Apple: MaterialX on Metal#2324
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Filed as internal issue #USD-8085 |
pixar-oss
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This version update allows for MaterialX support on Metal. Fixes #2324 (Internal change: 2275891)
musicinmybrain
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…expansion (PixarAnimationStudios#2324) * Fix misaligned memory access in `LossyDctDecoder_execute` HALF→FLOAT expansion After DCT decoding, `LossyDctDecoder_execute()` expands FLOAT-type channels from their intermediate HALF (16-bit) XDR representation back to FLOAT (32-bit) XDR in place. The expansion was done by casting `_rows[y]` (a `uint8_t *`) directly to `float *` and `uint16_t *`, then reading and writing through those typed pointers. Because row buffers are assigned by advancing a byte pointer with no alignment padding (`outBufferEnd += chan->width * chan->bytes_per_element` in `internal_dwa_compressor.h`), a FLOAT channel that follows a HALF channel of odd width receives a `_rows[y]` pointer that is 2-byte aligned but not 4-byte aligned. Dereferencing a `float *` cast from such a pointer is undefined behavior under the C standard: - On ARM, RISC-V, and MIPS (strict alignment) this crashes immediately. - On x86 it is silently tolerated at the hardware level but remains UB: auto-vectorizing compilers (SSE/AVX) may assume aligned access and generate incorrect code. - UBSan reports: `store to misaligned address ... for type 'float', which requires 4 byte alignment` at `internal_dwa_decoder.h:749`. Fix: replace the cast-and-dereference pattern with the `unaligned_load16` / `memcpy` / `unaligned_store32` helpers already used throughout the rest of OpenEXRCore (`internal_xdr.h`, `unpack.c`, `pack.c`, `internal_pxr24.c`). These helpers use `memcpy` internally, which the C standard guarantees is safe for unaligned addresses and which compilers compile to a single load/store instruction on architectures that support it. The byte-order handling is preserved correctly: - `unaligned_load16` reads 2 bytes via `memcpy` and applies `one_to_native16` (XDR → native), returning a native-endian HALF value. - `half_to_float` converts native HALF → native float. - `memcpy(&bits, &f, 4)` reinterprets the float's bit pattern as `uint32_t` without numeric conversion (the correct type-pun idiom in C). - `unaligned_store32` applies `one_from_native32` (native → XDR) and writes 4 bytes via `memcpy`, storing the result in XDR float format. Made-with: Cursor Signed-off-by: Cary Phillips <cary@ilm.com> * add TODO comment Signed-off-by: Cary Phillips <cary@ilm.com> --------- Signed-off-by: Cary Phillips <cary@ilm.com>
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Description of Change(s)
Co-authored by:
Morteza Mostajabodaveh
Jon Creighton