Hi Manu,
On Fri, Feb 02, 2024 at 03:09:05PM -0800, Manu Bretelle wrote:
On Sun, Jan 28, 2024 at 06:24:05PM -0700, Daniel Xu wrote:
=== Description ===
This is a bpf-treewide change that annotates all kfuncs as such inside .BTF_ids. This annotation eventually allows us to automatically generate kfunc prototypes from bpftool.
We store this metadata inside a yet-unused flags field inside struct btf_id_set8 (thanks Kumar!). pahole will be taught where to look.
More details about the full chain of events are available in commit 3's description.
The accompanying pahole and bpftool changes can be viewed here on these "frozen" branches [0][1].
I hit a similar issue to [0] on master 943b043aeecc ("selftests/bpf: Fix bench runner SIGSEGV") when cross-compiling on x86_64 (LE) to s390x (BE). I do have CONFIG_DEBUG_INFO_BTF enable and the issue would not trigger if I disabled CONFIG_DEBUG_INFO_BTF (and with the fix mentioned in [0]).
What seems to happen is that `tools/resolve_btfids` is ran in the context of the host endianess and if I printk before the WARN_ON: diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index ef380e546952..a9ed7a1a4936 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -8128,6 +8128,7 @@ int register_btf_kfunc_id_set(enum bpf_prog_type prog_type, * WARN() for initcall registrations that do not check errors. */ if (!(kset->set->flags & BTF_SET8_KFUNCS)) {
printk("Flag 0x%08X, expected 0x%08X\n", kset->set->flags, BTF_SET8_KFUNCS); WARN_ON(!kset->owner); return -EINVAL; }the boot logs would show: Flag 0x01000000, expected 0x00000001
The issue did not happen prior to 6f3189f38a3e ("bpf: treewide: Annotate BPF kfuncs in BTF") has only 0 was written before.
It seems [1] will be addressing cross-compilation, but it did not fix it as is by just applying on top of master, so probably some of the changes will also need to be ported to `tools/include/linux/btf_ids.h`?
A hacky workaround to cross-compilation I have is to apply:
diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile index 4b8079f294f6..b706e7ab066f 100644 --- a/tools/bpf/resolve_btfids/Makefile +++ b/tools/bpf/resolve_btfids/Makefile @@ -22,10 +22,10 @@ HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH) CROSS_COMPILE="" EXTRA_CFLAGS="$(HOSTCFLAGS)" RM ?= rm -HOSTCC ?= gcc -HOSTLD ?= ld -HOSTAR ?= ar -CROSS_COMPILE = +HOSTCC = $(CC) +HOSTLD = $(LD) +HOSTAR = $(AR) +#CROSS_COMPILE = OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/ @@ -56,16 +56,16 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT): $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd $(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
DESTDIR=$(SUBCMD_DESTDIR) prefix= subdir= \ $(abspath $@) install_headers$(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT) $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT) \
DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
DESTDIR=$(LIBBPF_DESTDIR) prefix= subdir= \ $(abspath $@) install_headers-LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null) -LIBELF_LIBS := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf) +LIBELF_FLAGS := $(shell $(PKG_CONFIG) libelf --cflags 2>/dev/null) +LIBELF_LIBS := $(shell $(PKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf) HOSTCFLAGS_resolve_btfids += -g \ -I$(srctree)/tools/include \ @@ -84,7 +84,7 @@ $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT) $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN) $(call msg,LINK,$@)
$(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
$(Q)$(CC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)clean_objects := $(wildcard $(OUTPUT)/*.o \ $(OUTPUT)/.*.o.cmd \ diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index a38a3001527c..5cd193c04448 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -171,7 +171,7 @@ INCLUDE_DIR := $(SCRATCH_DIR)/include BPFOBJ := $(BUILD_DIR)/libbpf/libbpf.a ifneq ($(CROSS_COMPILE),) HOST_BUILD_DIR := $(BUILD_DIR)/host -HOST_SCRATCH_DIR := $(OUTPUT)/host-tools +HOST_SCRATCH_DIR := $(SCRATCH_DIR) HOST_INCLUDE_DIR := $(HOST_SCRATCH_DIR)/include else HOST_BUILD_DIR := $(BUILD_DIR)
This causes `resolve_btfids` to be compiled in the target endianess and gets magically run provided that the hosts has `qemu-s390x-static` and a functional binfmt_misc [2] on the host, but having this using host architecture per [1] is likely better.
This is kinda surprising to me. I don't recall seeing any code inside resolve_btfids that touches the set8 flags field -- only the ids in the flexible array member. Would be interested to see what the value of the set8 flags field is before resolve_btfids is run.
I'm a bit busy until Sunday afternoon but I'll try to take a look around then. Might be a good opportunity to play with poke [0].
Thanks, Daniel