Bcc: Compiling and loading eBPF programs not possible after LLVM /clang upgrade

[computer5student]

Hi,

until a few days ago everything on my system was working. Now I cannot load eBPF programs anymore because I get the error message below. I updates the following things:

• kernel upgrade (but with my old kernel, 4.16.0-rc4+ it does not work either now),
• NIC driver (which is not involved up to this point)
• probably clang / LLVM by entering "apt get update" and "apt get upgrade"

bcc version: (0.5.0-300.git.5d23500)
Linux kernel: 4.16.0+
OS: Ubuntu 17.10
clang version 7.0.0- (trunk)

In file included from /virtual/main.c:2:
In file included from /lib/modules/4.16.0+/build/include/linux/blkdev.h:5:
In file included from /lib/modules/4.16.0+/build/include/linux/sched.h:14:
In file included from /lib/modules/4.16.0+/build/include/linux/pid.h:5:
In file included from /lib/modules/4.16.0+/build/include/linux/rculist.h:11:
In file included from /lib/modules/4.16.0+/build/include/linux/rcupdate.h:40:
In file included from /lib/modules/4.16.0+/build/include/linux/preempt.h:81:
In file included from /lib/modules/4.16.0+/build/arch/x86/include/asm/preempt.h:7:
In file included from /lib/modules/4.16.0+/build/include/linux/thread_info.h:38:
In file included from /lib/modules/4.16.0+/build/arch/x86/include/asm/thread_info.h:53:
/lib/modules/4.16.0+/build/arch/x86/include/asm/cpufeature.h:150:2: error: expected '(' after 'asm'
asm_volatile_goto("1: jmp 6fn"
^
/lib/modules/4.16.0+/build/include/linux/compiler-gcc.h:296:42: note: expanded from macro 'asm_volatile_goto'

define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)

                                     ^

1 error generated.

[yonghong-song]

This is a known issue for latest linux. The reason is that
clang does not support asm goto.

It is introduced by the following commit:
commit d0266046ad54e0c964941364cd82a0d0478ce286
Author: Peter Zijlstra [e-mail]
Date: Mon Mar 19 16:41:26 2018 +0100

x86: Remove FAST_FEATURE_TESTS

Since we want to rely on static branches to avoid speculation, remove
any possible fallback code for static_cpu_has.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]

You can use the following workaround:
diff --git a/arch/x86/include/asm/cpufeature.h
b/arch/x86/include/asm/cpufeature.h
index b27da96..71e02c4 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -140,6 +140,7 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c,
unsigned int bit);

#define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)

+#if 0
/*

• Static testing of CPU features. Used the same as boot_cpu_has().
• These will statically patch the target code for additional
  @@ -195,6 +196,9 @@ static __always_inline __pure bool _static_cpu_has(u16 bit)
  boot_cpu_has(bit) :
  _static_cpu_has(bit)
  )
  +#else
  +#define static_cpu_has(bit) boot_cpu_has(bit)
  +#endif

#define cpu_has_bug(c, bit) cpu_has(c, (bit))
#define set_cpu_bug(c, bit) set_cpu_cap(c, (bit))

I will dig into a little more here to see what we can do.

On Tue, Apr 10, 2018 at 5:34 AM, computer5student
[e-mail] wrote:

Hi,

until a few days ago everything on my system was working. Now I cannot load
eBPF programs anymore because I get the error message below. I updates the
following things:

kernel upgrade (but with my old kernel, 4.16.0-rc4+ it does not work either
now),
NIC driver (which is not involved up to this point)
probably clang / LLVM by entering "apt get update" and "apt get upgrade"

bcc version: (0.5.0-300.git.5d23500)
Linux kernel: 4.16.0+
OS: Ubuntu 17.10
clang version 7.0.0- (trunk)

In file included from /virtual/main.c:2:
In file included from /lib/modules/4.16.0+/build/include/linux/blkdev.h:5:
In file included from /lib/modules/4.16.0+/build/include/linux/sched.h:14:
In file included from /lib/modules/4.16.0+/build/include/linux/pid.h:5:
In file included from /lib/modules/4.16.0+/build/include/linux/rculist.h:11:
In file included from
/lib/modules/4.16.0+/build/include/linux/rcupdate.h:40:
In file included from /lib/modules/4.16.0+/build/include/linux/preempt.h:81:
In file included from
/lib/modules/4.16.0+/build/arch/x86/include/asm/preempt.h:7:
In file included from
/lib/modules/4.16.0+/build/include/linux/thread_info.h:38:
In file included from
/lib/modules/4.16.0+/build/arch/x86/include/asm/thread_info.h:53:
/lib/modules/4.16.0+/build/arch/x86/include/asm/cpufeature.h:150:2: error:
expected '(' after 'asm'
asm_volatile_goto("1: jmp 6fn"
^
/lib/modules/4.16.0+/build/include/linux/compiler-gcc.h:296:42: note:
expanded from macro 'asm_volatile_goto'

define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)

^
1 error generated.

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[computer5student]

Thank you very much, that indeed fixes the problem.