From b9b4b1cef156e6b403b26ea4cb6d0caf4850e05c Mon Sep 17 00:00:00 2001 From: Michael Holzheu Date: Wed, 29 Apr 2015 18:45:03 +0200 Subject: [PATCH] s390/bpf: Fix gcov stack space problem When compiling the kernel for GCOV (CONFIG_GCOV_KERNEL,-fprofile-arcs), gcc allocates a lot of stack space because of the large switch statement in bpf_jit_insn(). This leads to the following compile warning: arch/s390/net/bpf_jit_comp.c: In function 'bpf_jit_prog': arch/s390/net/bpf_jit_comp.c:1144:1: warning: frame size of function 'bpf_jit_prog' is 12592 bytes which is more than half the stack size. The dynamic check would not be reliable. No check emitted for this function. arch/s390/net/bpf_jit_comp.c:1144:1: warning: the frame size of 12504 bytes is larger than 1024 bytes [-Wframe-larger-than=] And indead gcc allocates 12592 bytes of stack space: # objdump -d arch/s390/net/bpf_jit_comp.o ... 0000000000000c60 : c60: eb 6f f0 48 00 24 stmg %r6,%r15,72(%r15) c66: b9 04 00 ef lgr %r14,%r15 c6a: e3 f0 fe d0 fc 71 lay %r15,-12592(%r15) As a workaround of that problem we now define bpf_jit_insn() as noinline which then reduces the stack space. # objdump -d arch/s390/net/bpf_jit_comp.o ... 0000000000000070 : 70: eb 6f f0 48 00 24 stmg %r6,%r15,72(%r15) 76: c0 d0 00 00 00 00 larl %r13,76 7c: a7 f1 3f 80 tmll %r15,16256 80: b9 04 00 ef lgr %r14,%r15 84: e3 f0 ff a0 ff 71 lay %r15,-96(%r15) Signed-off-by: Michael Holzheu Signed-off-by: Martin Schwidefsky --- arch/s390/net/bpf_jit_comp.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c index 065aca02bc65..20c146d1251a 100644 --- a/arch/s390/net/bpf_jit_comp.c +++ b/arch/s390/net/bpf_jit_comp.c @@ -443,8 +443,11 @@ static void bpf_jit_epilogue(struct bpf_jit *jit) /* * Compile one eBPF instruction into s390x code + * + * NOTE: Use noinline because for gcov (-fprofile-arcs) gcc allocates a lot of + * stack space for the large switch statement. */ -static int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, int i) +static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, int i) { struct bpf_insn *insn = &fp->insnsi[i]; int jmp_off, last, insn_count = 1; -- 2.20.1