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spice-common/common/mem.h
Christophe de Dinechin 858a0bfae9 Avoid clang warnings on casts with stricter alignment requirements 
For example, something like this:
    uint8_t  *p8;
    uint32_t *p32 = (uint32_t *) p8;

generates a warning like this:
  spice-channel.c:1350:10: error: cast from 'uint8_t *' (aka 'unsigned char *') to
      'uint32_t *' (aka 'unsigned int *') increases required alignment from 1 to
      4 [-Werror,-Wcast-align]

The warning indicates that we end up with a pointer to data that
should be 4-byte aligned, but its value may be misaligned. On x86,
this does not make much of a difference, except a relatively minor
performance penalty. However, on platforms such as older ARM, misaligned
accesses are emulated by the kernel, and support for them is optional.
So we may end up with a fault.

The intent of the fix here is to make it easy to identify and rework
places where actual mis-alignment occurs. Wherever casts raise the warning,
they are replaced with a macro:

- SPICE_ALIGNED_CAST(type, value) casts value to type, and indicates that
  we believe the resulting pointer is aligned. If it is not, a runtime
  warning will be issued. This check is disabled unless
  --enable-alignment-checks is passed at configure time

- SPICE_UNALIGNED_CAST(type, value) casts value to type, and indicates that
  we believe the resulting pointer is not always aligned.

Any code using SPICE_UNALIGNED_CAST may need to be revisited in order
to improve performance, e.g. by using memcpy.

There are normally no warnings for SPICE_UNALIGNED_CAST, but it is possible
to emit debug messages for mis-alignment in SPICE_UNALIGNED_CAST
by configuring with CFLAGS=-DSPICE_DEBUG_ALIGNMENT.

Signed-off-by: Christophe de Dinechin <dinechin@redhat.com>
2017-06-20 11:33:45 +02:00

