From abecb5bb408f253cd24345ba94940ea0f7b59f4f Mon Sep 17 00:00:00 2001
From: Ondrej Zajicek <santiago@crfreenet.org>
Date: Thu, 9 Jan 2025 16:44:51 +0100
Subject: [PATCH] lib: Unify alignment of allocators

Different internal allocators (memory blocks, linpools, and slabs) used
different way to compute alignment. Unify it to use alignment based on
standard max_align_t type.

On x86_64, this does not change alignment of memory blocks and linpools
(both old and new is 16), but it increases alignment of slabs from 8 to
16.

Minor changes by commiter.
---
 lib/birdlib.h  |  5 ++---
 lib/mempool.c  |  2 +-
 lib/resource.c |  2 +-
 lib/slab.c     | 11 ++---------
 4 files changed, 6 insertions(+), 14 deletions(-)

diff --git a/lib/birdlib.h b/lib/birdlib.h
index da8985c7..8209a108 100644
--- a/lib/birdlib.h
+++ b/lib/birdlib.h
@@ -10,17 +10,16 @@
 #define _BIRD_BIRDLIB_H_
 
 #include "lib/alloca.h"
+#include <stddef.h>
 #include <stdarg.h>
 #include <stdalign.h>
 
 /* Ugly structure offset handling macros */
 
-struct align_probe { char x; long int y; };
-
 #define OFFSETOF(s, i) ((size_t) &((s *)0)->i)
 #define SKIP_BACK(s, i, p) ((s *)((char *)p - OFFSETOF(s, i)))
 #define BIRD_ALIGN(s, a) (((s)+a-1)&~(a-1))
-#define CPU_STRUCT_ALIGN (sizeof(struct align_probe))
+#define CPU_STRUCT_ALIGN (alignof(max_align_t))
 
 /* Utility macros */
 
diff --git a/lib/mempool.c b/lib/mempool.c
index 1c02d64a..525eee8f 100644
--- a/lib/mempool.c
+++ b/lib/mempool.c
@@ -27,7 +27,7 @@
 
 struct lp_chunk {
   struct lp_chunk *next;
-  uintptr_t data_align[0];
+  max_align_t data_align[0];
   byte data[0];
 };
 
diff --git a/lib/resource.c b/lib/resource.c
index b1a3df10..7d1b6df4 100644
--- a/lib/resource.c
+++ b/lib/resource.c
@@ -316,7 +316,7 @@ resource_init(void)
 struct mblock {
   resource r;
   unsigned size;
-  uintptr_t data_align[0];
+  max_align_t data_align[0];
   byte data[0];
 };
 
diff --git a/lib/slab.c b/lib/slab.c
index 6a4573a3..68b6c485 100644
--- a/lib/slab.c
+++ b/lib/slab.c
@@ -68,7 +68,7 @@ static struct resclass sl_class = {
 
 struct sl_obj {
   node n;
-  uintptr_t data_align[0];
+  max_align_t data_align[0];
   byte data[0];
 };
 
@@ -168,11 +168,6 @@ struct sl_head {
   u32 used_bits[0];
 };
 
-struct sl_alignment {			/* Magic structure for testing of alignment */
-  byte data;
-  int x[0];
-};
-
 #define TLIST_PREFIX sl_head
 #define TLIST_TYPE   struct sl_head
 #define TLIST_ITEM   n
@@ -219,9 +214,7 @@ slab *
 sl_new(pool *p, uint size)
 {
   slab *s = ralloc(p, &sl_class);
-  uint align = sizeof(struct sl_alignment);
-  if (align < sizeof(void *))
-    align = sizeof(void *);
+  uint align = CPU_STRUCT_ALIGN;
   s->data_size = size;
   size = (size + align - 1) / align * align;
   s->obj_size = size;