* [PATCH] tracing: Generate undef symbols allowlist for simple_ring_buffer @ 2026-03-12 18:20 Vincent Donnefort 2026-03-12 18:43 ` Steven Rostedt 2026-03-12 23:51 ` Nathan Chancellor 0 siblings, 2 replies; 4+ messages in thread From: Vincent Donnefort @ 2026-03-12 18:20 UTC (permalink / raw) To: maz Cc: rostedt, arnd, nathan, linux-trace-kernel, kvmarm, kernel-team, Vincent Donnefort 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 <vdonnefort@google.com> 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 '}' >> $@ + +clean-files += undefsyms_base.c +targets += undefsyms_base.c + +$(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 -- 2.53.0.851.ga537e3e6e9-goog ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] tracing: Generate undef symbols allowlist for simple_ring_buffer 2026-03-12 18:20 [PATCH] tracing: Generate undef symbols allowlist for simple_ring_buffer Vincent Donnefort @ 2026-03-12 18:43 ` Steven Rostedt 2026-03-12 23:51 ` Nathan Chancellor 1 sibling, 0 replies; 4+ messages in thread From: Steven Rostedt @ 2026-03-12 18:43 UTC (permalink / raw) To: Vincent Donnefort Cc: maz, arnd, nathan, linux-trace-kernel, kvmarm, kernel-team On Thu, 12 Mar 2026 18:20:10 +0000 Vincent Donnefort <vdonnefort@google.com> 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 <vdonnefort@google.com> > > 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 ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] tracing: Generate undef symbols allowlist for simple_ring_buffer 2026-03-12 18:20 [PATCH] tracing: Generate undef symbols allowlist for simple_ring_buffer Vincent Donnefort 2026-03-12 18:43 ` Steven Rostedt @ 2026-03-12 23:51 ` Nathan Chancellor 2026-03-13 10:23 ` Vincent Donnefort 1 sibling, 1 reply; 4+ messages in thread From: Nathan Chancellor @ 2026-03-12 23:51 UTC (permalink / raw) To: Vincent Donnefort Cc: maz, rostedt, arnd, linux-trace-kernel, kvmarm, kernel-team Hi Vincent, On Thu, Mar 12, 2026 at 06:20:10PM +0000, Vincent Donnefort 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. This certainly seems more robust. > Signed-off-by: Vincent Donnefort <vdonnefort@google.com> > > 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 '}' >> $@ This should use filechk, otherwise undefsyms_base.c will be regenerated every build, resulting in undefsyms_base.o being rebuilt every time. $ make -skj"$(nproc)" ARCH=x86_64 mrproper allmodconfig kernel/trace/ $ make -skj"$(nproc)" ARCH=x86_64 V=2 kernel/trace/ ... CC kernel/trace/undefsyms_base.o - due to: kernel/trace/undefsyms_base.c NM kernel/trace/simple_ring_buffer.o - due to target missing filechk_undefsyms_base = { \ echo '$(pound)include <asm/page.h>'; \ echo '$(pound)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 '}'; \ } $(obj)/undefsyms_base.c: FORCE $(call filechk,undefsyms_base) $ make -skj"$(nproc)" ARCH=x86_64 mrproper allmodconfig kernel/trace/ $ make -skj"$(nproc)" ARCH=x86_64 V=2 kernel/trace/ GEN Makefile - due to target is PHONY DESCEND objtool CALL scripts/checksyscalls.sh - due to target is PHONY INSTALL libsubcmd_headers NM kernel/trace/simple_ring_buffer.o - due to target missing > +clean-files += undefsyms_base.c > +targets += undefsyms_base.c I don't think this targets addition is necessary. > +$(obj)/undefsyms_base.o: $(obj)/undefsyms_base.c > + > +extra-y += undefsyms_base.o I think this should be targets += undefsyms_base.o as extra-y is deprecated per Documentation/kbuild/makefiles.rst. > +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}') With an allmodconfig + ThinLTO build, I still see: $ cat allmod.config CONFIG_GCOV_KERNEL=n CONFIG_KASAN=n