On Thu, 12 Mar 2026 18:20:10 +0000 Vincent Donnefort <[email protected]> wrote:
> Compiler and tooling-generated symbols are difficult to maintain > across all supported architectures. Make the allowlist more robust by > replacing the harcoded list with a mechanism that automatically detects > these symbols. > > This mechanism generates a C function designed to trigger common > compiler-inserted symbols. > > Signed-off-by: Vincent Donnefort <[email protected]> > > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile > index beb15936829d..3b427b76434a 100644 > --- a/kernel/trace/Makefile > +++ b/kernel/trace/Makefile > @@ -136,17 +136,37 @@ obj-$(CONFIG_TRACE_REMOTE_TEST) += remote_test.o > # simple_ring_buffer is used by the pKVM hypervisor which does not have > access > # to all kernel symbols. Fail the build if forbidden symbols are found. > # > -UNDEFINED_ALLOWLIST := memset alt_cb_patch_nops __x86 __ubsan __asan __kasan > __gcov __aeabi_unwind > -UNDEFINED_ALLOWLIST += __stack_chk_fail stackleak_track_stack __ref_stack > __sanitizer llvm_gcda llvm_gcov > -UNDEFINED_ALLOWLIST += .TOC\. __clear_pages_unrolled __memmove copy_page > warn_slowpath_fmt > -UNDEFINED_ALLOWLIST += ftrace_likely_update __hwasan_load __hwasan_store > __hwasan_tag_memory > -UNDEFINED_ALLOWLIST += warn_bogus_irq_restore __stack_chk_guard > -UNDEFINED_ALLOWLIST := $(addprefix -e , $(UNDEFINED_ALLOWLIST)) > +# undefsyms_base generates a set of compiler and tooling-generated symbols > that can > +# safely be ignored for simple_ring_buffer. > +# > +$(obj)/undefsyms_base.c: FORCE > + $(Q)echo '#include <asm/page.h>' > $@ > + $(Q)echo '#include <asm/local.h>' >> $@ > + $(Q)echo 'static char page[PAGE_SIZE] __aligned(PAGE_SIZE);' >> $@ > + $(Q)echo 'void undefsyms_base(int n);' >> $@ > + $(Q)echo 'void undefsyms_base(int n) {' >> $@ > + $(Q)echo ' char buffer[256] = { 0 };' >> $@ > + $(Q)echo ' u32 u = 0;' >> $@ > + $(Q)echo ' memset((char * volatile)page, 8, PAGE_SIZE);' >> $@ > + $(Q)echo ' memset((char * volatile)buffer, 8, sizeof(buffer));' >> > $@ > + $(Q)echo ' cmpxchg((u32 * volatile)&u, 0, 8);' >> $@ > + $(Q)echo ' WARN_ON(n == 0xdeadbeef);' >> $@ > + $(Q)echo '}' >> $@ Looking at the scripts/Makefile.* files, it looks like the proper way to do C files is to make it a single command: Perhaps something like: $(obj)/undefsyms_base.c: FORCE $(Q)( \ echo '#include <asm/page.h>'; \ echo '#include <asm/local.h>'; \ echo 'static char page[PAGE_SIZE] __aligned(PAGE_SIZE);'; \ echo 'void undefsyms_base(int n);'; \ echo 'void undefsyms_base(int n) {'; \ echo ' char buffer[256] = { 0 };'; \ echo ' u32 u = 0;'; \ echo ' memset((char * volatile)page, 8, PAGE_SIZE);'; \ echo ' memset((char * volatile)buffer, 8, sizeof(buffer));'; \ echo ' cmpxchg((u32 * volatile)&u, 0, 8);'; \ echo ' WARN_ON(n == 0xdeadbeef);'; \ echo '}' ) > $@ -- Steve > + > +clean-files += undefsyms_base.c > +targets += undefsyms_base.c > + > +$(obj)/undefsyms_base.o: $(obj)/undefsyms_base.c > + > +extra-y += undefsyms_base.o > + > +UNDEFINED_ALLOWLIST = __asan __gcov __kasan __kcsan __hwasan __sanitizer > __tsan __ubsan __x86_indirect_thunk \ > + $(shell $(NM) -u $(obj)/undefsyms_base.o 2>/dev/null | > awk '{print $$2}') > > quiet_cmd_check_undefined = NM $< > - cmd_check_undefined = test -z "`$(NM) -u $< | grep -v > $(UNDEFINED_ALLOWLIST)`" > + cmd_check_undefined = test -z "`$(NM) -u $< | grep -v $(addprefix -e > ,$(UNDEFINED_ALLOWLIST))`" > > -$(obj)/%.o.checked: $(obj)/%.o FORCE > +$(obj)/%.o.checked: $(obj)/%.o $(obj)/undefsyms_base.o FORCE > $(call if_changed,check_undefined) > > always-$(CONFIG_SIMPLE_RING_BUFFER) += simple_ring_buffer.o.checked > > base-commit: 33f2e266515717c4b2df585dadefa0525557726c
