Commit efb1ccad authored by Matt Turner's avatar Matt Turner

util/ralloc: Make sizeof(linear_header) a multiple of 8

Prior to this patch sizeof(linear_header) was 20 bytes in a
non-debug build on 32-bit platforms. We do some pointer arithmetic to
calculate the next available location with

   ptr = (linear_size_chunk *)((char *)&latest[1] + latest->offset);

in linear_alloc_child(). The &latest[1] adds 20 bytes, so an allocation
would only be 4-byte aligned.

On 32-bit SPARC a 'sttw' instruction (which stores a consecutive pair of
4-byte registers to memory) requires an 8-byte aligned address. Such an
instruction is used to store to an 8-byte integer type, like intmax_t
which is used in glcpp's expression_value_t struct.

As a result of the 4-byte alignment returned by linear_alloc_child() we
would generate a SIGBUS (unaligned exception) on SPARC.

According to the GNU libc manual malloc() always returns memory that has
at least an alignment of 8-bytes [1]. I think our allocator should do
the same.

So, simple fix with two parts:

   (1) Increase SUBALLOC_ALIGNMENT to 8 unconditionally.
   (2) Mark linear_header with an aligned attribute, which will cause
       its sizeof to be rounded up to that alignment. (We already do
       this for ralloc_header)

With this done, all Mesa's unit tests now pass on SPARC.

[1] https://www.gnu.org/software/libc/manual/html_node/Aligned-Memory-Blocks.html

Fixes: 47e17586 ("glcpp: use the linear allocator for most objects")
Bug: https://bugs.gentoo.org/636326Reviewed-by: Eric Anholt's avatarEric Anholt <eric@anholt.net>
parent 7e3748c2
......@@ -552,10 +552,18 @@ ralloc_vasprintf_rewrite_tail(char **str, size_t *start, const char *fmt,
*/
#define MIN_LINEAR_BUFSIZE 2048
#define SUBALLOC_ALIGNMENT sizeof(uintptr_t)
#define SUBALLOC_ALIGNMENT 8
#define LMAGIC 0x87b9c7d3
struct linear_header {
struct
#ifdef _MSC_VER
__declspec(align(8))
#elif defined(__LP64__)
__attribute__((aligned(16)))
#else
__attribute__((aligned(8)))
#endif
linear_header {
#ifndef NDEBUG
unsigned magic; /* for debugging */
#endif
......@@ -647,6 +655,8 @@ linear_alloc_child(void *parent, unsigned size)
ptr = (linear_size_chunk *)((char*)&latest[1] + latest->offset);
ptr->size = size;
latest->offset += full_size;
assert((uintptr_t)&ptr[1] % SUBALLOC_ALIGNMENT == 0);
return &ptr[1];
}
......
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