On Tue, Sep 1, 2020 at 11:12 AM Andrii Nakryiko andrii.nakryiko@gmail.com wrote:
On Thu, Aug 27, 2020 at 8:42 PM Hao Luo haoluo@google.com wrote:
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-extern const struct rq runqueues __ksym; /* struct type global var. */ +extern const struct rq runqueues __ksym; /* struct type percpu var. */ extern const int bpf_prog_active __ksym; /* int type global var. */ +extern const unsigned long process_counts __ksym; /* int type percpu var. */
SEC("raw_tp/sys_enter") int handler(const void *ctx) {
struct rq *rq;unsigned long *count;out__runqueues = (__u64)&runqueues; out__bpf_prog_active = (__u64)&bpf_prog_active;rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, 1);if (rq)out__rq_cpu = rq->cpu;this is awesome!
Are there any per-cpu variables that are arrays? Would be nice to test those too.
There are currently per-cpu arrays, but not common. There is a 'pmc_prev_left' in arch/x86, I can add that in this test.
arch-specific variables are bad, because selftests will be failing on other architectures; let's not do this then.
Yeah, no problem. Though not going to add this arch-specific variable in the posted patches, I tried array-typed ksyms locally in my test environment. It worked fine, except that the array size is not checked. For instance, if there is a percpu array in kernel as
DEFINE_PER_CPU(u32[64], foo);
we can declare a ksym of different size and it passes libbpf checks and kernel verification.
extern u32 foo[128] __ksyms;
It seems that bpf_core_types_are_compat() doesn't check nr_elem. But it seems the kernel verifier does check out-of-bounds accesses, so this may not be a real problem. Just want to list what I saw.
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