[DTrace-devel] [PATCH v3] Implement the ppid builtin D variable
Kris Van Hees
kris.van.hees at oracle.com
Sat Sep 19 20:43:20 PDT 2020
On Thu, Sep 17, 2020 at 04:14:34PM -0400, eugene.loh at oracle.com wrote:
> From: Eugene Loh <eugene.loh at oracle.com>
>
> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
Reviewed-by: Kris Van Hees <kris.van.hees at oracle.com>
> ---
> bpf/get_bvar.c | 36 ++++++++++++++++++++++++
> libdtrace/dt_bpf.c | 26 +++++++++++++++++
> libdtrace/dt_state.h | 5 ++++
> test/unittest/variables/bvar/tst.ppid.d | 1 -
> test/unittest/variables/bvar/tst.ppid2.d | 20 +++++++++++++
> 5 files changed, 87 insertions(+), 1 deletion(-)
> create mode 100644 test/unittest/variables/bvar/tst.ppid2.d
>
> diff --git a/bpf/get_bvar.c b/bpf/get_bvar.c
> index 0cac46d5..8d595efb 100644
> --- a/bpf/get_bvar.c
> +++ b/bpf/get_bvar.c
> @@ -9,12 +9,14 @@
> #include <dtrace/conf.h>
> #include <dtrace/dif_defines.h>
> #include <dt_dctx.h>
> +#include <dt_state.h>
>
> #ifndef noinline
> # define noinline __attribute__((noinline))
> #endif
>
> extern struct bpf_map_def cpuinfo;
> +extern struct bpf_map_def state;
>
> noinline uint64_t dt_get_bvar(dt_mstate_t *mst, uint32_t id)
> {
> @@ -47,6 +49,40 @@ noinline uint64_t dt_get_bvar(dt_mstate_t *mst, uint32_t id)
>
> return val & 0x00000000ffffffffUL;
> }
> + case DIF_VAR_PPID: {
> + uint64_t ptr;
> + int32_t val = -1;
> + uint32_t key;
> + uint32_t *parent_off;
> + uint32_t *tgid_off;
> +
> + /*
> + * In the "state" map, look up the "struct task_struct" offsets
> + * of real_parent and tgid.
> + */
> + key = DT_STATE_TASK_PARENT_OFF;
> + parent_off = bpf_map_lookup_elem(&state, &key);
> + if (parent_off == NULL)
> + return -1;
> +
> + key = DT_STATE_TASK_TGID_OFF;
> + tgid_off = bpf_map_lookup_elem(&state, &key);
> + if (tgid_off == NULL)
> + return -1;
> +
> + /* Chase pointers val = current->real_parent->tgid. */
> + ptr = bpf_get_current_task();
> + if (ptr == 0)
> + return -1;
> + if (bpf_probe_read((void *) &ptr, 8,
> + (const void *) (ptr + *parent_off)))
> + return -1;
> + if (bpf_probe_read((void *) &val, 4,
> + (const void *) (ptr + *tgid_off)))
> + return -1;
> +
> + return (uint64_t) val;
> + }
> case DIF_VAR_UID: {
> uint64_t val = bpf_get_current_uid_gid();
>
> diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
> index 4e0cdc91..736b3318 100644
> --- a/libdtrace/dt_bpf.c
> +++ b/libdtrace/dt_bpf.c
> @@ -115,6 +115,28 @@ create_gmap(dtrace_hdl_t *dtp, const char *name, enum bpf_map_type type,
> return fd;
> }
>
> +static int
> +set_task_offsets(dtrace_hdl_t *dtp)
> +{
> + ctf_id_t type;
> + ctf_membinfo_t ctm;
> + ctf_file_t *cfp = dtp->dt_shared_ctf;
> +
> + type = ctf_lookup_by_name(cfp, "struct task_struct");
> + if (type == CTF_ERR)
> + return -1;
> +
> + if (ctf_member_info(cfp, type, "real_parent", &ctm) == CTF_ERR)
> + return -1;
