Commit 72ef80b5 authored by Daniel Borkmann's avatar Daniel Borkmann
Browse files

Merge branch 'bpf-libbpf-read-sysfs-btf' 



Andrii Nakryiko says:

====================
Now that kernel's BTF is exposed through sysfs at well-known location, attempt
to load it first as a target BTF for the purpose of BPF CO-RE relocations.

Patch #1 is a follow-up patch to rename /sys/kernel/btf/kernel into
/sys/kernel/btf/vmlinux.

Patch #2 adds ability to load raw BTF contents from sysfs and expands the list
of locations libbpf attempts to load vmlinux BTF from.
====================

Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parents 9840a4ff a1916a15

Documentation/ABI/testing/sysfs-kernel-btf

+1 −1
Original line number Diff line number Diff line
@@ -6,7 +6,7 @@ Description: 
		Contains BTF type information and related data for kernel and

		kernel modules.



What:		/sys/kernel/btf/kernel

What:		/sys/kernel/btf/vmlinux

Date:		Aug 2019

KernelVersion:	5.5

Contact:	bpf@vger.kernel.org

kernel/bpf/sysfs_btf.c

+15 −15
Original line number Diff line number Diff line
@@ -9,30 +9,30 @@ 
#include <linux/sysfs.h>



/* See scripts/link-vmlinux.sh, gen_btf() func for details */

extern char __weak _binary__btf_kernel_bin_start[];

extern char __weak _binary__btf_kernel_bin_end[];

extern char __weak _binary__btf_vmlinux_bin_start[];

extern char __weak _binary__btf_vmlinux_bin_end[];



static ssize_t

btf_kernel_read(struct file *file, struct kobject *kobj,

btf_vmlinux_read(struct file *file, struct kobject *kobj,

		 struct bin_attribute *bin_attr,

		 char *buf, loff_t off, size_t len)

{

	memcpy(buf, _binary__btf_kernel_bin_start + off, len);

	memcpy(buf, _binary__btf_vmlinux_bin_start + off, len);

	return len;

}



static struct bin_attribute bin_attr_btf_kernel __ro_after_init = {

	.attr = { .name = "kernel", .mode = 0444, },

	.read = btf_kernel_read,

static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {

	.attr = { .name = "vmlinux", .mode = 0444, },

	.read = btf_vmlinux_read,

};



static struct kobject *btf_kobj;



static int __init btf_kernel_init(void)

static int __init btf_vmlinux_init(void)

{

	int err;



	if (!_binary__btf_kernel_bin_start)

	if (!_binary__btf_vmlinux_bin_start)

		return 0;



	btf_kobj = kobject_create_and_add("btf", kernel_kobj);
@@ -42,10 +42,10 @@ static int __init btf_kernel_init(void) 
		return err;

	}



	bin_attr_btf_kernel.size = _binary__btf_kernel_bin_end -

				   _binary__btf_kernel_bin_start;

	bin_attr_btf_vmlinux.size = _binary__btf_vmlinux_bin_end -

				    _binary__btf_vmlinux_bin_start;



	return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_kernel);

	return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);

}



subsys_initcall(btf_kernel_init);
 
subsys_initcall(btf_vmlinux_init);

scripts/link-vmlinux.sh

+9 −9
Original line number Diff line number Diff line
@@ -117,9 +117,9 @@ gen_btf() 
	# 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} --dump-section .BTF=.btf.vmlinux.bin ${1} 2>/dev/null

	${OBJCOPY} -I binary -O ${CONFIG_OUTPUT_FORMAT} -B ${bin_arch} \

		--rename-section .data=.BTF .btf.kernel.bin ${2}

		--rename-section .data=.BTF .btf.vmlinux.bin ${2}

}



# Create ${2} .o file with all symbols from the ${1} object file
@@ -227,10 +227,10 @@ ${MAKE} -f "${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=""

btf_vmlinux_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

	if gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then

		btf_vmlinux_bin_o=.btf.vmlinux.bin.o

	fi

fi
@@ -265,11 +265,11 @@ if [ -n "${CONFIG_KALLSYMS}" ]; then 
	kallsyms_vmlinux=.tmp_vmlinux2



