[DTrace-devel] [PATCH] Fix stack layout definitions to match the new dt_dctx design
Kris Van Hees
kris.van.hees at oracle.com
Thu Aug 27 11:53:44 PDT 2020
The stack layout was changed with the move of the DTrace machine state
out of the stack. The changes were not properly reflected everywhere,
both in comments and in code:
- dt_cg.c: dt_cg_tramp_prologue()
The comment describing the BPF code to pass the 2nd argument to the
bpf_map_lookup_elem() helper was referring to the wrong stack offset
constant.
The pseudo-code in the comment also incorrectly passed 'mem' rather
than '&mem'.
- dt_dctx.h:
The definition of DCTX_SIZE now explicitly casts to int16_t to
avoid compilation warnings in code that uses it in BPF instructions.
The definition of DCTX_FP(off) is now based on DT_STK_DCTX as the
base offset of the dt_dctx struct (defined in dt_impl.h).
- dt_impl.h:
The comment block describing the stack layout now reflects the
correct layout in view of dt_dctx.
The definitions of DT_STK_BASE and DT_STK_SLOT_SZ now explicitly
cast to int16_t to avoid compilation warnings in code that uses
them in BPF instructions.
The definition of DT_STK_DCTX has been corrected based on its
actual size (DCTX_SIZE).
- tst.stack_layout.r:
Updated the expected output.
Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
libdtrace/dt_cg.c | 4 ++--
libdtrace/dt_dctx.h | 4 ++--
libdtrace/dt_impl.h | 20 ++++++++---------
test/unittest/codegen/tst.stack_layout.r | 28 ++++++++++++------------
4 files changed, 28 insertions(+), 28 deletions(-)
diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
index 0d3463c1..8a7a09db 100644
--- a/libdtrace/dt_cg.c
+++ b/libdtrace/dt_cg.c
@@ -64,10 +64,10 @@ dt_cg_tramp_prologue(dt_pcb_t *pcb, uint_t lbl_exit)
/*
* key = 0; // stw [%fp + DCTX_FP(DCTX_MST)], 0
- * rc = bpf_map_lookup_elem(mem, &key);
+ * rc = bpf_map_lookup_elem(&mem, &key);
* // lddw %r1, &mem
* // mov %r2, %fp
- * // add %r2, DT_STK_LVA_BASE
+ * // add %r2, DCTX_FP(DCTX_MST)
* // call bpf_map_lookup_elem
* // (%r1 ... %r5 clobbered)
* // (%r0 = 'mem' BPF map value)
diff --git a/libdtrace/dt_dctx.h b/libdtrace/dt_dctx.h
index 79ef7105..b315f522 100644
--- a/libdtrace/dt_dctx.h
+++ b/libdtrace/dt_dctx.h
@@ -36,13 +36,13 @@ typedef struct dt_dctx {
#define DCTX_CTX offsetof(dt_dctx_t, ctx)
#define DCTX_MST offsetof(dt_dctx_t, mst)
#define DCTX_BUF offsetof(dt_dctx_t, buf)
-#define DCTX_SIZE sizeof(dt_dctx_t)
+#define DCTX_SIZE (int16_t)sizeof(dt_dctx_t)
/*
* Macro to determine the (negative) offset from the frame pointer (%fp) for
* the given offset in dt_dctx_t.
*/
-#define DCTX_FP(off) (-(ushort_t)DCTX_SIZE + (ushort_t)(off))
+#define DCTX_FP(off) (DT_STK_DCTX + (int16_t)(off))
#define DMST_EPID offsetof(dt_mstate_t, epid)
#define DMST_TAG offsetof(dt_mstate_t, tag)
diff --git a/libdtrace/dt_impl.h b/libdtrace/dt_impl.h
index fb06032d..0f79b45f 100644
--- a/libdtrace/dt_impl.h
+++ b/libdtrace/dt_impl.h
@@ -494,29 +494,29 @@ struct dtrace_hdl {
* +----------------+
* SCRATCH_BASE = -512 | Scratch Memory |
* +----------------+
- * LVAR_END = LVAR(n) = -256 | LVAR n | (n = DT_VAR_LOCAL_MAX = 20)
+ * LVAR_END = LVAR(n) = -256 | LVAR n | (n = DT_VAR_LOCAL_MAX = 19)
* +----------------+
* | ... |
* +----------------+
- * LVAR(1) = -96 | LVAR 1 |
+ * LVAR(1) = -112 | LVAR 1 |
* +----------------+
- * LVAR_BASE = LVAR(0) = -88 | LVAR 0 |
+ * LVAR_BASE = LVAR(0) = -104 | LVAR 0 |
* +----------------+
- * SPILL(n) = -80 | %r8 | (n = DT_STK_NREGS - 1 = 8)
+ * SPILL(n) = -96 | %r8 | (n = DT_STK_NREGS - 1 = 8)
* +----------------+
* | ... |
* +----------------+
- * SPILL(1) = -24 | %r1 |
+ * SPILL(1) = -40 | %r1 |
* +----------------+
- * SPILL_BASE = SPILL(0) = -16 | %r0 |
+ * SPILL_BASE = SPILL(0) = -32 | %r0 |
* +----------------+
- * DCTX = -8 | DTrace Context | -1
+ * DCTX = -24 | DTrace Context | -1
* +----------------+
*/
-#define DT_STK_BASE (0)
-#define DT_STK_SLOT_SZ ((int)sizeof(uint64_t))
+#define DT_STK_BASE ((int16_t)0)
+#define DT_STK_SLOT_SZ ((int16_t)sizeof(uint64_t))
-#define DT_STK_DCTX (DT_STK_BASE - DT_STK_SLOT_SZ)
+#define DT_STK_DCTX (DT_STK_BASE - DCTX_SIZE)
#define DT_STK_SPILL_BASE (DT_STK_DCTX - DT_STK_SLOT_SZ)
#define DT_STK_SPILL(n) (DT_STK_SPILL_BASE - (n) * DT_STK_SLOT_SZ)
#define DT_STK_LVAR_BASE (DT_STK_SPILL(DT_STK_NREGS - 1) - \
diff --git a/test/unittest/codegen/tst.stack_layout.r b/test/unittest/codegen/tst.stack_layout.r
index d0081e53..2155e785 100644
--- a/test/unittest/codegen/tst.stack_layout.r
+++ b/test/unittest/codegen/tst.stack_layout.r
@@ -1,17 +1,17 @@
Base: 0
-dctx: -8
-%r0: -16
-%r1: -24
-%r2: -32
-%r3: -40
-%r4: -48
-%r5: -56
-%r6: -64
-%r7: -72
-%r8: -80
-lvar[ -1]: -87 (ID -1)
-lvar[ 0]: -88 (ID 0)
-lvar[ 1]: -96 (ID 1)
-lvar[ 21]: -256 (ID 21)
+dctx: -24
+%r0: -32
+%r1: -40
+%r2: -48
+%r3: -56
+%r4: -64
+%r5: -72
+%r6: -80
+%r7: -88
+%r8: -96
+lvar[ -1]: -103 (ID -1)
+lvar[ 0]: -104 (ID 0)
+lvar[ 1]: -112 (ID 1)
+lvar[ 19]: -256 (ID 19)
lvar[ -1]: -257 (ID -1)
scratch: -257 .. -512
--
2.28.0
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