> + dt_state_set_offparent(dtp, ctm.ctm_offset / NBBY);
> +
> + if (ctf_member_info(cfp, type, "tgid", &ctm) == CTF_ERR)
> + return -1;
> + dt_state_set_offtgid(dtp, ctm.ctm_offset / NBBY);
> +
> + return 0;
> +}
> +
> /*
> * Create the global BPF maps that are shared between all BPF programs in a
> * single tracing session:
> @@ -225,6 +247,10 @@ dt_bpf_gmap_create(dtrace_hdl_t *dtp)
> /* Populate the 'cpuinfo' map. */
> dt_bpf_map_update(ci_mapfd, &key, dtp->dt_conf.cpus);
>
> + /* Set some task_struct offsets in state. */
> + if (set_task_offsets(dtp))
> + return dt_set_errno(dtp, EDT_CTF);
> +
> return 0;
> }
>
> diff --git a/libdtrace/dt_state.h b/libdtrace/dt_state.h
> index c6500dca..ed6f2030 100644
> --- a/libdtrace/dt_state.h
> +++ b/libdtrace/dt_state.h
> @@ -21,6 +21,8 @@ typedef enum dt_state_elem {
> DT_STATE_ACTIVITY = 0, /* activity state of the session */
> DT_STATE_BEGANON, /* cpu BEGIN probe executed on */
> DT_STATE_ENDEDON, /* cpu END probe executed on */
> + DT_STATE_TASK_PARENT_OFF, /* offsetof(struct task_struct, real_parent) */
> + DT_STATE_TASK_TGID_OFF, /* offsetof(struct task_struct, tgid) */
> DT_STATE_NUM_ELEMS
> } dt_state_elem_t;
>
> @@ -61,6 +63,9 @@ dt_state_set(dtrace_hdl_t *dtp, uint32_t key, uint32_t val)
>
> # define dt_state_get_beganon(dtp) dt_state_get(dtp, DT_STATE_BEGANON)
> # define dt_state_get_endedon(dtp) dt_state_get(dtp, DT_STATE_ENDEDON)
> +
> +# define dt_state_set_offparent(dtp, x) dt_state_set(dtp, DT_STATE_TASK_PARENT_OFF, (x))
> +# define dt_state_set_offtgid(dtp, x) dt_state_set(dtp, DT_STATE_TASK_TGID_OFF, (x))
> #endif
>
> #endif /* _DT_STATE_H */
> diff --git a/test/unittest/variables/bvar/tst.ppid.d b/test/unittest/variables/bvar/tst.ppid.d
> index e406b36f..87bc52da 100644
> --- a/test/unittest/variables/bvar/tst.ppid.d
> +++ b/test/unittest/variables/bvar/tst.ppid.d
> @@ -4,7 +4,6 @@
> * Licensed under the Universal Permissive License v 1.0 as shown at
> * http://oss.oracle.com/licenses/upl.
> */
> -/* @@xfail: dtv2 */
>
> /*
> * ASSERTION: The 'ppid' variable can be accessed and is not -1.
> diff --git a/test/unittest/variables/bvar/tst.ppid2.d b/test/unittest/variables/bvar/tst.ppid2.d
> new file mode 100644
> index 00000000..7a50ac89
> --- /dev/null
> +++ b/test/unittest/variables/bvar/tst.ppid2.d
> @@ -0,0 +1,20 @@
> +/*
> + * Oracle Linux DTrace.
> + * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
> + * Licensed under the Universal Permissive License v 1.0 as shown at
> + * http://oss.oracle.com/licenses/upl.
> + */
> +
> +/*
> + * ASSERTION: The 'ppid' variable matches the scripting variable for BEGIN.
> + *
> + * SECTION: Variables/Built-in Variables/ppid
> + */
> +
> +#pragma D option quiet
> +
> +BEGIN {
> + trace(ppid);
> + trace($ppid);
> + exit(ppid == $ppid ? 0 : 1);
> +}
> --
> 2.18.4
>
>
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