	# step 1

	vmlinux_link .tmp_vmlinux1 ${btf_kernel_bin_o}

	vmlinux_link .tmp_vmlinux1 ${btf_vmlinux_bin_o}

	kallsyms .tmp_vmlinux1 .tmp_kallsyms1.o



	# step 2

	vmlinux_link .tmp_vmlinux2 .tmp_kallsyms1.o ${btf_kernel_bin_o}

	vmlinux_link .tmp_vmlinux2 .tmp_kallsyms1.o ${btf_vmlinux_bin_o}

	kallsyms .tmp_vmlinux2 .tmp_kallsyms2.o



	# step 3
@@ -280,13 +280,13 @@ if [ -n "${CONFIG_KALLSYMS}" ]; then 
		kallsymso=.tmp_kallsyms3.o

		kallsyms_vmlinux=.tmp_vmlinux3



		vmlinux_link .tmp_vmlinux3 .tmp_kallsyms2.o ${btf_kernel_bin_o}

		vmlinux_link .tmp_vmlinux3 .tmp_kallsyms2.o ${btf_vmlinux_bin_o}

		kallsyms .tmp_vmlinux3 .tmp_kallsyms3.o

	fi

fi



info LD vmlinux

vmlinux_link vmlinux "${kallsymso}" "${btf_kernel_bin_o}"

vmlinux_link vmlinux "${kallsymso}" "${btf_vmlinux_bin_o}"



if [ -n "${CONFIG_BUILDTIME_EXTABLE_SORT}" ]; then

	info SORTEX vmlinux

tools/lib/bpf/libbpf.c

+57 −7
Original line number Diff line number Diff line
@@ -2807,15 +2807,61 @@ static int bpf_core_reloc_insn(struct bpf_program *prog, int insn_off, 
	return 0;

}



static struct btf *btf_load_raw(const char *path)

{

	struct btf *btf;

	size_t read_cnt;

	struct stat st;

	void *data;

	FILE *f;



	if (stat(path, &st))

		return ERR_PTR(-errno);



	data = malloc(st.st_size);

	if (!data)

		return ERR_PTR(-ENOMEM);



	f = fopen(path, "rb");

	if (!f) {

		btf = ERR_PTR(-errno);

		goto cleanup;

	}



	read_cnt = fread(data, 1, st.st_size, f);

	fclose(f);

	if (read_cnt < st.st_size) {

		btf = ERR_PTR(-EBADF);

		goto cleanup;

	}



	btf = btf__new(data, read_cnt);



cleanup:

	free(data);

	return btf;

}



/*

 * Probe few well-known locations for vmlinux kernel image and try to load BTF

 * data out of it to use for target BTF.

 */

static struct btf *bpf_core_find_kernel_btf(void)

{

	const char *locations[] = {

		"/lib/modules/%1$s/vmlinux-%1$s",

		"/usr/lib/modules/%1$s/kernel/vmlinux",

	struct {

		const char *path_fmt;

		bool raw_btf;

	} locations[] = {

		/* try canonical vmlinux BTF through sysfs first */

		{ "/sys/kernel/btf/vmlinux", true /* raw BTF */ },

		/* fall back to trying to find vmlinux ELF on disk otherwise */

		{ "/boot/vmlinux-%1$s" },

		{ "/lib/modules/%1$s/vmlinux-%1$s" },

		{ "/lib/modules/%1$s/build/vmlinux" },

		{ "/usr/lib/modules/%1$s/kernel/vmlinux" },

		{ "/usr/lib/debug/boot/vmlinux-%1$s" },

		{ "/usr/lib/debug/boot/vmlinux-%1$s.debug" },

		{ "/usr/lib/debug/lib/modules/%1$s/vmlinux" },

	};

	char path[PATH_MAX + 1];

	struct utsname buf;
@@ -2825,14 +2871,18 @@ static struct btf *bpf_core_find_kernel_btf(void) 
	uname(&buf);



	for (i = 0; i < ARRAY_SIZE(locations); i++) {

		snprintf(path, PATH_MAX, locations[i], buf.release);

		snprintf(path, PATH_MAX, locations[i].path_fmt, buf.release);



		if (access(path, R_OK))

			continue;



		if (locations[i].raw_btf)

			btf = btf_load_raw(path);

		else

			btf = btf__parse_elf(path, NULL);

		pr_debug("kernel BTF load from '%s': %ld\n",

			 path, PTR_ERR(btf));



		pr_debug("loading kernel BTF '%s': %ld\n",

			 path, IS_ERR(btf) ? PTR_ERR(btf) : 0);

		if (IS_ERR(btf))

			continue;

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