Messages in this thread Patch in this message | | | Date | Fri, 15 Jan 2021 09:14:42 +0100 | From | Jessica Yu <> | Subject | Re: [PATCH v2] module: Ignore _GLOBAL_OFFSET_TABLE_ when warning for undefined symbols |
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+++ Marco Elver [15/01/21 08:03 +0100]: >On Thu, 14 Jan 2021 at 22:54, Fangrui Song <maskray@google.com> wrote: >> clang-12 -fno-pic (since >> https://github.com/llvm/llvm-project/commit/a084c0388e2a59b9556f2de0083333232da3f1d6) >> can emit `call __stack_chk_fail@PLT` instead of `call __stack_chk_fail` >> on x86. The two forms should have identical behaviors on x86-64 but the >> former causes GNU as<2.37 to produce an unreferenced undefined symbol >> _GLOBAL_OFFSET_TABLE_. >> >> (On x86-32, there is an R_386_PC32 vs R_386_PLT32 difference but the >> linker behavior is identical as far as Linux kernel is concerned.) >> >> Simply ignore _GLOBAL_OFFSET_TABLE_ for now, like what >> scripts/mod/modpost.c:ignore_undef_symbol does. This also fixes the >> problem for gcc/clang -fpie and -fpic, which may emit `call foo@PLT` for >> external function calls on x86. >> >> Note: ld -z defs and dynamic loaders do not error for unreferenced >> undefined symbols so the module loader is reading too much. If we ever >> need to ignore more symbols, the code should be refactored to ignore >> unreferenced symbols. >> >> Reported-by: Marco Elver <elver@google.com> >> Link: https://github.com/ClangBuiltLinux/linux/issues/1250 >> Signed-off-by: Fangrui Song <maskray@google.com> > >Tested-by: Marco Elver <elver@google.com> > >Thank you for the patch! > >> --- >> kernel/module.c | 20 ++++++++++++++++++-- >> 1 file changed, 18 insertions(+), 2 deletions(-) >> --- >> Changes in v2: >> * Fix Marco's email address >> * Add a function ignore_undef_symbol similar to scripts/mod/modpost.c:ignore_undef_symbol >> >> diff --git a/kernel/module.c b/kernel/module.c >> index 4bf30e4b3eaa..278f5129bde2 100644 >> --- a/kernel/module.c >> +++ b/kernel/module.c >> @@ -2348,6 +2348,20 @@ static int verify_exported_symbols(struct module *mod) >> return 0; >> } >> >> +static int ignore_undef_symbol(Elf_Half emachine, const char *name) > >Why not 'bool' return-type? > >> +{ >> + /* On x86, PIC code and Clang non-PIC code may have call foo@PLT. GNU as > >Not sure if checkpatch.pl warns about this, but this multi-line >comment does not follow the normal kernel-style (see elsewhere in >file): > >/* > * ... > */
+1 to Marco's comments. Otherwise, patch looks good to me.
Thanks Fangrui!
Jessica
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