sys-devel/flex: fix crash on Apple M1 due to undefined behavior.

Currently, when the NULL-terminated variadic function
filter_create_ext() is invoked, the value "0" is passed as
the last argument to act as a terminator. However, this is
an integer value, which is incompatible with the pointer
data type expected by filter_create_ext().

This is undefined behavior in C, correct operation is not
guaranteed. In fact, it causes flex to crash on Apple M1
when GCC is used - the loop is not terminated when it should,
instead, it keeps running, corrupting the argument list for
invoking m4. As a result, it creates the following error:

> flex: fatal internal error, exec of gm4 failed

This commit fixes the problem by explicitly casting the value
0 to the correct pointer type (char *).

Since the existence of the bug doesn't always prevent a Gentoo
Prefix bootstrapping, it can lurk inside the system and remain
undetected, furthermore, it's technically a C programming bug,
other platforms could've been affected as well in theory. Thus,
we also bump the package version.

Closes: https://bugs.gentoo.org/871324
Signed-off-by: Yifeng Li <tomli@tomli.me>
Signed-off-by: Sam James <sam@gentoo.org>

2 files changed, 149 insertions, 0 deletions

diff --git a/sys-devel/flex/files/flex-2.6.4-fix-apple-m1-crash-by-explicit-pointer-cast.patch b/sys-devel/flex/files/flex-2.6.4-fix-apple-m1-crash-by-explicit-pointer-cast.patch
new file mode 100644
index 000000000000..c594262d2cb0
--- /dev/null
+++ b/sys-devel/flex/files/flex-2.6.4-fix-apple-m1-crash-by-explicit-pointer-cast.patch
@@ -0,0 +1,48 @@
+https://github.com/westes/flex/issues/539
+https://github.com/westes/flex/pull/554
+https://bugs.gentoo.org/871324
+
+This is a backported version for applying to v2.6.4
+instead of git.
+
+From cce2df853386d5b5b60445b1204dcca08e9f259e Mon Sep 17 00:00:00 2001
+From: Yifeng Li <tomli@tomli.me>
+Date: Mon, 20 Feb 2023 11:23:52 +0000
+Subject: [PATCH] Fix #539 crash on Apple M1 by casting 0 to (char *)
+ explicitly
+
+Currently, when the NULL-terminated variadic function
+filter_create_ext() is invoked, the value "0" is passed as
+the last argument to act as a terminator. However, this is
+an integer value, which is incompatible with the pointer
+data type expected by filter_create_ext().
+
+This is undefined behavior in C, correct operation is not
+guaranteed. In fact, it causes flex to crash on Apple M1
+when GCC is used - the loop is not terminated when it should,
+instead, it keeps running, corrupting the argument list for
+invoking m4. As a result, it creates the following error:
+
+> flex: fatal internal error, exec of gm4 failed
+
+This commit fixes the problem by explicitly casting the value 0 to
+the correct pointer type (char *).
+
+Signed-off-by: Yifeng Li <tomli@tomli.me>
+---
+ src/main.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/src/main.c b/src/main.c
+index e5eac44fe..5c9086183 100644
+--- a/src/main.c
++++ b/src/main.c
+@@ -380,7 +380,7 @@ void check_options (void)
+ 			}
+ 		}
+ 	}
+-    filter_create_ext(output_chain, m4, "-P", 0);
++    filter_create_ext(output_chain, m4, "-P", (char *) 0);
+     filter_create_int(output_chain, filter_fix_linedirs, NULL);
+ 
+     /* For debugging, only run the requested number of filters. */
diff --git a/sys-devel/flex/flex-2.6.4-r6.ebuild b/sys-devel/flex/flex-2.6.4-r6.ebuild
new file mode 100644
index 000000000000..6da72c3dfe33
--- /dev/null
+++ b/sys-devel/flex/flex-2.6.4-r6.ebuild
@@ -0,0 +1,101 @@
+# Copyright 1999-2022 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=8
+
+inherit flag-o-matic libtool multilib-minimal toolchain-funcs
+
+DESCRIPTION="The Fast Lexical Analyzer"
+HOMEPAGE="https://github.com/westes/flex"
+SRC_URI="https://github.com/westes/${PN}/releases/download/v${PV}/${P}.tar.gz"
+SRC_URI+=" https://dev.gentoo.org/~sam/distfiles/${CATEGORY}/${PN}/${P}-autotools-regenerate.patch.xz"
+
+LICENSE="FLEX"
+SLOT="0"
+KEYWORDS="~alpha amd64 arm arm64 hppa ~ia64 ~loong ~m68k ~mips ppc ppc64 ~riscv ~s390 sparc x86 ~x64-cygwin ~amd64-linux ~x86-linux ~ppc-macos ~x64-macos ~sparc-solaris ~sparc64-solaris ~x64-solaris ~x86-solaris"
+IUSE="nls static test"
+RESTRICT="!test? ( test )"
+
+RDEPEND="sys-devel/m4"
+# We want bison explicitly and not yacc in general, bug #381273
+BDEPEND="
+	${RDEPEND}
+	nls? ( sys-devel/gettext )
+	test? ( sys-devel/bison )
+"
+PDEPEND="app-alternatives/lex"
+
+PATCHES=(
+	"${FILESDIR}"/${P}-libobjdir.patch
+	"${FILESDIR}"/${P}-fix-build-with-glibc2.26.patch
+	"${FILESDIR}"/${P}-fix-apple-m1-crash-by-explicit-pointer-cast.patch
+
+	"${WORKDIR}"/${P}-autotools-regenerate.patch
+)
+
+src_prepare() {
+	default
+
+	# Drop on next release when we can remove ${P}-autotools-regenerate.patch
+	touch configure.ac aclocal.m4 Makefile.in configure src/config.h.in || die
+
+	# Disable running in the tests/ subdir as it has a bunch of built sources
+	# that cannot be made conditional (automake limitation). bug #568842
+	if ! use test ; then
+		sed -i \
+			-e '/^SUBDIRS =/,/^$/{/tests/d}' \
+			Makefile.in || die
+	fi
+
+	# Prefix always needs this
+	elibtoolize
+}
+
+src_configure() {
+	use static && append-ldflags -static
+
+	multilib-minimal_src_configure
+}
+
+multilib_src_configure() {
+	# Do not install shared libs, #503522
+	ECONF_SOURCE="${S}" econf \
+		CC_FOR_BUILD="$(tc-getBUILD_CC)" \
+		--disable-shared \
+		$(use_enable nls)
+}
+
+multilib_src_compile() {
+	if multilib_is_native_abi; then
+		default
+	else
+		emake -C src -f Makefile -f - lib <<< 'lib: $(lib_LTLIBRARIES)'
+	fi
+}
+
+multilib_src_test() {
+	multilib_is_native_abi && emake check
+}
+
+multilib_src_install() {
+	if multilib_is_native_abi; then
+		default
+	else
+		emake -C src DESTDIR="${D}" install-libLTLIBRARIES install-includeHEADERS
+	fi
+}
+
+multilib_src_install_all() {
+	einstalldocs
+	dodoc ONEWS
+	find "${ED}" -name '*.la' -type f -delete || die
+	rm "${ED}"/usr/share/doc/${PF}/COPYING || die
+}
+
+pkg_postinst() {
+	# ensure to preserve the symlink before app-alternatives/lex
+	# is installed
+	if [[ ! -h ${EROOT}/usr/bin/lex ]]; then
+		ln -s flex "${EROOT}/usr/bin/lex" || die
+	fi
+}