[DTrace-devel] [PATCH] Preface usym/umod/uaddr with pid

[eugene.loh at oracle.com]

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

Translation of user space addresses requires that we know which process
to use for the translation.  We have been prefacing the address to
translate like this:
        /* Preface the value with the user process tgid. */
        emit(dlp, BPF_CALL_HELPER(BPF_FUNC_get_current_pid_tgid));
        emit(dlp, BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xffffffff));

One problem is that the IMM "and" operation is a no-op.  The 0xffffffff
is promoted to a 64-bit -1, leading to no %r0 bits changing.  Another
problem is that we are pulling out the tgid.  This means that the
translation will fail.  Further, even if the consumer knew which part
of the pid_tgid combination to use for address translation, keys for
aggregations could fail spuriously due to different tgids for the same
process.

Convert to
        /* Preface the value with the user process pid. */
        emit(dlp, BPF_CALL_HELPER(BPF_FUNC_get_current_pid_tgid));
        emit(dlp, BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, 32));

Also, in the umod test (which uncovered this problem), add ld-*.so to
the list of shared objects we're going to skip.

Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
---
 libdtrace/dt_cg.c                   | 8 ++++----
 test/unittest/profile-n/tst.umod.sh | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
index 461a68270..b07aaea3d 100644
--- a/libdtrace/dt_cg.c
+++ b/libdtrace/dt_cg.c
@@ -1647,13 +1647,13 @@ dt_cg_store_val(dt_pcb_t *pcb, dt_node_t *dnp, dtrace_actkind_t kind,
 	    kind == DTRACEACT_UADDR) {
 		off = dt_rec_add(dtp, dt_cg_fill_gap, kind, 16, 8, NULL, arg);
 
-		/* preface the value with the user process tgid */
+		/* preface the value with the user process pid */
 		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));
+		emit(dlp, BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, 32));
 		emit(dlp, BPF_STORE(BPF_DW, BPF_REG_9, off, BPF_REG_0));
 		dt_regset_free(drp, BPF_REG_0);
 
@@ -3823,13 +3823,13 @@ empty_args:
 				if (tuplesize < nextoff)
 					emit(dlp,  BPF_ALU64_IMM(BPF_ADD, treg, nextoff - tuplesize));
 
-				/* Preface the value with the user process tgid. */
+				/* Preface the value with the user process pid. */
 				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));
+				emit(dlp, BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, 32));
 				emit(dlp, BPF_STORE(BPF_DW, treg, 0, BPF_REG_0));
 				dt_regset_free(drp, BPF_REG_0);
 
diff --git a/test/unittest/profile-n/tst.umod.sh b/test/unittest/profile-n/tst.umod.sh
index a5b1127ff..45d2b1e9b 100755
--- a/test/unittest/profile-n/tst.umod.sh
+++ b/test/unittest/profile-n/tst.umod.sh
@@ -53,7 +53,7 @@ if ! grep -wq 'bash' $tmpfile; then
 fi
 
 # Check that modules are unique.  (Exclude shared libraries and unresolved addresses.)
-if gawk '!/^ *lib/ && !/^ *0x/ {print $1}' $tmpfile | sort | uniq -c | grep -qv " 1 "; then
+if gawk '!/^ *lib/ && !/^ *ld-.*\.so / && !/^ *0x/ {print $1}' $tmpfile | sort | uniq -c | grep -qv " 1 "; then
 	echo ERROR: duplicate umod
 	status=1
 fi
-- 
2.43.5