I'm trying to build a BPF program written in C into the bpf bytecode needed to load it. I used this post to try to start me off: https://blogs.oracle.com/linux/notes-on-bpf-4
I do not want to use BCC due to the library dependency. I'm using ubuntu 18.04 (Linux bpf-ubuntu 4.15.0-1036-gcp #38-Ubuntu SMP Mon Jun 24 13:49:05 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux)
My file is super simple (and possibly incorrect) at the moment as I'm still trying to get compiling to work:
#include <linux/version.h>
#include <uapi/linux/bpf.h>
#include "bpf_helpers.h"
#include <net/sock.h>
SEC("kprobe/tcp_connect")
int bpf_prog1(struct pt_regs *ctx) {
struct sock *sk;
sk = (struct sock*) PT_REGS_PARM1(ctx);
bpf_trace_printk("%s\n","Got tcp_connect");
}
char _license[] SEC("license") = "GPL";
u32 _version SEC("version") = LINUX_VERSION_CODE;
The command being used to build and result is:
clang -nostdinc -isystem `clang -print-file-name=include` \
-D__KERNEL__ -D__ASM_SYSREG_H \
-Wno-unused-value -Wno-pointer-sign \
-Wno-compare-distinct-pointer-types \
-Wno-gnu-variable-sized-type-not-at-end \
-Wno-address-of-packed-member -Wno-tautological-compare \
-Wno-unknown-warning-option \
-I../include -I/usr/src/linux-headers-`uname -r`/include -I/usr/src/linux-headers-`uname -r`/arch/x86/include -I/usr/src/linux-headers-`uname -r`/arch/x86/include/uapi -I/usr/src/linux-headers-`uname -r`/arch/x86/include/generated/uapi -I/usr/src/linux-headers-`uname -r`/include/generated/uapi -I/usr/src/linux-headers-`uname -r`/include/uapi \
-O2 -emit-llvm -c net_mon_kern.c -o -| llc -march=bpf -filetype=obj -o net_mon_kern.o
In file included from net_mon_kern.c:7:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/net/sock.h:43:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/hardirq.h:5:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/preempt.h:11:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/list.h:9:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/kernel.h:11:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/bitops.h:18:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/bitops.h:514:
/usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/arch_hweight.h:55:42: error: expected ')'
asm (ALTERNATIVE("call __sw_hweight64", POPCNT64, X86_FEATURE_POPCNT)
^
/usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/arch_hweight.h:55:6: note: to match this '('
asm (ALTERNATIVE("call __sw_hweight64", POPCNT64, X86_FEATURE_POPCNT)
^
In file included from net_mon_kern.c:7:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/net/sock.h:43:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/hardirq.h:5:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/preempt.h:81:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/preempt.h:7:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/thread_info.h:38:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/thread_info.h:12:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/page.h:14:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/page_32.h:35:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/string.h:19:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/string.h:5:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/string_64.h:6:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/jump_label.h:188:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/include/linux/atomic.h:5:
In file included from /usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/atomic.h:276:
/usr/src/linux-headers-4.15.0-1036-gcp/arch/x86/include/asm/atomic64_64.h:20:40: error: unknown type name
'atomic64_t'; did you mean 'atomic_t'?
static inline long atomic64_read(const atomic64_t *v)
^~~~~~~~~~
atomic_t
/usr/src/linux-headers-4.15.0-1036-gcp/include/linux/types.h:178:3: note: 'atomic_t' declared here
} atomic_t;
^
18 more errors relating to atomic64_t...
I'm not really sure how to troubleshoot that. I can only assume the way I'm including the headers is not correct.
TL;DR: Try including linux/kconfig.h before your other includes.
It looks to me that your command line is inspired from the kernel samples (under samples/bpf/), but that you try to compile out of the tree, and you trimmed the non-relevant bits.
What happens when you try to compile your code is that clang gets all relevant kernel headers at the paths you passed with the -I options. However, a number of those headers contain conditional definitions or inclusions, depending on the requested configuration for the kernel to build. For example, include/linux/types.h, which is eventually included through <net/sock.h>, has this code:
#ifdef CONFIG_64BIT
typedef struct {
long counter;
} atomic64_t;
#endif
But when you compile, CONFIG_64BIT has never been defined... I let you relate with the error message you obtained :).
The kernel samples actually include kconfig.h through LINUXINCLUDE and USERINCLUDE, so we must find a way to add it somehow. This is apparently sufficient to get the configuration variables set correctly and to fix the compilation issues.
I found the following possibilities to include the file in your case:
#include <linux/kconfig.h> to your file, before including the other kernel headers (e.g. on the first line).-include linux/kconfig.h, like kernel samples do (which seems the cleanest way).