On Sat, Jul 13, 2024 at 12:43 AM Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Wed, Jul 10, 2024 at 10:45 PM <flyingpenghao@xxxxxxxxx> wrote: > > > > > > By tracing the call chain, we found that do_misc_fixups consumed a lot > > of stack space. mark it as noinline_for_stack to prevent it from spreading > > to bpf_check's stack size. > > ... > > -static int do_misc_fixups(struct bpf_verifier_env *env) > > +static noinline_for_stack int do_misc_fixups(struct bpf_verifier_env *env) > > Now we're getting somewhere, but this is not a fix. > It may shut up the warn, but it will only increase the total stack usage. > Looking at C code do_misc_fixups() needs ~200 bytes worth of stack > space for insn_buf[16] and spill/fill. > That's far from the artificial 2k limit. > > Please figure out what exact variable is causing kasan to consume > so much stack. You may need to analyze compiler internals and > do more homework. > What is before/after stack usage ? with and without kasan? > With gcc try > +CFLAGS_verifier.o += -fstack-usage > > I see: > sort -k2 -n kernel/bpf/verifier.su |tail -10 > ../kernel/bpf/verifier.c:13087:12:adjust_ptr_min_max_vals 240 > dynamic,bounded > ../kernel/bpf/verifier.c:20804:12:do_check_common 248 dynamic,bounded > ../kernel/bpf/verifier.c:19151:12:convert_ctx_accesses 256 static > ../kernel/bpf/verifier.c:7450:12:check_mem_reg 256 static > ../kernel/bpf/verifier.c:7482:12:check_kfunc_mem_size_reg 256 static > ../kernel/bpf/verifier.c:10268:12:check_helper_call.isra 272 > dynamic,bounded > ../kernel/bpf/verifier.c:21562:5:bpf_check 296 dynamic,bounded > ../kernel/bpf/verifier.c:19860:12:do_misc_fixups 320 static > ../kernel/bpf/verifier.c:13991:12:adjust_reg_min_max_vals 392 static > ../kernel/bpf/verifier.c:12280:12:check_kfunc_call.isra 408 > dynamic,bounded > > do_misc_fixups() is not the smallest, but not that large either. > If I use gcc, I get the same result as you, but if I use llvm to build the kernel, the result is like this： # sort -k2 -n kernel/bpf/verifier.su | tail -10 kernel/bpf/verifier.c:14026:adjust_reg_min_max_vals 440 static kernel/bpf/verifier.c:7432:check_mem_reg 440 static kernel/bpf/verifier.c:15955:check_cfg 472 static kernel/bpf/verifier.c:7464:check_kfunc_mem_size_reg 472 static kernel/bpf/verifier.c:15104:check_cond_jmp_op 504 static kernel/bpf/verifier.c:4166:__mark_chain_precision 504 static kernel/bpf/verifier.c:10239:check_helper_call 536 static kernel/bpf/verifier.c:17744:do_check 792 static kernel/bpf/verifier.c:12248:check_kfunc_call 984 static kernel/bpf/verifier.c:21486:bpf_check 2456 static Obviously, do_misc_fixups is automatically inlined into bpf_check. So adding noinline_for_stack to the do_misc_fixups function is a solution. Thanks. > Do in-depth analysis instead of silencing the warn. > > pw-bot: cr
