[tfenne]

char is signed on x86-64 and Apple arm64 but unsigned on Linux aarch64, and TileDB keeps signed values in chars. The array schema stores each compression level as a char, so on Linux aarch64 zlib's default level of −1 reads back as 255 and GZIP compression fails with Z_STREAM_ERROR, as in tiledb_array_write_dense_1. TILEDB_EMPTY_CHAR (CHAR_MAX), which marks missing char values on disk, is 255 there and 127 everywhere else, so missing values written on x86-64 or macOS read back on aarch64 as 127, and missing values written on aarch64 read back elsewhere as −1. This builds TileDB with -fsigned-char and adds it to the link interface of tiledb_static and tiledb_shared, so that code linking them, such as GenomicsDB, agrees on TILEDB_EMPTY_CHAR too, and adds a test that it is 127. CI has no aarch64 runner, so I checked it in an AlmaLinux 8 container on aarch64 with GCC 15 and clang 21, which need #12 to build: every test and example passes with this change, and tiledb_array_write_dense_1 fails without it.

@nalinigans, one thing needs your view: arrays already written on Linux aarch64 mark missing chars with 255, which after this change reads as −1 rather than as missing. If there are aarch64 users with existing workspaces, it would need at least a note in the release.

[tfenne]

Closing in favour of #14, which redefines TILEDB_EMPTY_CHAR as 0x7F as you suggested, rather than changing char's signedness. The compression-level fix this also carried is in #13.