Hello. I changed the hook as below and confirmed that cp == NULL at bpf_probe_read(). That is, it is bpf_usdt_readarg() which got broken.
---------- int do_start(struct pt_regs *ctx) { char *cp = NULL; bpf_usdt_readarg(1, ctx, &cp); struct { char query[QUERY_MAX]; } data = { }; if (cp != NULL) bpf_probe_read(&data.query, sizeof(data.query), (void *) cp); else data.query[0] = '!'; events.perf_submit(ctx, &data, sizeof(data)); return 0; }; ---------- If I do - std::string cptr = tfm::format("*((volatile %s *)dest)", ctype); + std::string cptr = tfm::format("*((%s *)dest)", ctype); (i.e. drop only "volatile " part) in that commit like below ---------- diff --git a/src/cc/usdt.cc b/src/cc/usdt.cc --- a/src/cc/usdt.cc +++ b/src/cc/usdt.cc @@ -152,7 +152,7 @@ bool Probe::usdt_getarg(std::ostream &stream) { for (size_t arg_n = 0; arg_n < arg_count; ++arg_n) { std::string ctype = largest_arg_type(arg_n); - std::string cptr("dest"); + std::string cptr = tfm::format("*((%s *)dest)", ctype); tfm::format(stream, "static __always_inline int _bpf_readarg_%s_%d(" ---------- USDT probe works again as well as build warning shown below goes away. ---------- /virtual/main.c:4:8: warning: incompatible integer to pointer conversion assigning to 'void *' from 'volatile uint64_t' (aka 'volatile unsigned long long') [-Wint-conversion] dest = *(volatile uint64_t *)&ctx->bx; ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ---------- _______________________________________________ iovisor-dev mailing list iovisor-dev@lists.iovisor.org https://lists.iovisor.org/mailman/listinfo/iovisor-dev