https://bugs.gentoo.org/820071
https://git.kernel.org/pub/scm/libs/libcap/libcap.git/patch/?id=c234bf90839f19e0332b586335411cb626a25a18
https://git.kernel.org/pub/scm/libs/libcap/libcap.git/patch/?id=e9414f540a82b5348a12cfaddff229241564e1f3

From: "Andrew G. Morgan" <morgan@kernel.org>
Date: Sat, 13 Nov 2021 20:38:18 -0800
Subject: Work around a __i386__ compilation issue for runnable .so files.

This was reported by Sam James and debugged with respect to:

  https://bugs.gentoo.org/show_bug.cgi?id=820071

Modern versions of glibc employ SSE instructions that require the
stack to be aligned to 16 bytes in order to execute movaps and
friends to stack stored memory. The ABI for x86_64 requires this
alignment so we'd not seen this issue before being cc:d into the
bug.

Signed-off-by: Andrew G. Morgan <morgan@kernel.org>
--- a/libcap/execable.h
+++ b/libcap/execable.h
@@ -74,20 +74,26 @@ static void __execable_parse_args(int *argc_p, char ***argv_p)
  * Note, to avoid any runtime confusion, SO_MAIN is a void static
  * function.
  */
+#if defined(__i386__)
+#define __SO_FORCE_ARG_ALIGNMENT  __attribute__((force_align_arg_pointer))
+#else
+#define __SO_FORCE_ARG_ALIGNMENT
+#endif /* def __i386 */
 
-#define SO_MAIN						        \
-static void __execable_main(int, char**);                       \
-extern void __so_start(void);		                	\
-void __so_start(void)                                           \
-{                                                               \
-    int argc;                                                   \
-    char **argv;                                                \
-    __execable_parse_args(&argc, &argv);                        \
+#define SO_MAIN							\
+static void __execable_main(int, char**);			\
+extern void __so_start(void);					\
+__SO_FORCE_ARG_ALIGNMENT					\
+void __so_start(void)						\
+{								\
+    int argc;							\
+    char **argv;						\
+    __execable_parse_args(&argc, &argv);			\
     __execable_main(argc, argv);				\
-    if (argc != 0) {                                            \
-	free(argv[0]);                                          \
-	free(argv);                                             \
-    }                                                           \
-    exit(0);                                                    \
-}                                                               \
+    if (argc != 0) {						\
+	free(argv[0]);						\
+	free(argv);						\
+    }								\
+    exit(0);							\
+}								\
 static void __execable_main

From: "Andrew G. Morgan" <morgan@kernel.org>
Date: Sun, 14 Nov 2021 20:38:30 -0800
Subject: Work around musl not hard-coding the ABI for Linux x86_64.

There seems to be a subtle difference between glibc and musl over
whether or not a runnable *.so needs to start out with its stack
aligned to 16 bytes or not. Since Linux ABIs for x86 (both 32 and
64 bit varieties) require 16 byte alignment, just force it on both
these architectures.

This addresses:

  https://bugzilla.kernel.org/show_bug.cgi?id=215009

Signed-off-by: Andrew G. Morgan <morgan@kernel.org>
--- a/libcap/execable.h
+++ b/libcap/execable.h
@@ -71,15 +71,19 @@ static void __execable_parse_args(int *argc_p, char ***argv_p)
 }
 
 /*
- * Note, to avoid any runtime confusion, SO_MAIN is a void static
- * function.
+ * Linux x86 ABI requires the stack be 16 byte aligned. Keep things
+ * simple and just force it.
  */
-#if defined(__i386__)
+#if defined(__i386__) || defined(__x86_64__)
 #define __SO_FORCE_ARG_ALIGNMENT  __attribute__((force_align_arg_pointer))
 #else
 #define __SO_FORCE_ARG_ALIGNMENT
-#endif /* def __i386 */
+#endif /* def some x86 */
 
+/*
+ * Note, to avoid any runtime confusion, SO_MAIN is a void static
+ * function.
+ */
 #define SO_MAIN							\
 static void __execable_main(int, char**);			\
 extern void __so_start(void);					\
cgit 1.2.3-1.el7