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64-bit alignment in serialised data

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The payload in a struct serdata_default is assumed to be at a 64-bit
offset for conversion to/from a dds_{i,o}stream_t and getting padding
calculations in the serialised representation correct.  The definition
did not guarantee this and got it wrong on a 32-bit release build.

This commit computes the required padding at compile time and at
verifies the assumption holds where it matters.

Signed-off-by: Erik Boasson <eb@ilities.com>
This commit is contained in:
Erik Boasson 2019-07-15 16:45:45 +02:00 • committed by eboasson
parent 2fe4a4ca35
commit 0dd2155f99
2 changed files with 42 additions and 13 deletions
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2
src/core/ddsc/src/dds_stream.c
View file

@ -1614,6 +1614,8 @@ void dds_stream_extract_keyhash (dds_istream_t * __restrict is, dds_keyhash_t *
**
*******************************************************************************************/
DDSRT_STATIC_ASSERT ((offsetof (struct ddsi_serdata_default, data) % 8) == 0);
void dds_istream_from_serdata_default (dds_istream_t * __restrict s, const struct ddsi_serdata_default * __restrict d)
{
s->m_buffer = (const unsigned char *) d;

53
src/core/ddsi/include/dds/ddsi/ddsi_serdata_default.h
View file

@ -49,26 +49,52 @@ typedef struct dds_keyhash {
unsigned m_iskey : 1; /* m_hash is key value */
} dds_keyhash_t;
struct ddsi_serdata_default {
struct ddsi_serdata c;
uint32_t pos;
uint32_t size;
/* Debug builds may want to keep some additional state */
#ifndef NDEBUG
#define DDSI_SERDATA_DEFAULT_DEBUG_FIELDS \
bool fixed;
#else
#define DDSI_SERDATA_DEFAULT_DEBUG_FIELDS
#endif
dds_keyhash_t keyhash;
struct serdatapool *pool;
struct ddsi_serdata_default *next; /* in pool->freelist */
/* There is an alignment requirement on the raw data (it must be at
offset mod 8 for the conversion to/from a dds_stream to work).
So we define two types: one without any additional padding, and
one where the appropriate amount of padding is inserted */
#define DDSI_SERDATA_DEFAULT_PREPAD \
struct ddsi_serdata c; \
uint32_t pos; \
uint32_t size; \
DDSI_SERDATA_DEFAULT_DEBUG_FIELDS \
dds_keyhash_t keyhash; \
struct serdatapool *pool; \
struct ddsi_serdata_default *next /* in pool->freelist */
#define DDSI_SERDATA_DEFAULT_POSTPAD \
struct CDRHeader hdr; \
char data[]
/* padding to ensure CDRHeader is at an offset 4 mod 8 from the
start of the memory, so that data is 8-byte aligned provided
serdata is 8-byte aligned */
char pad[8 - ((sizeof (struct ddsi_serdata) + 4) % 8)];
struct CDRHeader hdr;
char data[];
struct ddsi_serdata_default_unpadded {
DDSI_SERDATA_DEFAULT_PREPAD;
DDSI_SERDATA_DEFAULT_POSTPAD;
};
#ifdef __GNUC__
#define DDSI_SERDATA_DEFAULT_PAD(n) ((n) % 8)
#else
#define DDSI_SERDATA_DEFAULT_PAD(n) (n)
#endif
struct ddsi_serdata_default {
DDSI_SERDATA_DEFAULT_PREPAD;
char pad[DDSI_SERDATA_DEFAULT_PAD (8 - (offsetof (struct ddsi_serdata_default_unpadded, data) % 8))];
DDSI_SERDATA_DEFAULT_POSTPAD;
};
#undef DDSI_SERDATA_DEFAULT_PAD
#undef DDSI_SERDATA_DEFAULT_POSTPAD
#undef DDSI_SERDATA_DEFAULT_PREPAD
#undef DDSI_SERDATA_DEFAULT_FIXED_FIELD
struct dds_key_descriptor;
struct dds_topic_descriptor;
@ -80,6 +106,7 @@ typedef bool (*dds_topic_intern_filter_fn) (const void * sample, void *ctx);
struct ddsi_sertopic_default {
struct ddsi_sertopic c;
uint16_t native_encoding_identifier; /* (PL_)?CDR_(LE|BE) */
struct serdatapool *serpool;
struct dds_topic_descriptor * type;
unsigned nkeys;