gnu: re2c: Fix build on armhf-linux.

* gnu/packages/re2c.scm (re2c)[arguments]: When building for armhf-linux
add a phase to apply a patch.
* gnu/packages/patches/re2c-Use-maximum-alignment.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.

Change-Id: I9f056de47dc993b9ad779969f1eec71436c21160
Signed-off-by: Efraim Flashner <efraim@flashner.co.il>

2 files changed, 63 insertions, 1 deletions

diff --git a/gnu/packages/patches/re2c-Use-maximum-alignment.patch b/gnu/packages/patches/re2c-Use-maximum-alignment.patch
new file mode 100644
index 00000000000..6d5b95354fb
--- /dev/null
+++ b/gnu/packages/patches/re2c-Use-maximum-alignment.patch
@@ -0,0 +1,48 @@
+https://github.com/skvadrik/re2c/pull/555
+
+From 44125b74628d17f0a0a6cf9b51dd1f24169cd2d5 Mon Sep 17 00:00:00 2001
+From: Alexey Abramov <levenson@mmer.org>
+Date: Fri, 22 Aug 2025 08:10:08 +0200
+Subject: [PATCH] Use maximum alignment to ensure compatibility across all
+ architectures.
+
+---
+ src/util/allocator.h | 14 ++++++++++----
+ 1 file changed, 10 insertions(+), 4 deletions(-)
+
+diff --git a/src/util/allocator.h b/src/util/allocator.h
+index e6c85585b..56daf056f 100644
+--- a/src/util/allocator.h
++++ b/src/util/allocator.h
+@@ -3,6 +3,7 @@
+ 
+ #include <stdint.h>
+ #include <stdlib.h>
++#include <stddef.h>
+ #include <algorithm>
+ #include <vector>
+ 
+@@ -78,11 +79,16 @@ class slab_allocator_t {
+ };
+ 
+ // Use maximum alignment.
++// Use alignment based on pointer size: 32-bit platforms need stronger alignment
++// for 64-bit types (double, long long), while 64-bit platforms are already
++// sufficiently aligned with pointer-sized alignment.
++constexpr size_t ALLOCATOR_ALIGNMENT = (sizeof(void*) == 4) ? alignof(max_align_t) : sizeof(void*);
++
+ // Use different types to prevent accidentally mixing allocators for data with different life spans.
+-using AstAllocator = slab_allocator_t<AllocatorKind::AST, 16 * 4096, sizeof(void*)>;
+-using IrAllocator = slab_allocator_t<AllocatorKind::IR, 16 * 4096, sizeof(void*)>;
+-using DfaAllocator = slab_allocator_t<AllocatorKind::DFA, 16 * 4096, sizeof(void*)>;
+-using OutAllocator = slab_allocator_t<AllocatorKind::OUT, 16 * 4096, sizeof(void*)>;
++using AstAllocator = slab_allocator_t<AllocatorKind::AST, 16 * 4096, ALLOCATOR_ALIGNMENT>;
++using IrAllocator = slab_allocator_t<AllocatorKind::IR, 16 * 4096, ALLOCATOR_ALIGNMENT>;
++using DfaAllocator = slab_allocator_t<AllocatorKind::DFA, 16 * 4096, ALLOCATOR_ALIGNMENT>;
++using OutAllocator = slab_allocator_t<AllocatorKind::OUT, 16 * 4096, ALLOCATOR_ALIGNMENT>;
+ 
+ } // namespace re2c
+ 
+-- 
+2.50.1
+
diff --git a/gnu/packages/re2c.scm b/gnu/packages/re2c.scm
index 7ff0dd9e4b9..3eb898dd4c9 100644
--- a/gnu/packages/re2c.scm
+++ b/gnu/packages/re2c.scm
@@ -2,6 +2,7 @@
 ;;; Copyright © 2017, 2020 Sergei Trofimovich <slyfox@inbox.ru>
 ;;; Copyright © 2021 Sergei Trofimovich <slyich@gmail.com>
 ;;; Copyright © 2018 Tobias Geerinckx-Rice <me@tobias.gr>
+;;; Copyright © 2025 Alexey Abramov <levenson@mmer.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -20,7 +21,10 @@
 
 (define-module (gnu packages re2c)
   #:use-module (guix licenses)
+  #:use-module (guix gexp)
+  #:use-module (guix utils)
   #:use-module (guix packages)
+  #:use-module (gnu packages)
   #:use-module (gnu packages python)
   #:use-module (guix download)
   #:use-module (guix build-system gnu))
@@ -38,9 +42,19 @@
               (base32
                 "07ysqgdm0h566a8lwnpdgycp93vz7zskzihsgah3bla0ycj2pp69"))))
     (build-system gnu-build-system)
-    (home-page "https://re2c.org/")
+    (arguments
+     (if (target-arm32?)
+         (list #:phases
+               #~(modify-phases %standard-phases
+                   (add-after 'unpack 'patch-sources
+                     (lambda _
+                       (invoke "patch" "-p1" "--force" "--input"
+                               #$(local-file (search-patch
+                                               "re2c-Use-maximum-alignment.patch")))))))
+         '()))
     (native-inputs
      (list python))             ; for the test driver
+    (home-page "https://re2c.org/")
     (synopsis "Lexer generator for C/C++")
     (description
      "@code{re2c} generates minimalistic hard-coded state machine (as opposed