compiler: Support long UTF-8 encoded atoms #8913
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CT Test Results 5 files 538 suites 1h 46m 46s ⏱️ Results for commit 04b168d. ♻️ This comment has been updated with latest results. To speed up review, make sure that you have read Contributing to Erlang/OTP and that all checks pass. See the TESTING and DEVELOPMENT HowTo guides for details about how to run test locally. Artifacts// Erlang/OTP Github Action Bot |
Support for atoms containing any Unicode code point was added
in Erlang/OTP 20 (PR-1078).
After that change, an atom can contain up to 255 Unicode code
points. However, atoms used in Erlang source code is still limited to
255 bytes because the atom table in the BEAM file only has a byte for
holding the length in bytes of the atom text. For instance, the `🟦`
character has a four-byte encoding (`<<240,159,159,166>>`), meaning
that Erlang source code containing a literal atom consisting of 64 or
more such characters cannot be compiled.
This commit changes the atom table in BEAM files to use a variable
length encoding for the length of each atom. For atoms up to 15 bytes,
the length is encoded in one byte. The header for the atom table is
also changed to indicate that new encoding of lengths are used.
Attempting to load a BEAM file compiled with Erlang/OTP 28 in
Erlang/OTP 27 or earlier will result in the following error message:
1> l(t).
=ERROR REPORT==== 8-Oct-2024::08:49:01.750424 ===
beam/beam_load.c(150): Error loading module t:
corrupt atom table
{error,badfile}
`beam_lib` is updated to handle the new format. External tools that
use `beam_lib:chunks(Beam, [atoms])` to read the atom table will
continue to work. External tools that do their own parsing of the atom
table will need to be updated.
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jhogberg
approved these changes
Oct 8, 2024
This was referenced Oct 13, 2024
bettio
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Oct 13, 2024
CI: build-and-test: disable OTP master A recent change made impossible to use beam files compiled with OTP master, so let's disable it. See also #1321 and erlang/otp#8913 These changes are made under both the "Apache 2.0" and the "GNU Lesser General Public License 2.1 or later" license terms (dual license). SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
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Support for atoms containing any Unicode code point was added in Erlang/OTP 20 (#1078).
After that change, an atom can contain up to 255 Unicode code points. However, atoms used in Erlang source code is still limited to 255 bytes because the atom table in the BEAM file only has a byte for holding the length in bytes of the atom text. For instance, the
🟦character has a four-byte encoding (<<240,159,159,166>>), meaning that Erlang source code containing a literal atom consisting of 64 or more such characters cannot be compiled.This pull request changes the atom table in BEAM files to use
two bytesa variable length encoding for the length of each atom. For atoms up to 15 bytes, the length is encoded in one byte. The header for the atom table is also changed to indicate thattwo-byte lengththe new encodiging of lengths are used. Attempting to load a BEAM file compiled with Erlang/OTP 28 in Erlang/OTP 27 or earlier will result in the following error message:beam_libis updated to handle the new format. External tools that usebeam_lib:chunks(Beam, [atoms])to read the atom table will continue to work. External tools that do their own parsing of the atom table will need to be updated.