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If they are left there, then I would argue that we should also include them in the stackdepth count. On Tue, Jun 04, 2024 at 02:00:02PM -0400, eugene.loh--- via DTrace-devel wrote: > From: Eugene Loh > > The return value from the BPF helper function bpf_get_stack() > basically returns the size of the stack returned. We use this > value to report stack depth. > > Some of the top frames can be NULL, however, leading to some > inconsistencies between reported stacks and stack depths. > > Add some code to reduce the stack depth if one or two top > frames are NULL. > > There is an existing test to check for this problem. It will > appear in a later patch since it has multiple problems. > > Signed-off-by: Eugene Loh > --- > bpf/get_bvar.c | 17 +++++++++++++++-- > 1 file changed, 15 insertions(+), 2 deletions(-) > > diff --git a/bpf/get_bvar.c b/bpf/get_bvar.c > index ea5dc6b1..a0c04f3a 100644 > --- a/bpf/get_bvar.c > +++ b/bpf/get_bvar.c > @@ -67,7 +67,9 @@ noinline uint64_t dt_get_bvar(const dt_dctx_t *dctx, uint32_t id, uint32_t idx) > uint32_t bufsiz = (uint32_t) (uint64_t) (&STKSIZ); > uint64_t flags; > char *buf = dctx->mem + (uint64_t)(&STACK_OFF); > - uint64_t stacksize; > + int64_t stacksize; > + int64_t topslot; > + uint64_t *pcs = (uint64_t *)buf; > > if (id == DIF_VAR_USTACKDEPTH) > flags = BPF_F_USER_STACK; > @@ -87,8 +89,19 @@ noinline uint64_t dt_get_bvar(const dt_dctx_t *dctx, uint32_t id, uint32_t idx) > * what we can retrieve. But it's also possible that the > * buffer was exactly large enough. So, leave it to the user > * to interpret the result. > + * > + * The helper function also sometimes returns some empty frames > + * at the top. Bump the depth down some so that the stack depth > + * we report is consistent with the number of frames returned. > + * Arguably, this should be fixed in the kernel, but we can > + * work around the problem for now. > */ > - return stacksize / sizeof(uint64_t); > + topslot = stacksize / sizeof(uint64_t) - 1; > + if (topslot >= 0 && topslot < (bufsiz / sizeof(uint64_t)) && pcs[topslot] == 0) > + topslot--; > + if (topslot >= 0 && topslot < (bufsiz / sizeof(uint64_t)) && pcs[topslot] == 0) > + topslot--; > + return topslot + 1; > } > case DIF_VAR_CALLER: > case DIF_VAR_UCALLER: { > -- > 2.18.4 > > > _______________________________________________ > DTrace-devel mailing list > DTrace-devel@oss.oracle.com > https://oss.oracle.com/mailman/listinfo/dtrace-devel