[v3,resend] Fix misaligned accesses to fields in HEADER struct defined in <arpa/nameser_compat.h>
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Build for i686
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Commit Message
This is a resend of the following message:
https://sourceware.org/legacy-ml/libc-alpha/2016-06/msg01020.html
I checked that the attached change still applies to the current
master tree and that it fixes the misaligned accesses on hppa.
This is BZ 20243.
Dave
---
Comments
On Mär 15 2022, John David Anglin wrote:
> diff --git a/resolv/res_mkquery.c b/resolv/res_mkquery.c
> index 5bc5b41531..9b82c82157 100644
> --- a/resolv/res_mkquery.c
> +++ b/resolv/res_mkquery.c
> @@ -193,6 +193,15 @@ context_mkquery_common (struct resolv_context *ctx,
> return result;
> }
>
> +/* 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
> +
The only use of HEADER below that point is in __res_nopt, and AFACS the
only caller __res_context_query always uses aligned memory.
On 2022-03-16 12:15 p.m., Andreas Schwab wrote:
> On Mär 15 2022, John David Anglin wrote:
>
>> diff --git a/resolv/res_mkquery.c b/resolv/res_mkquery.c
>> index 5bc5b41531..9b82c82157 100644
>> --- a/resolv/res_mkquery.c
>> +++ b/resolv/res_mkquery.c
>> @@ -193,6 +193,15 @@ context_mkquery_common (struct resolv_context *ctx,
>> return result;
>> }
>>
>> +/* 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
>> +
> The only use of HEADER below that point is in __res_nopt, and AFACS the
> only caller __res_context_query always uses aligned memory.
Yes, it appears the callers of __res_nopt always use aligned memory. I'll check if this hunk can
be removed.
@@ -193,6 +193,15 @@ context_mkquery_common (struct resolv_context *ctx,
return result;
}
+/* 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
+
/* Form all types of queries. Returns the size of the result or -1 on
error.
@@ -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;
@@ -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