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scratch_buffer: use union for internal buffer

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Problem reported by Florian Weimer [1] and solution suggested by
Andreas Schwab [2].  It also set the same buffer size independent
of architecture max_align_t size.

Checked on x86_64-linux-gnu and i686-linux-gnu.

	* lib/malloc/scratch_buffer.h (struct scratch_buffer):
	Use an union instead of a max_align_t array for __space,
	so that __space is the same size on all platforms.
	* malloc/scratch_buffer_grow_preserve.c
	(__libc_scratch_buffer_grow_preserve): Likewise.

[1] https://sourceware.org/ml/libc-alpha/2017-09/msg00693.html
[2] https://sourceware.org/ml/libc-alpha/2017-09/msg00695.html
This commit is contained in:
Adhemerval Zanella 2017-09-18 09:26:00 -03:00
parent ccf970c7a7
commit 5f9f31ad12
4 changed files with 12 additions and 6 deletions
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6
ChangeLog
View File

@ -1,5 +1,11 @@
2017-09-25 Adhemerval Zanella <adhemerval.zanella@linaro.org>
* lib/malloc/scratch_buffer.h (struct scratch_buffer):
Use an union instead of a max_align_t array for __space,
so that __space is the same size on all platforms.
* malloc/scratch_buffer_grow_preserve.c
(__libc_scratch_buffer_grow_preserve): Likewise.
[BZ #22183]
* include/gnu-versions.h (_GNU_GLOB_INTERFACE_VERSION): Increase
version to 2.

6
include/scratch_buffer.h
View File

@ -66,7 +66,7 @@
struct scratch_buffer {
void *data; /* Pointer to the beginning of the scratch area. */
size_t length; /* Allocated space at the data pointer, in bytes. */
max_align_t __space[(1023 + sizeof (max_align_t)) / sizeof (max_align_t)];
union { max_align_t __align; char __c[1024]; } __space;
};
/* Initializes *BUFFER so that BUFFER->data points to BUFFER->__space
@ -74,7 +74,7 @@ struct scratch_buffer {
static inline void
scratch_buffer_init (struct scratch_buffer *buffer)
{
buffer->data = buffer->__space;
buffer->data = buffer->__space.__c;
buffer->length = sizeof (buffer->__space);
}
@ -82,7 +82,7 @@ scratch_buffer_init (struct scratch_buffer *buffer)
static inline void
scratch_buffer_free (struct scratch_buffer *buffer)
{
if (buffer->data != buffer->__space)
if (buffer->data != buffer->__space.__c)
free (buffer->data);
}

4
malloc/scratch_buffer_grow_preserve.c
View File

@ -30,14 +30,14 @@ __libc_scratch_buffer_grow_preserve (struct scratch_buffer *buffer)
size_t new_length = 2 * buffer->length;
void *new_ptr;
if (buffer->data == buffer->__space)
if (buffer->data == buffer->__space.__c)
{
/* Move buffer to the heap. No overflow is possible because
buffer->length describes a small buffer on the stack. */
new_ptr = malloc (new_length);
if (new_ptr == NULL)
return false;
memcpy (new_ptr, buffer->__space, buffer->length);
memcpy (new_ptr, buffer->__space.__c, buffer->length);
}
else
{

2
malloc/tst-scratch_buffer.c
View File

@ -59,7 +59,7 @@ array_size_must_fail (size_t a, size_t b)
pass, a, b);
return false;
}
if (buf.data != buf.__space)
if (buf.data != buf.__space.__c)
{
printf ("scratch_buffer_set_array_size did not free: %d %zu %zu\n",
pass, a, b);