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: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Daniel Borkmann 2019-08-13 23:19:42 +02:00
commit 72ef80b5ee
4 changed files with 82 additions and 32 deletions

View File

@ -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

View File

@ -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,
struct bin_attribute *bin_attr,
char *buf, loff_t off, size_t len)
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);

View File

@ -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

View File

@ -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;
btf = btf__parse_elf(path, NULL);
pr_debug("kernel BTF load from '%s': %ld\n",
path, PTR_ERR(btf));
if (locations[i].raw_btf)
btf = btf_load_raw(path);
else
btf = btf__parse_elf(path, NULL);
pr_debug("loading kernel BTF '%s': %ld\n",
path, IS_ERR(btf) ? PTR_ERR(btf) : 0);
if (IS_ERR(btf))
continue;