main/libucontext: fix build with -Os on x86

See:

* https://github.com/kaniini/libucontext/issues/52#issuecomment-1936736286
* https://github.com/kaniini/libucontext/pull/60

main/libucontext/0001-common-trampoline-Ensure-omission-of-frame-pointer.patch

@@ -0,0 +1,47 @@
+From 13437174df7cd45873cf2d1d9c4c4277e2db8a5a Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?S=C3=B6ren=20Tempel?= <soeren+git@soeren-tempel.net>
+Date: Sat, 10 Feb 2024 00:13:28 +0100
+Subject: [PATCH] common-trampoline: Ensure omission of frame-pointer
+
+Some architecture-specific implementations of the FETCH_LINKPTR
+(e.g. the one for x86) attempt to find the linkptr relative to the
+stack pointer. Therefore, they make assumption about the value of
+the SP at the point where the FETCH_LINKPTR code is executed. This
+means that we don't want the C compiler to mess with our SP.
+
+For this purpose, local variables in this function are currently
+declared using the register storage specifier. Additionally, we
+need to make sure that a frame pointer is /always/ omitted for
+this function. On x86 Alpine, the frame pointer is presently not
+omitted with GCC 13 when using -Os, therefore the tests segfault
+with -Os on Alpine presently.
+
+Fixes #52
+---
+ arch/common/common-trampoline.c | 12 ++++++++++++
+ 1 file changed, 12 insertions(+)
+
+diff --git a/arch/common/common-trampoline.c b/arch/common/common-trampoline.c
+index 5b52327..41f994b 100644
+--- a/arch/common/common-trampoline.c
++++ b/arch/common/common-trampoline.c
+@@ -14,7 +14,19 @@
+ #include <stdlib.h>
+ #include <stdio.h>
+ 
++/* We need to make sure that the C compiler doesn't push any
++ * additional data to the stack frame. Otherwise, assumptions
++ * made by the architecture-specific implementation of the
++ * FETCH_LINKPTR() macro about the location of the linkptr,
++ * relative to the stack pointer, will not hold.
++ *
++ * Hence, we compile this function with -fomit-frame-pointer
++ * and use the register storage-class specifier for all local
++ * vars. Note that the latter is just a "suggestion" (see C99).
++ */
++
+ __attribute__ ((visibility ("hidden")))
++__attribute__ ((optimize ("omit-frame-pointer")))
+ void
+ libucontext_trampoline(void)
+ {

main/libucontext/APKBUILD

@@ -1,14 +1,15 @@
 # Maintainer: Ariadne Conill <ariadne@dereferenced.org>
 pkgname=libucontext
 pkgver=1.2
-pkgrel=2
+pkgrel=3
 pkgdesc="ucontext function implementations"
 url="https://github.com/kaniini/libucontext"
 arch="all"
 license="ISC"
 subpackages="$pkgname-dev $pkgname-doc"
 makedepends="scdoc"
-source="https://distfiles.ariadne.space/libucontext/libucontext-$pkgver.tar.xz"
+source="https://distfiles.ariadne.space/libucontext/libucontext-$pkgver.tar.xz
+	0001-common-trampoline-Ensure-omission-of-frame-pointer.patch"
 
 case "$CTARGET_ARCH" in
 	arm*)		LIBUCONTEXT_ARCH="arm" ;;
@@ -17,10 +18,6 @@ case "$CTARGET_ARCH" in
 esac
 
 build() {
-	# workaround segfault on x86 with -Os
-	# https://github.com/kaniini/libucontext/issues/52
-	CFLAGS="$CFLAGS -O2"
-
 	make ARCH="$LIBUCONTEXT_ARCH"
 	make ARCH="$LIBUCONTEXT_ARCH" docs
 }
@@ -35,4 +32,5 @@ package() {
 
 sha512sums="
 6603f2dcd87c4d9919c1726f2964632483e1a647733ff543d5935e3e2dac548adf320f1f9fb4c494691fe99fb393d64b15369f04d3783b2ca4c40b68c3d87865  libucontext-1.2.tar.xz
+4e797976943dcc98dbc2541a17e517da1b95ed50e0c730c547ccc604e682d1150e90c6bb29f601549b6a0bf4b7228e7a7d9883e97ea6bff4d12956df6b9a1195  0001-common-trampoline-Ensure-omission-of-frame-pointer.patch
 "