Matt Turner <matts...@gmail.com> writes: > 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: 47e17586924f ("glcpp: use the linear allocator for most objects") > Bug: https://bugs.gentoo.org/636326 > --- > src/util/ralloc.c | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/src/util/ralloc.c b/src/util/ralloc.c > index 745b4cf1226..fc35661996d 100644 > --- a/src/util/ralloc.c > +++ b/src/util/ralloc.c > @@ -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]; > }
These patches are: Reviewed-by: Eric Anholt <e...@anholt.net> However, shouldn't we also bump SUBALLOC_ALIGNMENT to 16 on LP64, too, if that's what glibc is doing for malloc?
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