https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98997
Bug ID: 98997 Summary: Linking mismatched -fcf-protection objects generates incorrect code Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: luto at kernel dot org Target Milestone: --- $ gcc --version gcc (GCC) 10.2.1 20201125 (Red Hat 10.2.1-9) Copyright (C) 2020 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. $ cat cet1.c #include <setjmp.h> void test(jmp_buf buf) { __builtin_longjmp(buf, 1); } $ cat cet2.c #include <setjmp.h> void test(jmp_buf buf); int main() { jmp_buf buf; if (__builtin_setjmp(buf) == 0) test(buf); return 0; } $ gcc -c -O2 cet1.c -fcf-protection=full $ gcc -c -O2 cet2.c $ gcc -o cet -O2 cet1.o cet2.o $ ./cet Illegal instruction (core dumped) Presumably the magic CET fixup in the builtin setjmp/longjmp requires that matching code is generated for both. I'm testing on a non-CET system. I haven't even tried to figure out if anything sensible happens to the CET GNU property, but I think the current GCC behavior is impolite at best. I think GCC should do one of a few things: 1. Generate working code. 2. Fail to link. 3. At least document this pitfall very clearly. I really hope this doesn't affect shared objects.