tracing: Generate undef symbols allowlist for simple_ring_buffer

# 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.

#

filechk_undefsyms_base = \

	echo '$(pound)include <linux/atomic.h>'; \

	echo '$(pound)include <linux/string.h>'; \

	echo '$(pound)include <asm/page.h>'; \

	echo 'static char page[PAGE_SIZE] __aligned(PAGE_SIZE);'; \

	echo 'void undefsyms_base(void *p, int n);'; \

	echo 'void undefsyms_base(void *p, 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 '	memcpy((void * volatile)p, buffer, sizeof(buffer));'; \

	echo '	cmpxchg((u32 * volatile)&u, 0, 8);'; \

	echo '	WARN_ON(n == 0xdeadbeef);'; \

	echo '}'

$(obj)/undefsyms_base.c: FORCE

	$(call filechk,undefsyms_base)

clean-files += undefsyms_base.c

$(obj)/undefsyms_base.o: $(obj)/undefsyms_base.c

targets += undefsyms_base.o

# Ensure KASAN is enabled to avoid logic that may disable FORTIFY_SOURCE when

# KASAN is not enabled. undefsyms_base.o does not automatically get KASAN flags

# because it is not linked into vmlinux.

KASAN_SANITIZE_undefsyms_base.o := y

UNDEFINED_ALLOWLIST = __asan __gcov __kasan __kcsan __hwasan __sancov __sanitizer __tsan __ubsan __x86_indirect_thunk \

		      __msan simple_ring_buffer \

		      $(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