[DTrace-devel] [PATCH 7/9] Consolidate bpf_get_stack()-call code generation for stack and ustack()
eugene.loh at oracle.com
eugene.loh at oracle.com
Thu Oct 5 21:14:05 UTC 2023
From: Eugene Loh <eugene.loh at oracle.com>
Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
---
libdtrace/dt_cg.c | 141 ++++++++++++++++++++++++++++------------------
1 file changed, 85 insertions(+), 56 deletions(-)
diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
index 6cae8814..ba698d2f 100644
--- a/libdtrace/dt_cg.c
+++ b/libdtrace/dt_cg.c
@@ -2225,33 +2225,90 @@ dt_cg_ustack_arg(dtrace_hdl_t *dtp, dt_node_t *dnp)
return DTRACE_USTACK_ARG(nframes, strsize);
}
-static void
-dt_cg_act_stack(dt_pcb_t *pcb, dt_node_t *dnp, dtrace_actkind_t kind)
+/*
+ * Call the bpf_get_stack() helper function.
+ *
+ * dnp->dn_arg has optional, integer-constant sizing information.
+ *
+ * If reg>=0, reg is a register holding the output pointer.
+ * If reg<0, we write the stack to the output buffer in %r9.
+ *
+ * These cases treat "off" differently:
+ * - reg>=0: "off" tracks how far the pointer in "reg" has
+ * been advanced, both at function entry and return
+ *
+ * - reg<0: "off" is basically just a local variable since
+ * offsets with the %r9 buffer are managed by
+ * dt_rec_add()
+ *
+ * The "user" flag indicates whether a user (or kernel) stack is desired.
+ */
+static int
+dt_cg_act_stack_sub(dt_pcb_t *pcb, dt_node_t *dnp, int reg, int off, int user)
{
dtrace_hdl_t *dtp = pcb->pcb_hdl;
dt_irlist_t *dlp = &pcb->pcb_ir;
dt_regset_t *drp = pcb->pcb_regs;
- int nframes;
- int skip = 0;
- uint_t off;
+ uint64_t arg;
+ int nframes, stacksize, prefsz, align = sizeof(uint64_t);
uint_t lbl_valid = dt_irlist_label(dlp);
- nframes = dt_cg_stack_nframes(dtp, dnp);
+ /* Get sizing information from dnp->dn_arg. */
+ if (user) {
+ arg = dt_cg_ustack_arg(dtp, dnp);
+ nframes = DTRACE_USTACK_NFRAMES(arg);
+ prefsz = sizeof(uint64_t);
+ } else {
+ nframes = dt_cg_stack_nframes(dtp, dnp);
+ arg = nframes;
+ prefsz = 0;
+ }
+ stacksize = nframes * sizeof(uint64_t);
+
+ /* Handle alignment and reserve space in the output buffer. */
+ if (reg >= 0) {
+ uint_t nextoff;
+ nextoff = (off + (align - 1)) & ~(align - 1);
+ if (off < nextoff)
+ emit(dlp, BPF_ALU64_IMM(BPF_ADD, reg, nextoff - off));
+ off = nextoff + prefsz + stacksize;
+ } else {
+ off = dt_rec_add(dtp, dt_cg_fill_gap,
+ user ? DTRACEACT_USTACK : DTRACEACT_STACK,
+ prefsz + stacksize, align, NULL, arg);
+ }
- /* Reserve space in the output buffer. */
- off = dt_rec_add(dtp, dt_cg_fill_gap, DTRACEACT_STACK,
- sizeof(uint64_t) * nframes, sizeof(uint64_t),
- NULL, nframes);
+ /* Write the tgid. */
+ if (user) {
+ if (dt_regset_xalloc_args(drp) == -1)
+ longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
+ dt_regset_xalloc(drp, BPF_REG_0);
+ emit(dlp, BPF_CALL_HELPER(BPF_FUNC_get_current_pid_tgid));
+ dt_regset_free_args(drp);
+ emit(dlp, BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xffffffff));
+ if (reg >= 0)
+ emit(dlp, BPF_STORE(BPF_DW, reg, 0, BPF_REG_0));
+ else
+ emit(dlp, BPF_STORE(BPF_DW, BPF_REG_9, off, BPF_REG_0));
+ dt_regset_free(drp, BPF_REG_0);
+ }
- /* Now call bpf_get_stack(ctx, buf, size, flags). */
+ /* Call bpf_get_stack(ctx, buf, size, flags). */
if (dt_regset_xalloc_args(drp) == -1)
longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