CONFIG_LTO_CLANG_THIN=y $ make -skj"$(nproc)" ARCH=x86_64 KCONFIG_ALLCONFIG=1 LLVM=1 mrproper allmodconfig kernel/trace/ Unexpected symbols in kernel/trace/simple_ring_buffer.o: U __fortify_panic U __write_overflow_field U simple_ring_buffer_commit U simple_ring_buffer_enable_tracing U simple_ring_buffer_init U simple_ring_buffer_reserve U simple_ring_buffer_reset U simple_ring_buffer_swap_reader_page U simple_ring_buffer_unload Something like: diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index 48c415a0c7e4..0f9a6ce9abd9 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -142,13 +142,15 @@ obj-$(CONFIG_TRACE_REMOTE_TEST) += remote_test.o filechk_undefsyms_base = { \ echo '$(pound)include <asm/page.h>'; \ echo '$(pound)include <asm/local.h>'; \ + echo '$(pound)include <linux/string.h>'; \ echo 'static char page[PAGE_SIZE] __aligned(PAGE_SIZE);'; \ - echo 'void undefsyms_base(int n);'; \ - echo 'void undefsyms_base(int n) {'; \ + echo 'void undefsyms_base(int n, void *ptr);'; \ + echo 'void undefsyms_base(int n, void *ptr) {'; \ 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)ptr, buffer, sizeof(buffer));'; \ echo ' cmpxchg((u32 * volatile)&u, 0, 8);'; \ echo ' WARN_ON(n == 0xdeadbeef);'; \ echo '}'; \ -- cures the first two. The simple_ring_buffer symbols are very odd... $ llvm-nm kernel/trace/simple_ring_buffer.o | grep simple_ring_buffer ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_commit_845 ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_enable_tracing_849 ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_init_847 ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_reserve_841 ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_reset_846 ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_swap_reader_page_837 ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_unload_848 ---------------- t __export_symbol_simple_ring_buffer_commit ---------------- t __export_symbol_simple_ring_buffer_enable_tracing ---------------- t __export_symbol_simple_ring_buffer_init ---------------- t __export_symbol_simple_ring_buffer_reserve ---------------- t __export_symbol_simple_ring_buffer_reset ---------------- t __export_symbol_simple_ring_buffer_swap_reader_page ---------------- t __export_symbol_simple_ring_buffer_unload ---------------- T simple_ring_buffer_commit U simple_ring_buffer_commit ---------------- T simple_ring_buffer_enable_tracing U simple_ring_buffer_enable_tracing U simple_ring_buffer_init ---------------- T simple_ring_buffer_init ---------------- T simple_ring_buffer_init_mm ---------------- T simple_ring_buffer_reserve U simple_ring_buffer_reserve ---------------- T simple_ring_buffer_reset U simple_ring_buffer_reset U simple_ring_buffer_swap_reader_page ---------------- T simple_ring_buffer_swap_reader_page U simple_ring_buffer_unload ---------------- T simple_ring_buffer_unload ---------------- T simple_ring_buffer_unload_mm This is LLVM IR bitcode at this stage, which could be messing things up. $ file kernel/trace/simple_ring_buffer.o kernel/trace/simple_ring_buffer.o: LLVM IR bitcode Maybe not worth thinking about too much and just adding it to the allowlist manually? diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index 0f9a6ce9abd9..cb1ec50a8386 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -166,6 +166,7 @@ $(obj)/undefsyms_base.o: $(obj)/undefsyms_base.c targets += undefsyms_base.o UNDEFINED_ALLOWLIST = __asan __gcov __kasan __kcsan __hwasan __sanitizer __tsan __ubsan __x86_indirect_thunk \ + simple_ring_buffer \ $(shell $(NM) -u $(obj)/undefsyms_base.o 2>/dev/null | awk '{print $$2}') quiet_cmd_check_undefined = NM $< -- Cheers, Nathan ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] tracing: Generate undef symbols allowlist for simple_ring_buffer 2026-03-12 23:51 ` Nathan Chancellor @ 2026-03-13 10:23 ` Vincent Donnefort 0 siblings, 0 replies; 4+ messages in thread From: Vincent Donnefort @ 2026-03-13 10:23 UTC (permalink / raw) To: Nathan Chancellor Cc: maz, rostedt, arnd, linux-trace-kernel, kvmarm, kernel-team On Thu, Mar 12, 2026 at 04:51:53PM -0700, Nathan Chancellor wrote: > Hi Vincent, > > On Thu, Mar 12, 2026 at 06:20:10PM +0000, Vincent Donnefort wrote: > > Compiler and tooling-generated symbols are difficult to maintain > > across all supported architectures. Make the allowlist more robust by > > replacing the harcoded list with a mechanism that automatically detects > > these symbols. > > > > This mechanism generates a C function designed to trigger common > > compiler-inserted symbols. > > This certainly seems more robust. > > > Signed-off-by: Vincent Donnefort <vdonnefort@google.com> > > > > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile > > index beb15936829d..3b427b76434a 100644 > > --- a/kernel/trace/Makefile > > +++ b/kernel/trace/Makefile > > @@ -136,17 +136,37 @@ obj-$(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 '}' >> $@ > > This should use filechk, otherwise undefsyms_base.c will be regenerated > every build, resulting in undefsyms_base.o being rebuilt every time. > > $ make -skj"$(nproc)" ARCH=x86_64 mrproper allmodconfig kernel/trace/ > > $ make -skj"$(nproc)" ARCH=x86_64 V=2 kernel/trace/ > ... > CC kernel/trace/undefsyms_base.o - due to: kernel/trace/undefsyms_base.c > NM kernel/trace/simple_ring_buffer.o - due to target missing > > filechk_undefsyms_base = { \ > echo '$(pound)include <asm/page.h>'; \ > echo '$(pound)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 '}'; \ > } > > $(obj)/undefsyms_base.c: FORCE > $(call filechk,undefsyms_base) > > $ make -skj"$(nproc)" ARCH=x86_64 mrproper allmodconfig kernel/trace/ > > $ make -skj"$(nproc)" ARCH=x86_64 V=2 kernel/trace/ > GEN Makefile - due to target is PHONY > DESCEND objtool > CALL scripts/checksyscalls.sh - due to target is PHONY > INSTALL libsubcmd_headers > NM kernel/trace/simple_ring_buffer.o - due to target missing > > > +clean-files += undefsyms_base.c > > +targets += undefsyms_base.c > > I don't think this targets addition is necessary. > > > +$(obj)/undefsyms_base.o: $(obj)/undefsyms_base.c > > + > > +extra-y += undefsyms_base.o > > I think this should be > > targets += undefsyms_base.o > > as extra-y is deprecated per Documentation/kbuild/makefiles.rst. > > > +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}') > > With an allmodconfig + ThinLTO build, I still see: > > $ cat allmod.config > CONFIG_GCOV_KERNEL=n > CONFIG_KASAN=n > CONFIG_LTO_CLANG_THIN=y > > $ make -skj"$(nproc)" ARCH=x86_64 KCONFIG_ALLCONFIG=1 LLVM=1 mrproper allmodconfig kernel/trace/ > Unexpected symbols in kernel/trace/simple_ring_buffer.o: > U __fortify_panic > U __write_overflow_field > U simple_ring_buffer_commit > U simple_ring_buffer_enable_tracing > U simple_ring_buffer_init > U simple_ring_buffer_reserve > U simple_ring_buffer_reset > U simple_ring_buffer_swap_reader_page > U simple_ring_buffer_unload > > Something like: > > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile > index 48c415a0c7e4..0f9a6ce9abd9 100644 > --- a/kernel/trace/Makefile > +++ b/kernel/trace/Makefile > @@ -142,13 +142,15 @@ obj-$(CONFIG_TRACE_REMOTE_TEST) += remote_test.o > filechk_undefsyms_base = { \ > echo '$(pound)include <asm/page.h>'; \ > echo '$(pound)include <asm/local.h>'; \ > + echo '$(pound)include <linux/string.h>'; \ > echo 'static char page[PAGE_SIZE] __aligned(PAGE_SIZE);'; \ > - echo 'void undefsyms_base(int n);'; \ > - echo 'void undefsyms_base(int n) {'; \ > + echo 'void undefsyms_base(int n, void *ptr);'; \ > + echo 'void undefsyms_base(int n, void *ptr) {'; \ > 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)ptr, buffer, sizeof(buffer));'; \ > echo ' cmpxchg((u32 * volatile)&u, 0, 8);'; \ > echo ' WARN_ON(n == 0xdeadbeef);'; \ > echo '}'; \ > -- > > cures the first two. The simple_ring_buffer symbols are very odd... > > $ llvm-nm kernel/trace/simple_ring_buffer.o | grep simple_ring_buffer > ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_commit_845 > ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_enable_tracing_849 > ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_init_847 > ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_reserve_841 > ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_reset_846 > ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_swap_reader_page_837 > ---------------- d __UNIQUE_ID_addressable_simple_ring_buffer_unload_848 > ---------------- t __export_symbol_simple_ring_buffer_commit > ---------------- t __export_symbol_simple_ring_buffer_enable_tracing > ---------------- t __export_symbol_simple_ring_buffer_init > ---------------- t __export_symbol_simple_ring_buffer_reserve > ---------------- t __export_symbol_simple_ring_buffer_reset > ---------------- t __export_symbol_simple_ring_buffer_swap_reader_page > ---------------- t __export_symbol_simple_ring_buffer_unload > ---------------- T simple_ring_buffer_commit > U simple_ring_buffer_commit > ---------------- T simple_ring_buffer_enable_tracing > U simple_ring_buffer_enable_tracing > U simple_ring_buffer_init > ---------------- T simple_ring_buffer_init > ---------------- T simple_ring_buffer_init_mm > ---------------- T simple_ring_buffer_reserve > U simple_ring_buffer_reserve > ---------------- T simple_ring_buffer_reset > U simple_ring_buffer_reset > U simple_ring_buffer_swap_reader_page > ---------------- T simple_ring_buffer_swap_reader_page > U simple_ring_buffer_unload > ---------------- T simple_ring_buffer_unload > ---------------- T simple_ring_buffer_unload_mm > > This is LLVM IR bitcode at this stage, which could be messing things up. > > $ file kernel/trace/simple_ring_buffer.o > kernel/trace/simple_ring_buffer.o: LLVM IR bitcode > > Maybe not worth thinking about too much and just adding it to the > allowlist manually? That looks good, thanks for having a look. I'll spin a v2 with your comments. > > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile > index 0f9a6ce9abd9..cb1ec50a8386 100644 > --- a/kernel/trace/Makefile > +++ b/kernel/trace/Makefile > @@ -166,6 +166,7 @@ $(obj)/undefsyms_base.o: $(obj)/undefsyms_base.c > targets += undefsyms_base.o > > UNDEFINED_ALLOWLIST = __asan __gcov __kasan __kcsan __hwasan __sanitizer __tsan __ubsan __x86_indirect_thunk \ > + simple_ring_buffer \ > $(shell $(NM) -u $(obj)/undefsyms_base.o 2>/dev/null | awk '{print $$2}') > > quiet_cmd_check_undefined = NM $< > -- > > Cheers, > Nathan ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-03-13 10:23 UTC | newest] Thread overview: 4+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2026-03-12 18:20 [PATCH] tracing: Generate undef symbols allowlist for simple_ring_buffer Vincent Donnefort 2026-03-12 18:43 ` Steven Rostedt 2026-03-12 23:51 ` Nathan Chancellor 2026-03-13 10:23 ` Vincent Donnefort
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