const char *modname) mod->next = modules; modules = mod; - if (mod->is_vmlinux) - have_vmlinux = 1; - return mod; } @@ -2141,7 +2143,7 @@ static void check_exports(struct module *mod) const char *basename; exp = find_symbol(s->name); if (!exp || exp->module == mod) { - if (have_vmlinux && !s->weak) + if (!s->weak && nr_unresolved++ < MAX_UNRESOLVED_REPORTS) modpost_log(warn_unresolved ? LOG_WARN : LOG_ERROR, "\"%s\" [%s.ko] undefined!\n", s->name, mod->name); @@ -2545,13 +2547,6 @@ int main(int argc, char **argv) if (files_source) read_symbols_from_files(files_source); - /* - * When there's no vmlinux, don't print warnings about - * unresolved symbols (since there'll be too many ;) - */ - if (!have_vmlinux) - warn("Symbol info of vmlinux is missing. Unresolved symbol check will be entirely skipped.\n"); - for (mod = modules; mod; mod = mod->next) { char fname[PATH_MAX]; @@ -2595,6 +2590,10 @@ int main(int argc, char **argv) } } + if (nr_unresolved > MAX_UNRESOLVED_REPORTS) + warn("suppressed %u unresolved symbol warnings because there were too many)\n", + nr_unresolved - MAX_UNRESOLVED_REPORTS); + free(buf.p); return error_occurred ? 1 : 0; -- cgit From f3945833e436d79d9a97e776c4986af8c9cbb483 Mon Sep 17 00:00:00 2001 From: Bhaskar Chowdhury Date: Fri, 26 Mar 2021 11:22:19 +0530 Subject: scripts: modpost.c: Fix a few typos s/agorithm/algorithm/ s/criterias/criteria/ s/targetting/targeting/ ....two different places. Signed-off-by: Bhaskar Chowdhury Signed-off-by: Masahiro Yamada --- scripts/mod/modpost.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'scripts/mod/modpost.c') diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index 7c6bec78fa34..20aab6960559 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -204,7 +204,7 @@ struct symbol { static struct symbol *symbolhash[SYMBOL_HASH_SIZE]; -/* This is based on the hash agorithm from gdbm, via tdb */ +/* This is based on the hash algorithm from gdbm, via tdb */ static inline unsigned int tdb_hash(const char *name) { unsigned value; /* Used to compute the hash value. */ @@ -987,7 +987,7 @@ enum mismatch { }; /** - * Describe how to match sections on different criterias: + * Describe how to match sections on different criteria: * * @fromsec: Array of sections to be matched. * @@ -995,12 +995,12 @@ enum mismatch { * this array is forbidden (black-list). Can be empty. * * @good_tosec: Relocations applied to a section in @fromsec must be - * targetting sections in this array (white-list). Can be empty. + * targeting sections in this array (white-list). Can be empty. * * @mismatch: Type of mismatch. * * @symbol_white_list: Do not match a relocation to a symbol in this list - * even if it is targetting a section in @bad_to_sec. + * even if it is targeting a section in @bad_to_sec. * * @handler: Specific handler to call when a match is found. If NULL, * default_mismatch_handler() will be called. -- cgit From 1fdd7433a98a2f5511f49ad3f3b82bdd6f77265c Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Thu, 1 Apr 2021 16:27:23 -0700 Subject: kbuild: add an elfnote for whether vmlinux is built with lto Currently, clang LTO built vmlinux won't work with pahole. LTO introduced cross-cu dwarf tag references and broke current pahole model which handles one cu as a time. The solution is to merge all cu's as one pahole cu as in [1]. We would like to do this merging only if cross-cu dwarf references happens. The LTO build mode is a pretty good indication for that. In earlier version of this patch ([2]), clang flag -grecord-gcc-switches is proposed to add to compilation flags so pahole could detect "-flto" and then merging cu's. This will increate the binary size of 1% without LTO though. Arnaldo suggested to use a note to indicate the vmlinux is built with LTO. Such a cheap way to get whether the vmlinux is built with LTO or not helps pahole but is also useful for tracing as LTO may inline/delete/demote global functions, promote static functions, etc. So this patch added an elfnote with a new type LINUX_ELFNOTE_LTO_INFO. The owner of the note is "Linux". With gcc 8.4.1 and clang trunk, without LTO, I got $ readelf -n vmlinux Displaying notes found in: .notes Owner Data size Description ... Linux 0x00000004 func description data: 00 00 00 00 ... With "readelf -x ".notes" vmlinux", I can verify the above "func" with type code 0x101. With clang thin-LTO, I got the same as above except the following: description data: 01 00 00 00 which indicates the vmlinux is built with LTO. [1] https://lore.kernel.org/bpf/20210325065316.3121287-1-yhs@fb.com/ [2] https://lore.kernel.org/bpf/20210331001623.2778934-1-yhs@fb.com/ Suggested-by: Arnaldo Carvalho de Melo Signed-off-by: Yonghong Song Reviewed-by: Nick Desaulniers Tested-by: Sedat Dilek # LLVM/Clang v12.0.0-rc4 (x86-64) Tested-by: Arnaldo Carvalho de Melo Signed-off-by: Masahiro Yamada --- scripts/mod/modpost.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'scripts/mod/modpost.c') diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index 20aab6960559..3e623ccc020b 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -2193,10 +2193,12 @@ static void add_header(struct buffer *b, struct module *mod) */ buf_printf(b, "#define INCLUDE_VERMAGIC\n"); buf_printf(b, "#include \n"); + buf_printf(b, "#include \n"); buf_printf(b, "#include \n"); buf_printf(b, "#include \n"); buf_printf(b, "\n"); buf_printf(b, "BUILD_SALT;\n"); + buf_printf(b, "BUILD_LTO_INFO;\n"); buf_printf(b, "\n"); buf_printf(b, "MODULE_INFO(vermagic, VERMAGIC_STRING);\n"); buf_printf(b, "MODULE_INFO(name, KBUILD_MODNAME);\n"); -- cgit