emit(dlp, BPF_LOAD(BPF_DW, BPF_REG_1, BPF_REG_FP, DT_STK_DCTX));
emit(dlp, BPF_LOAD(BPF_DW, BPF_REG_1, BPF_REG_1, DCTX_CTX));
- emit(dlp, BPF_MOV_REG(BPF_REG_2, BPF_REG_9));
- emit(dlp, BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, off));
- emit(dlp, BPF_MOV_IMM(BPF_REG_3, sizeof(uint64_t) * nframes));
- emit(dlp, BPF_MOV_IMM(BPF_REG_4, skip & BPF_F_SKIP_FIELD_MASK));
+ if (reg >= 0) {
+ emit(dlp, BPF_MOV_REG(BPF_REG_2, reg));
+ if (prefsz)
+ emit(dlp, BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, prefsz));
+ } else {
+ emit(dlp, BPF_MOV_REG(BPF_REG_2, BPF_REG_9));
+ emit(dlp, BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, off + prefsz));
+ }
+ emit(dlp, BPF_MOV_IMM(BPF_REG_3, stacksize));
+ emit(dlp, BPF_MOV_IMM(BPF_REG_4, (0 & BPF_F_SKIP_FIELD_MASK)
+ | (user ? BPF_F_USER_STACK : 0)));
dt_regset_xalloc(drp, BPF_REG_0);
emit(dlp, BPF_CALL_HELPER(BPF_FUNC_get_stack));
dt_regset_free_args(drp);
@@ -2260,6 +2317,18 @@ dt_cg_act_stack(dt_pcb_t *pcb, dt_node_t *dnp, dtrace_actkind_t kind)
dt_cg_probe_error(pcb, DTRACEFLT_BADSTACK, DT_ISIMM, 0);
emitl(dlp, lbl_valid,
BPF_NOP());
+
+ /* Finish. */
+ if (reg >= 0)
+ emit(dlp, BPF_ALU64_IMM(BPF_ADD, reg, prefsz + stacksize));
+
+ return off;
+}
+
+static void
+dt_cg_act_stack(dt_pcb_t *pcb, dt_node_t *dnp, dtrace_actkind_t kind)
+{
+ dt_cg_act_stack_sub(pcb, dnp, -1, 0, 0);
}
static void
@@ -2417,47 +2486,7 @@ dt_cg_act_trunc(dt_pcb_t *pcb, dt_node_t *dnp, dtrace_actkind_t kind)
static void
dt_cg_act_ustack(dt_pcb_t *pcb, dt_node_t *dnp, dtrace_actkind_t kind)
{
- dt_irlist_t *dlp = &pcb->pcb_ir;
- dt_regset_t *drp = pcb->pcb_regs;
- dtrace_hdl_t *dtp = pcb->pcb_hdl;
- uint64_t arg;
- int nframes, stacksize;
- int skip = 0;
- uint_t off;
- uint_t lbl_valid = dt_irlist_label(dlp);
-
- arg = dt_cg_ustack_arg(dtp, dnp);
- nframes = DTRACE_USTACK_NFRAMES(arg);
- stacksize = nframes * sizeof(uint64_t);
-
- /* Reserve space in the output buffer. */
- off = dt_rec_add(pcb->pcb_hdl, dt_cg_fill_gap, DTRACEACT_USTACK,
- 8 + stacksize, 8, NULL, arg);
-
- if (dt_regset_xalloc_args(drp) == -1)
- longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
- dt_regset_xalloc(drp, BPF_REG_0);
-
- /* Write the tgid. */
- emit(dlp, BPF_CALL_HELPER(BPF_FUNC_get_current_pid_tgid));
- emit(dlp, BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xffffffff));
- emit(dlp, BPF_STORE(BPF_DW, BPF_REG_9, off, BPF_REG_0));
-
- /* Now call bpf_get_stack(ctx, buf, size, flags). */
- emit(dlp, BPF_LOAD(BPF_DW, BPF_REG_1, BPF_REG_FP, DT_STK_DCTX));
- emit(dlp, BPF_LOAD(BPF_DW, BPF_REG_1, BPF_REG_1, DCTX_CTX));
- emit(dlp, BPF_MOV_REG(BPF_REG_2, BPF_REG_9));
- emit(dlp, BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, off + 8));
- emit(dlp, BPF_MOV_IMM(BPF_REG_3, stacksize));
- emit(dlp, BPF_MOV_IMM(BPF_REG_4, (skip & BPF_F_SKIP_FIELD_MASK)
- | BPF_F_USER_STACK));
- emit(dlp, BPF_CALL_HELPER(BPF_FUNC_get_stack));
- dt_regset_free_args(drp);
- emit(dlp, BPF_BRANCH_IMM(BPF_JSGE, BPF_REG_0, 0, lbl_valid));
- dt_regset_free(drp, BPF_REG_0);
- dt_cg_probe_error(pcb, DTRACEFLT_BADSTACK, DT_ISIMM, 0);
- emitl(dlp, lbl_valid,
- BPF_NOP());
+ dt_cg_act_stack_sub(pcb, dnp, -1, 0, 1);
}
typedef void dt_cg_action_f(dt_pcb_t *, dt_node_t *, dtrace_actkind_t);
--
2.18.4
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