SIGSEGV fills si_addr only for memory access faults.  Add a note to clarify.

Signed-off-by: Yu-cheng Yu <redacted>
Cc: Alejandro Colomar <redacted>
Cc: Michael Kerrisk <redacted>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Florian Weimer <redacted>
Cc: "H.J. Lu" <redacted>
Cc: linux-kernel@vger.kernel.org
Cc: linux-api@vger.kenel.org
Link: https://lore.kernel.org/linux-api/20210217222730.15819-7-yu-cheng.yu@intel.com/ (local)
---
 man2/sigaction.2 | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/man2/sigaction.2 b/man2/sigaction.2
index 49a30f11e..bea884a23 100644
--- a/man2/sigaction.2
+++ b/man2/sigaction.2

@@ -467,7 +467,7 @@ and
 .BR SIGTRAP
 fill in
 .I si_addr
-with the address of the fault.
+with the address of the fault (see notes).
 On some architectures,
 these signals also fill in the
 .I si_trapno

@@ -955,6 +955,11 @@ It is not possible to block
 .IR sa_mask ).
 Attempts to do so are silently ignored.
 .PP
+In a
+.B SIGSEGV,
+if the fault is a memory access fault, si_addr is filled with the address
+causing the fault, otherwise it is not filled.