[DTrace-devel] [PATCH v2] Make DCTX_RODATA available to BPF functions

[eugene.loh at oracle.com]

From: Eugene Loh <eugene.loh at oracle.com>

Use DCTX_RODATA in inet_ntoa.S.

Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
---
 bpf/inet_ntoa6.S     | 12 +++---------
 libdtrace/dt_bpf.h   |  9 +++++----
 libdtrace/dt_cc.c    |  3 +++
 libdtrace/dt_dlibs.c |  1 +
 4 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/bpf/inet_ntoa6.S b/bpf/inet_ntoa6.S
index 24b7232d..d00acbfe 100644
--- a/bpf/inet_ntoa6.S
+++ b/bpf/inet_ntoa6.S
@@ -5,14 +5,6 @@
 
 #define BPF_FUNC_probe_read		4
 
-/*
- * We sadly cannot include struct declarations in assembler input files, so we
- * cannot use offsetof() to programmatically determine the offset of the rodata
- * member in the DTrace context (dt_ctx_t).  If that structure changes, the
- * following define must be updated as well.
- */
-#define DCTX_RODATA			56
-
 #define OUTPUT_LEN			40
 #define INPUT_LEN			16
 
@@ -225,7 +217,9 @@ dt_inet_ntoa6:
 	 * have the code below output the address in two parts: a 7 word
 	 * prefix followed by a 1 word suffix.
 	 */
-	ldxdw	%r6, [%r6 + DCTX_RODATA]
+	lddw	%r1, DCTX_RODATA
+	add	%r1, %r6
+	ldxdw	%r6, [%r1 + 0]
 	ldxw	%r1, [%fp + -4]		/* restore tbloff */
 	lddw	%r0, RODATA_SIZE
 	jge	%r1, %r0, .Ldone
diff --git a/libdtrace/dt_bpf.h b/libdtrace/dt_bpf.h
index bd87869e..0d96fd43 100644
--- a/libdtrace/dt_bpf.h
+++ b/libdtrace/dt_bpf.h
@@ -37,10 +37,11 @@ extern "C" {
 #define DT_CONST_TASK_COMM		16
 #define DT_CONST_MUTEX_OWNER		17
 #define DT_CONST_RWLOCK_CNTS		18
-#define DT_CONST_RODATA_OFF		19
-#define DT_CONST_RODATA_SIZE		20
-#define DT_CONST_ZERO_OFF		21
-#define DT_CONST_STACK_OFF		22
+#define DT_CONST_DCTX_RODATA		19
+#define DT_CONST_RODATA_OFF		20
+#define DT_CONST_RODATA_SIZE		21
+#define DT_CONST_ZERO_OFF		22
+#define DT_CONST_STACK_OFF		23
 
 #define DT_BPF_LOG_SIZE_DEFAULT	(UINT32_MAX >> 8)
 #define DT_BPF_LOG_SIZE_SMALL	4096
diff --git a/libdtrace/dt_cc.c b/libdtrace/dt_cc.c
index b90c42d8..f5632cba 100644
--- a/libdtrace/dt_cc.c
+++ b/libdtrace/dt_cc.c
@@ -1164,6 +1164,9 @@ dt_link_construct(dtrace_hdl_t *dtp, const dt_probe_t *prp, dtrace_difo_t *dp,
 				nrp->dofr_data = total_offset;
 				continue;
 			}
+			case DT_CONST_DCTX_RODATA:
+				nrp->dofr_data = DCTX_RODATA;
+				continue;
 			case DT_CONST_RODATA_OFF:
 				nrp->dofr_data = dtp->dt_rooffset;
 				continue;
diff --git a/libdtrace/dt_dlibs.c b/libdtrace/dt_dlibs.c
index 54d96b89..5d82f30c 100644
--- a/libdtrace/dt_dlibs.c
+++ b/libdtrace/dt_dlibs.c
@@ -91,6 +91,7 @@ static const dt_ident_t		dt_bpf_symbols[] = {
 	DT_BPF_SYMBOL_ID(TASK_COMM, DT_IDENT_SCALAR, DT_CONST_TASK_COMM),
 	DT_BPF_SYMBOL_ID(MUTEX_OWNER, DT_IDENT_SCALAR, DT_CONST_MUTEX_OWNER),
 	DT_BPF_SYMBOL_ID(RWLOCK_CNTS, DT_IDENT_SCALAR, DT_CONST_RWLOCK_CNTS),
+	DT_BPF_SYMBOL_ID(DCTX_RODATA, DT_IDENT_SCALAR, DT_CONST_DCTX_RODATA),
 	DT_BPF_SYMBOL_ID(RODATA_OFF, DT_IDENT_SCALAR, DT_CONST_RODATA_OFF),
 	DT_BPF_SYMBOL_ID(RODATA_SIZE, DT_IDENT_SCALAR, DT_CONST_RODATA_SIZE),
 	DT_BPF_SYMBOL_ID(ZERO_OFF, DT_IDENT_SCALAR, DT_CONST_ZERO_OFF),
-- 
2.18.4