From: John David Anglin <dave.anglin@bell.net>
To: libc-alpha@sourceware.org
Subject: [PATCH v4] Fix misaligned accesses to fields in HEADER struct defined in <arpa/nameser_compat.h>
Date: Thu, 17 Mar 2022 23:04:27 +0000 [thread overview]
Message-ID: <YjO+e+33ZoHL8EbV@mx3210.localdomain> (raw)
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resolv: Fix unaligned accesses to fields in HEADER struct
The structure HEADER is normally aligned to a word boundary but
sometimes it needs to be accessed when aligned on a byte boundary.
This change defines a new typedef, UHEADER, with alignment 1.
It is used to ensure the fields are accessed with byte loads and
stores when necessary.
V4: Change to res_mkquery.c deleted. Small whitespace fix.
Dave
---
diff --git a/resolv/res_query.c b/resolv/res_query.c
index 5d0a68dc81..4ac2c516a1 100644
--- a/resolv/res_query.c
+++ b/resolv/res_query.c
@@ -81,6 +81,14 @@
#include <string.h>
#include <shlib-compat.h>
+/* The structure HEADER is normally aligned to a word boundary and its
+ fields are accessed using word loads and stores. We need to access
+ this structure when it is aligned on a byte boundary. This can cause
+ problems on machines with strict alignment. So, we create a new
+ typedef to reduce its alignment to one. This ensures the fields are
+ accessed with byte loads and stores. */
+typedef HEADER __attribute__ ((__aligned__(1))) UHEADER;
+
#if PACKETSZ > 65536
#define MAXPACKET PACKETSZ
#else
@@ -112,8 +120,8 @@ __res_context_query (struct resolv_context *ctx, const char *name,
int *nanswerp2, int *resplen2, int *answerp2_malloced)
{
struct __res_state *statp = ctx->resp;
- HEADER *hp = (HEADER *) answer;
- HEADER *hp2;
+ UHEADER *hp = (UHEADER *) answer;
+ UHEADER *hp2;
int n, use_malloc = 0;
size_t bufsize = (type == T_QUERY_A_AND_AAAA ? 2 : 1) * QUERYSIZE;
@@ -217,7 +225,7 @@ __res_context_query (struct resolv_context *ctx, const char *name,
if (answerp != NULL)
/* __res_context_send might have reallocated the buffer. */
- hp = (HEADER *) *answerp;
+ hp = (UHEADER *) *answerp;
/* We simplify the following tests by assigning HP to HP2 or
vice versa. It is easy to verify that this is the same as
@@ -228,7 +236,7 @@ __res_context_query (struct resolv_context *ctx, const char *name,
}
else
{
- hp2 = (HEADER *) *answerp2;
+ hp2 = (UHEADER *) *answerp2;
if (n < (int) sizeof (HEADER))
{
hp = hp2;
@@ -338,7 +346,7 @@ __res_context_search (struct resolv_context *ctx,
{
struct __res_state *statp = ctx->resp;
const char *cp;
- HEADER *hp = (HEADER *) answer;
+ UHEADER *hp = (UHEADER *) answer;
char tmp[NS_MAXDNAME];
u_int dots;
int trailing_dot, ret, saved_herrno;
diff --git a/resolv/res_send.c b/resolv/res_send.c
index 5d6be4b82d..24e98f0bfe 100644
--- a/resolv/res_send.c
+++ b/resolv/res_send.c
@@ -111,6 +111,15 @@
#include <libc-diag.h>
#include <random-bits.h>
+/* The structure HEADER is normally aligned to a word boundary and its
+ fields are accessed using word loads and stores. We need to access
+ this structure when it is aligned on a byte boundary. This can cause
+ problems on machines with strict alignment. So, we create a new
+ typedef to reduce its alignment to one. This ensures the fields are
+ accessed with byte loads and stores. */
+typedef HEADER __attribute__ ((__aligned__(1))) UHEADER;
+#define HEADER UHEADER
+
#if PACKETSZ > 65536
#define MAXPACKET PACKETSZ
#else
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next reply other threads:[~2022-03-17 23:04 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-17 23:04 John David Anglin [this message]
2022-03-18 17:37 ` Adhemerval Zanella
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