From 341dfcf8d78eaa3a2dc96dea06f0392eb2978364 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Mon, 12 Aug 2019 11:39:47 -0700 Subject: btf: expose BTF info through sysfs Make .BTF section allocated and expose its contents through sysfs. /sys/kernel/btf directory is created to contain all the BTFs present inside kernel. Currently there is only kernel's main BTF, represented as /sys/kernel/btf/kernel file. Once kernel modules' BTFs are supported, each module will expose its BTF as /sys/kernel/btf/ file. Current approach relies on a few pieces coming together: 1. pahole is used to take almost final vmlinux image (modulo .BTF and kallsyms) and generate .BTF section by converting DWARF info into BTF. This section is not allocated and not mapped to any segment, though, so is not yet accessible from inside kernel at runtime. 2. objcopy dumps .BTF contents into binary file and subsequently convert binary file into linkable object file with automatically generated symbols _binary__btf_kernel_bin_start and _binary__btf_kernel_bin_end, pointing to start and end, respectively, of BTF raw data. 3. final vmlinux image is generated by linking this object file (and kallsyms, if necessary). sysfs_btf.c then creates /sys/kernel/btf/kernel file and exposes embedded BTF contents through it. This allows, e.g., libbpf and bpftool access BTF info at well-known location, without resorting to searching for vmlinux image on disk (location of which is not standardized and vmlinux image might not be even available in some scenarios, e.g., inside qemu during testing). Alternative approach using .incbin assembler directive to embed BTF contents directly was attempted but didn't work, because sysfs_proc.o is not re-compiled during link-vmlinux.sh stage. This is required, though, to update embedded BTF data (initially empty data is embedded, then pahole generates BTF info and we need to regenerate sysfs_btf.o with updated contents, but it's too late at that point). If BTF couldn't be generated due to missing or too old pahole, sysfs_btf.c handles that gracefully by detecting that _binary__btf_kernel_bin_start (weak symbol) is 0 and not creating /sys/kernel/btf at all. v2->v3: - added Documentation/ABI/testing/sysfs-kernel-btf (Greg K-H); - created proper kobject (btf_kobj) for btf directory (Greg K-H); - undo v2 change of reusing vmlinux, as it causes extra kallsyms pass due to initially missing __binary__btf_kernel_bin_{start/end} symbols; v1->v2: - allow kallsyms stage to re-use vmlinux generated by gen_btf(); Reviewed-by: Greg Kroah-Hartman Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann --- scripts/link-vmlinux.sh | 52 +++++++++++++++++++++++++++++++------------------ 1 file changed, 33 insertions(+), 19 deletions(-) (limited to 'scripts/link-vmlinux.sh') diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh index a7124f895b24..cb93832c6ad7 100755 --- a/scripts/link-vmlinux.sh +++ b/scripts/link-vmlinux.sh @@ -56,8 +56,8 @@ modpost_link() } # Link of vmlinux -# ${1} - optional extra .o files -# ${2} - output file +# ${1} - output file +# ${@:2} - optional extra .o files vmlinux_link() { local lds="${objtree}/${KBUILD_LDS}" @@ -70,9 +70,9 @@ vmlinux_link() --start-group \ ${KBUILD_VMLINUX_LIBS} \ --end-group \ - ${1}" + ${@:2}" - ${LD} ${KBUILD_LDFLAGS} ${LDFLAGS_vmlinux} -o ${2} \ + ${LD} ${KBUILD_LDFLAGS} ${LDFLAGS_vmlinux} -o ${1} \ -T ${lds} ${objects} else objects="-Wl,--whole-archive \ @@ -81,9 +81,9 @@ vmlinux_link() -Wl,--start-group \ ${KBUILD_VMLINUX_LIBS} \ -Wl,--end-group \ - ${1}" + ${@:2}" - ${CC} ${CFLAGS_vmlinux} -o ${2} \ + ${CC} ${CFLAGS_vmlinux} -o ${1} \ -Wl,-T,${lds} \ ${objects} \ -lutil -lrt -lpthread @@ -92,23 +92,34 @@ vmlinux_link() } # generate .BTF typeinfo from DWARF debuginfo +# ${1} - vmlinux image +# ${2} - file to dump raw BTF data into gen_btf() { - local pahole_ver; + local pahole_ver + local bin_arch if ! [ -x "$(command -v ${PAHOLE})" ]; then info "BTF" "${1}: pahole (${PAHOLE}) is not available" - return 0 + return 1 fi pahole_ver=$(${PAHOLE} --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/') if [ "${pahole_ver}" -lt "113" ]; then info "BTF" "${1}: pahole version $(${PAHOLE} --version) is too old, need at least v1.13" - return 0 + return 1 fi - info "BTF" ${1} + info "BTF" ${2} + vmlinux_link ${1} LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} + + # dump .BTF section into raw binary file to link with final vmlinux + bin_arch=$(${OBJDUMP} -f ${1} | grep architecture | \ + cut -d, -f1 | cut -d' ' -f2) + ${OBJCOPY} --dump-section .BTF=.btf.kernel.bin ${1} 2>/dev/null + ${OBJCOPY} -I binary -O ${CONFIG_OUTPUT_FORMAT} -B ${bin_arch} \ + --rename-section .data=.BTF .btf.kernel.bin ${2} } # Create ${2} .o file with all symbols from the ${1} object file @@ -153,6 +164,7 @@ sortextable() # Delete output files in case of error cleanup() { + rm -f .btf.* rm -f .tmp_System.map rm -f .tmp_kallsyms* rm -f .tmp_vmlinux* @@ -215,6 +227,13 @@ ${MAKE} -f "${srctree}/scripts/Makefile.modpost" vmlinux.o info MODINFO modules.builtin.modinfo ${OBJCOPY} -j .modinfo -O binary vmlinux.o modules.builtin.modinfo +btf_kernel_bin_o="" +if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then + if gen_btf .tmp_vmlinux.btf .btf.kernel.bin.o ; then + btf_kernel_bin_o=.btf.kernel.bin.o + fi +fi + kallsymso="" kallsyms_vmlinux="" if [ -n "${CONFIG_KALLSYMS}" ]; then @@ -246,11 +265,11 @@ if [ -n "${CONFIG_KALLSYMS}" ]; then kallsyms_vmlinux=.tmp_vmlinux2 # step 1 - vmlinux_link "" .tmp_vmlinux1 + vmlinux_link .tmp_vmlinux1 ${btf_kernel_bin_o} kallsyms .tmp_vmlinux1 .tmp_kallsyms1.o # step 2 - vmlinux_link .tmp_kallsyms1.o .tmp_vmlinux2 + vmlinux_link .tmp_vmlinux2 .tmp_kallsyms1.o ${btf_kernel_bin_o} kallsyms .tmp_vmlinux2 .tmp_kallsyms2.o # step 3 @@ -261,18 +280,13 @@ if [ -n "${CONFIG_KALLSYMS}" ]; then kallsymso=.tmp_kallsyms3.o kallsyms_vmlinux=.tmp_vmlinux3 - vmlinux_link .tmp_kallsyms2.o .tmp_vmlinux3 - + vmlinux_link .tmp_vmlinux3 .tmp_kallsyms2.o ${btf_kernel_bin_o} kallsyms .tmp_vmlinux3 .tmp_kallsyms3.o fi fi info LD vmlinux -vmlinux_link "${kallsymso}" vmlinux - -if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then - gen_btf vmlinux -fi +vmlinux_link vmlinux "${kallsymso}" "${btf_kernel_bin_o}" if [ -n "${CONFIG_BUILDTIME_EXTABLE_SORT}" ]; then info SORTEX vmlinux -- cgit v1.2.3