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bpftool: Probe for bounded loop support

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This patch introduces a new probe to check whether the verifier supports
bounded loops as introduced in commit 2589726d12 ("bpf: introduce
bounded loops"). This patch will allow BPF users such as Cilium to probe
for loop support on startup and only unconditionally unroll loops on
older kernels.

The results are displayed as part of the miscellaneous section, as shown
below.

  $ bpftool feature probe | grep loops
  Bounded loop support is available
  $ bpftool feature probe macro | grep LOOPS
  #define HAVE_BOUNDED_LOOPS
  $ bpftool feature probe -j | jq .misc
  {
    "have_large_insn_limit": true,
    "have_bounded_loops": true
  }

Signed-off-by: Paul Chaignon <paul@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/f7807c0b27d79f48e71de7b5a99c680ca4bd0151.1641314075.git.paul@isovalent.com
This commit is contained in:
Paul Chaignon 2022-01-04 18:59:57 +01:00 committed by Daniel Borkmann
parent b22bf1b997
commit c04fb2b0bd
1 changed files with 22 additions and 0 deletions
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22
tools/bpf/bpftool/feature.c
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@ -687,6 +687,27 @@ static void probe_large_insn_limit(const char *define_prefix, __u32 ifindex)
"LARGE_INSN_LIMIT");
}
/*
* Probe for bounded loop support introduced in commit 2589726d12a1
* ("bpf: introduce bounded loops").
*/
static void
probe_bounded_loops(const char *define_prefix, __u32 ifindex)
{
struct bpf_insn insns[4] = {
BPF_MOV64_IMM(BPF_REG_0, 10),
BPF_ALU64_IMM(BPF_SUB, BPF_REG_0, 1),
BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, -2),
BPF_EXIT_INSN()
};
probe_misc_feature(insns, ARRAY_SIZE(insns),
define_prefix, ifindex,
"have_bounded_loops",
"Bounded loop support",
"BOUNDED_LOOPS");
}
static void
section_system_config(enum probe_component target, const char *define_prefix)
{
@ -801,6 +822,7 @@ static void section_misc(const char *define_prefix, __u32 ifindex)
"/*** eBPF misc features ***/",
define_prefix);
probe_large_insn_limit(define_prefix, ifindex);
probe_bounded_loops(define_prefix, ifindex);
print_end_section();
}