diff options
| -rw-r--r-- | src/H5Tconv.c | 24 |
1 files changed, 22 insertions, 2 deletions
diff --git a/src/H5Tconv.c b/src/H5Tconv.c index 93ca59f..8118eb0 100644 --- a/src/H5Tconv.c +++ b/src/H5Tconv.c @@ -887,7 +887,17 @@ done: /* Macro defining action on source data which needs to be aligned (before main action) */ #define H5T_CONV_LOOP_PRE_SALIGN(ST) \ { \ - H5MM_memcpy(&src_aligned, src, sizeof(ST)); \ + /* The uint8_t * cast is required to avoid tripping over undefined behavior. \ + * \ + * The typed pointer arrives via a void pointer, which may have any alignment. \ + * We then cast it to a pointer to a type that is assumed to be aligned, which \ + * is undefined behavior (section 6.3.2.3 paragraph 7 of the C99 standard). \ + * In the past this hasn't caused many problems, but in some cases (e.g. \ + * converting long doubles on macOS), an optimizing compiler might do the \ + * wrong thing (in the macOS case, the conversion uses SSE, which has stricter \ + * requirements about alignment). \ + */ \ + H5MM_memcpy(&src_aligned, (const uint8_t *)src, sizeof(ST)); \ } /* Macro defining action on source data which doesn't need to be aligned (before main action) */ @@ -919,7 +929,17 @@ done: /* Macro defining action on destination data which needs to be aligned (after main action) */ #define H5T_CONV_LOOP_POST_DALIGN(DT) \ { \ - H5MM_memcpy(dst, &dst_aligned, sizeof(DT)); \ + /* The uint8_t * cast is required to avoid tripping over undefined behavior. \ + * \ + * The typed pointer arrives via a void pointer, which may have any alignment. \ + * We then cast it to a pointer to a type that is assumed to be aligned, which \ + * is undefined behavior (section 6.3.2.3 paragraph 7 of the C99 standard). \ + * In the past this hasn't caused many problems, but in some cases (e.g. \ + * converting long doubles on macOS), an optimizing compiler might do the \ + * wrong thing (in the macOS case, the conversion uses SSE, which has stricter \ + * requirements about alignment). \ + */ \ + H5MM_memcpy((uint8_t *)dst, &dst_aligned, sizeof(DT)); \ } /* Macro defining action on destination data which doesn't need to be aligned (after main action) */ |