[DTrace-devel] [PATCH 07/47] Provide trampoline code for BEGIN, END, and ERROR probes.
Kris Van Hees
kris.van.hees at oracle.com
Sun May 3 20:16:46 PDT 2020
THe 'dtrace' provider implements BEGIN, END, and ERROR probes. The
BEGIN and END probes will be triggered from uprobe events. This
patch provides the trampoline implementation for these probes.
Note that the ERROR probe is one that gets triggered as a result of
errors occuring during the processing of another probe and that one
will be implemented differently - it is not currently available.
Orabug: 31220513
Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
libdtrace/dt_prov_dtrace.c | 165 ++++++++++++++++++++++++++++++++++++-
1 file changed, 164 insertions(+), 1 deletion(-)
diff --git a/libdtrace/dt_prov_dtrace.c b/libdtrace/dt_prov_dtrace.c
index 7cc09b88..b2327dc2 100644
--- a/libdtrace/dt_prov_dtrace.c
+++ b/libdtrace/dt_prov_dtrace.c
@@ -6,8 +6,11 @@
*
* The core probe provider for DTrace for the BEGIN, END, and ERROR probes.
*/
+#include <assert.h>
#include <string.h>
+#include <bpf_asm.h>
+
#include "dt_provider.h"
#include "dt_probe.h"
@@ -38,6 +41,165 @@ static int dtrace_populate(dtrace_hdl_t *dtp)
return n;
}
+/*
+* Generate a BPF trampoline for a dtrace probe (BEGIN, END, or ERROR).
+ *
+ * The trampoline function is called when a dtrace probe triggers, and it must
+ * satisfy the following prototype:
+ *
+ * int dt_dtrace(dt_pt_regs *regs)
+ *
+ * The trampoline will populate a dt_bpf_context struct and then call the
+ * function that implements tha compiled D clause. It returns the value that
+ * it gets back from that function.
+ */
+static void dtrace_trampoline(dt_pcb_t *pcb, int haspred)
+{
+ int i;
+ dt_irlist_t *dlp = &pcb->pcb_ir;
+ struct bpf_insn instr;
+ uint_t lbl_exit = dt_irlist_label(dlp);
+ dt_ident_t *idp;
+
+#define DCTX_FP(off) (-(ushort_t)DCTX_SIZE + (ushort_t)(off))
+
+ /*
+ * int dt_dtrace(dt_pt_regs *regs)
+ * {
+ * struct dt_bpf_context dctx;
+ *
+ * memset(&dctx, 0, sizeof(dctx));
+ *
+ * dctx.epid = EPID;
+ * (we clear dctx.pad and dctx.fault because of the memset above)
+ */
+ idp = dt_dlib_get_var(pcb->pcb_hdl, "EPID");
+ assert(idp != NULL);
+ instr = BPF_STORE_IMM(BPF_W, BPF_REG_FP, DCTX_FP(DCTX_EPID), -1);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ dlp->dl_last->di_extern = idp;
+ instr = BPF_STORE_IMM(BPF_W, BPF_REG_FP, DCTX_FP(DCTX_PAD), 0);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_STORE_IMM(BPF_DW, BPF_REG_FP, DCTX_FP(DCTX_FAULT), 0);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+
+ /*
+ * dctx.regs = *regs;
+ */
+ for (i = 0; i < sizeof(dt_pt_regs); i += 8) {
+ instr = BPF_LOAD(BPF_DW, BPF_REG_0, BPF_REG_1, i);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_STORE(BPF_DW, BPF_REG_FP, DCTX_FP(DCTX_REGS) + i,
+ BPF_REG_0);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ }
+
+ /*
+ * dctx.argv[0] = PT_REGS_PARAM1(regs);
+ * dctx.argv[1] = PT_REGS_PARAM2(regs);
+ * dctx.argv[2] = PT_REGS_PARAM3(regs);
+ * dctx.argv[3] = PT_REGS_PARAM4(regs);
+ * dctx.argv[4] = PT_REGS_PARAM5(regs);
+ * dctx.argv[5] = PT_REGS_PARAM6(regs);
+ */
