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authorMichael Holzheu <holzheu@linux.vnet.ibm.com>2015-04-29 18:45:03 +0200
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2015-04-30 13:50:36 +0200
commitb9b4b1cef156e6b403b26ea4cb6d0caf4850e05c (patch)
parent8cc2af7c530e320db442e6efec8c84c125c07c81 (diff)
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 <bpf_jit_prog>: 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 <bpf_jit_insn>: 70: eb 6f f0 48 00 24 stmg %r6,%r15,72(%r15) 76: c0 d0 00 00 00 00 larl %r13,76 <bpf_jit_insn+0x6> 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 <holzheu@linux.vnet.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
1 files changed, 4 insertions, 1 deletions
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;

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