200 lines
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/* -*- Mode: C; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/*
Copyright (C) 2010 Red Hat, Inc.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/
#ifndef _H_MEM
#define _H_MEM
#include "log.h"
#include <stdlib.h>
#include <spice/macros.h>
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
SPICE_BEGIN_DECLS
#ifdef STDC_HEADERS
# include <stdlib.h>
# include <stddef.h>
#else
# ifdef HAVE_STDLIB_H
# include <stdlib.h>
# endif
#endif
#ifdef HAVE_ALLOCA_H
# include <alloca.h>
#elif defined __GNUC__
#if !defined alloca
# define alloca __builtin_alloca
#endif
#elif defined _AIX
# define alloca __alloca
#elif defined _MSC_VER
# include <malloc.h>
# define alloca _alloca
#else
# ifndef HAVE_ALLOCA
# ifdef __cplusplus
extern "C"
# endif
void *alloca (size_t);
# endif
#endif
typedef struct SpiceChunk {
uint8_t *data;
uint32_t len;
} SpiceChunk;
enum {
SPICE_CHUNKS_FLAGS_UNSTABLE = (1<<0),
SPICE_CHUNKS_FLAGS_FREE = (1<<1)
};
typedef struct SpiceChunks {
uint32_t data_size;
uint32_t num_chunks;
uint32_t flags;
SpiceChunk chunk[0];
} SpiceChunks;
typedef struct SpiceBuffer
{
size_t capacity;
size_t offset;
uint8_t *buffer;
} SpiceBuffer;
char *spice_strdup(const char *str) SPICE_GNUC_MALLOC;
char *spice_strndup(const char *str, size_t n_bytes) SPICE_GNUC_MALLOC;
void *spice_memdup(const void *mem, size_t n_bytes) SPICE_GNUC_MALLOC;
void *spice_malloc(size_t n_bytes) SPICE_GNUC_MALLOC SPICE_GNUC_ALLOC_SIZE(1);
void *spice_malloc0(size_t n_bytes) SPICE_GNUC_MALLOC SPICE_GNUC_ALLOC_SIZE(1);
void *spice_realloc(void *mem, size_t n_bytes) SPICE_GNUC_WARN_UNUSED_RESULT;
void *spice_malloc_n(size_t n_blocks, size_t n_block_bytes) SPICE_GNUC_MALLOC SPICE_GNUC_ALLOC_SIZE2(1,2);
void *spice_malloc_n_m(size_t n_blocks, size_t n_block_bytes, size_t extra_size) SPICE_GNUC_MALLOC;
void *spice_malloc0_n(size_t n_blocks, size_t n_block_bytes) SPICE_GNUC_MALLOC SPICE_GNUC_ALLOC_SIZE2(1,2);
void *spice_realloc_n(void *mem, size_t n_blocks, size_t n_block_bytes) SPICE_GNUC_WARN_UNUSED_RESULT;
SpiceChunks *spice_chunks_new(uint32_t count) SPICE_GNUC_MALLOC;
SpiceChunks *spice_chunks_new_linear(uint8_t *data, uint32_t len) SPICE_GNUC_MALLOC;
void spice_chunks_destroy(SpiceChunks *chunks);
void spice_chunks_linearize(SpiceChunks *chunks);
size_t spice_strnlen(const char *str, size_t max_len);
/* Optimize: avoid the call to the (slower) _n function if we can
* determine at compile-time that no overflow happens.
*/
#if defined (__GNUC__) && (__GNUC__ >= 2) && defined (__OPTIMIZE__)
# define _SPICE_NEW(struct_type, n_structs, func) \
(struct_type *) (__extension__ ({ \
size_t __n = (size_t) (n_structs); \
size_t __s = sizeof (struct_type); \
void *__p; \
if (__s == 1) \
__p = spice_##func (__n); \
else if (__builtin_constant_p (__n) && \
__n <= SIZE_MAX / __s) \
__p = spice_##func (__n * __s); \
else \
__p = spice_##func##_n (__n, __s); \
__p; \
}))
# define _SPICE_RENEW(struct_type, mem, n_structs, func) \
(struct_type *) (__extension__ ({ \
size_t __n = (size_t) (n_structs); \
size_t __s = sizeof (struct_type); \
void *__p = (void *) (mem); \
if (__s == 1) \
__p = spice_##func (__p, __n); \
else if (__builtin_constant_p (__n) && \
__n <= SIZE_MAX / __s) \
__p = spice_##func (__p, __n * __s); \
else \
__p = spice_##func##_n (__p, __n, __s); \
__p; \
}))
#else
/* Unoptimized version: always call the _n() function. */
#define _SPICE_NEW(struct_type, n_structs, func) \
((struct_type *) spice_##func##_n ((n_structs), sizeof (struct_type)))
#define _SPICE_RENEW(struct_type, mem, n_structs, func) \
((struct_type *) spice_##func##_n (mem, (n_structs), sizeof (struct_type)))
#endif
/* Cast to a type with stricter alignment constraints (to build with clang) */
/* Misaligned cast to a type with stricter alignment */
#ifndef SPICE_DEBUG_ALIGNMENT
#define SPICE_UNALIGNED_CAST(type, value) ((type)(void *)(value))
#define SPICE_ALIGNED_CAST(type, value) ((type)(void *)(value))
#else // SPICE_DEBUG_ALIGNMENT
#define SPICE_ALIGNED_CAST(type, value) \
((type)spice_alignment_check(G_STRLOC, \
(void *)(value), \
__alignof(*((type)0))))
#define SPICE_UNALIGNED_CAST(type, value) \
((type)spice_alignment_weak_check(G_STRLOC, \
(void *)(value), \
__alignof(*((type)0))))
extern void spice_alignment_warning(const char *loc, void *p, unsigned sz);
extern void spice_alignment_debug(const char *loc, void *p, unsigned sz);
static inline void *spice_alignment_check(const char *loc,
void *ptr, unsigned sz)
{
if (G_UNLIKELY(((uintptr_t) ptr & (sz-1U)) != 0))
spice_alignment_warning(loc, ptr, sz);
return ptr;
}
static inline void *spice_alignment_weak_check(const char *loc,
void *ptr, unsigned sz)
{
if (G_UNLIKELY(((uintptr_t) ptr & (sz-1U)) != 0))
spice_alignment_debug(loc, ptr, sz);
return ptr;
}
#endif // SPICE_DEBUG_ALIGNMENT
#define spice_new(struct_type, n_structs) _SPICE_NEW(struct_type, n_structs, malloc)
#define spice_new0(struct_type, n_structs) _SPICE_NEW(struct_type, n_structs, malloc0)
#define spice_renew(struct_type, mem, n_structs) _SPICE_RENEW(struct_type, mem, n_structs, realloc)
/* Buffer management */
void spice_buffer_reserve(SpiceBuffer *buffer, size_t len);
int spice_buffer_empty(SpiceBuffer *buffer);
uint8_t *spice_buffer_end(SpiceBuffer *buffer);
void spice_buffer_reset(SpiceBuffer *buffer);
void spice_buffer_free(SpiceBuffer *buffer);
void spice_buffer_append(SpiceBuffer *buffer, const void *data, size_t len);
size_t spice_buffer_copy(SpiceBuffer *buffer, void *dest, size_t len);
size_t spice_buffer_remove(SpiceBuffer *buffer, size_t len);
SPICE_END_DECLS
#endif
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