Clarify what abort_on_misalignment() does.

It doesn't request byte misalignment repair, it requests that byte
misalignment kill the program with SIGBUS; on platforms that don't
support aligned loads, we should be fetching possibly-misaligned data
using some safe instruction sequence, not by doing misaligned loads and
relying on them to trap to the kernel and be (slowly) emulated.

1 files changed, 9 insertions, 0 deletions

diff --git a/machdep.c b/machdep.c
index 3b8c9664..7b259ae1 100644
--- a/machdep.c
+++ b/machdep.c
@@ -50,6 +50,15 @@ int snprintf(char *, size_t, const char *, ...)
 
 #include "machdep.h"
 
+/*
+ * On platforms where the CPU doesn't support unaligned loads, force
+ * unaligned accesses to abort with SIGBUS, rather than being fixed
+ * up (slowly) by the OS kernel; on those platforms, misaligned accesses
+ * are bugs, and we want tcpdump to crash so that the bugs are reported.
+ *
+ * The only OS on which this is necessary is DEC OSF/1^W^WDigital
+ * UNIX^W^WTru64 UNIX.
+ */
 int
 abort_on_misalignment(char *ebuf _U_, size_t ebufsiz _U_)
 {