+ instr = BPF_LOAD(BPF_DW, BPF_REG_0, BPF_REG_1, PT_REGS_ARG0);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_STORE(BPF_DW, BPF_REG_FP, DCTX_FP(DCTX_ARG(0)), BPF_REG_0);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_LOAD(BPF_DW, BPF_REG_0, BPF_REG_1, PT_REGS_ARG1);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_STORE(BPF_DW, BPF_REG_FP, DCTX_FP(DCTX_ARG(1)), BPF_REG_0);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_LOAD(BPF_DW, BPF_REG_0, BPF_REG_1, PT_REGS_ARG2);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_STORE(BPF_DW, BPF_REG_FP, DCTX_FP(DCTX_ARG(2)), BPF_REG_0);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_LOAD(BPF_DW, BPF_REG_0, BPF_REG_1, PT_REGS_ARG3);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_STORE(BPF_DW, BPF_REG_FP, DCTX_FP(DCTX_ARG(3)), BPF_REG_0);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_LOAD(BPF_DW, BPF_REG_0, BPF_REG_1, PT_REGS_ARG4);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_STORE(BPF_DW, BPF_REG_FP, DCTX_FP(DCTX_ARG(4)), BPF_REG_0);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_LOAD(BPF_DW, BPF_REG_0, BPF_REG_1, PT_REGS_ARG5);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_STORE(BPF_DW, BPF_REG_FP, DCTX_FP(DCTX_ARG(5)), BPF_REG_0);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+
+ /*
+ * (we clear dctx.argv[6] and on because of the memset above)
+ */
+ for (i = 6; i < sizeof(((struct dt_bpf_context *)0)->argv) / 8; i++) {
+ instr = BPF_STORE_IMM(BPF_DW, BPF_REG_FP, DCTX_FP(DCTX_ARG(i)),
+ 0);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ }
+
+ /*
+ * We know the BPF context (regs) is in %r1. Since we will be passing
+ * the DTrace context (dctx) as 2nd argument to dt_predicate() (if
+ * there is a predicate) and dt_program, we need it in %r2.
+ */
+ instr = BPF_MOV_REG(BPF_REG_2, BPF_REG_FP);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, DCTX_FP(0));
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+
+ /*
+ * if (haspred) {
+ * rc = dt_predicate(regs, dctx);
+ * if (rc == 0) goto exit;
+ * }
+ */
+ if (haspred) {
+ /*
+ * Save the BPF context (regs) and DTrace context (dctx) in %r6
+ * and %r7 respectively because the BPF verifier will mark %r1
+ * through %r5 unknown after we call dt_predicate (even if we
+ * do not clobber them).
+ */
+ instr = BPF_MOV_REG(BPF_REG_6, BPF_REG_1);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_MOV_REG(BPF_REG_7, BPF_REG_2);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+
+ idp = dt_dlib_get_func(pcb->pcb_hdl, "dt_predicate");
+ assert(idp != NULL);
+ instr = BPF_CALL_FUNC(idp->di_id);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ dlp->dl_last->di_extern = idp;
+ instr = BPF_BRANCH_IMM(BPF_JEQ, BPF_REG_0, 0, lbl_exit);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+
+ /*
+ * Restore BPF context (regs) and DTrace context (dctx) from
+ * %r6 and %r7 into %r1 and %r2 respectively.
+ */
+ instr = BPF_MOV_REG(BPF_REG_1, BPF_REG_6);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ instr = BPF_MOV_REG(BPF_REG_2, BPF_REG_7);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ }
+
+ /*
+ * rc = dt_program(scd, dctx);
+ */
+ idp = dt_dlib_get_func(pcb->pcb_hdl, "dt_program");
+ assert(idp != NULL);
+ instr = BPF_CALL_FUNC(idp->di_id);
+ dt_irlist_append(dlp, dt_cg_node_alloc(DT_LBL_NONE, instr));
+ dlp->dl_last->di_extern = idp;
+
+ /*
+ * exit:
+ * return rc;
+ * }
+ */
+ instr = BPF_RETURN();
+ dt_irlist_append(dlp, dt_cg_node_alloc(lbl_exit, instr));
+}
+
#if 0
#define EVENT_PREFIX "tracepoint/dtrace/"
@@ -78,8 +240,9 @@ static int dtrace_attach(const char *name, int bpf_fd)
dt_provimpl_t dt_dtrace = {
.name = "dtrace",
- .prog_type = BPF_PROG_TYPE_UNSPEC,
+ .prog_type = BPF_PROG_TYPE_KPROBE,
.populate = &dtrace_populate,
+ .trampoline = &dtrace_trampoline,
#if 0
.resolve_event = &dtrace_resolve_event,
.attach = &dtrace_attach,
--
2.26.0
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