system/libucontext: Fix segfault on pmmx

Revert a commit that uses the common trampoline.
TODO: report upstream.

system/libucontext/APKBUILD

@@ -9,7 +9,9 @@ license="ISC"
 depends=""
 makedepends=""
 subpackages="$pkgname-dev"
-source="https://distfiles.dereferenced.org/libucontext/libucontext-$pkgver.tar.xz"
+source="https://distfiles.dereferenced.org/libucontext/libucontext-$pkgver.tar.xz
+	pmmx.patch
+	"
 
 case "$CTARGET_ARCH" in
 aarch64_be)	LIBUCONTEXT_ARCH="aarch64" ;;
@@ -31,4 +33,5 @@ package() {
 	make ARCH="$LIBUCONTEXT_ARCH" DESTDIR="$pkgdir" install
 }
 
-sha512sums="6603f2dcd87c4d9919c1726f2964632483e1a647733ff543d5935e3e2dac548adf320f1f9fb4c494691fe99fb393d64b15369f04d3783b2ca4c40b68c3d87865  libucontext-1.2.tar.xz"
+sha512sums="6603f2dcd87c4d9919c1726f2964632483e1a647733ff543d5935e3e2dac548adf320f1f9fb4c494691fe99fb393d64b15369f04d3783b2ca4c40b68c3d87865  libucontext-1.2.tar.xz
+e5855aaf5042856e019dcd8bbf85c1319c4ed3ea836fd64617595b1fcacc14a101f7631e9d07a8af7f624a82c59a5bc6d2c1011b961ba4fede37725b6f5e9c37  pmmx.patch"

system/libucontext/pmmx.patch

+From 196db62779287efb098943c2d4f2433e4b8ea592 Mon Sep 17 00:00:00 2001
+From: "A. Wilcox" <AWilcox@Wilcox-Tech.com>
+Date: Mon, 25 Apr 2022 23:34:32 -0500
+Subject: [PATCH] Revert "x86: port to use common trampoline"
+
+This reverts commit 388edbe12138e8300e230e2bc9c08a8f273e98d9.
+---
+ arch/x86/defs.h         |  3 ---
+ arch/x86/startcontext.S | 41 +++++++++++++++++++++++++++++++++++++++++
+ arch/x86/trampoline.c   |  3 ---
+ 3 files changed, 41 insertions(+), 6 deletions(-)
+ create mode 100644 arch/x86/startcontext.S
+ delete mode 100644 arch/x86/trampoline.c
+
+diff --git a/arch/x86/defs.h b/arch/x86/defs.h
+index 9370869..e0166e5 100644
+--- a/arch/x86/defs.h
++++ b/arch/x86/defs.h
+@@ -57,9 +57,6 @@
+ 
+ #define MCONTEXT_GREGS	(20)
+ 
+-#define FETCH_LINKPTR(dest) \
+-	asm("movl (%%esp, %%ebx, 4), %0" : "=r" ((dest)));
+-
+ #include "common-defs.h"
+ 
+ #endif
+diff --git a/arch/x86/startcontext.S b/arch/x86/startcontext.S
+new file mode 100644
+index 0000000..1cbc68c
+--- /dev/null
++++ b/arch/x86/startcontext.S
+@@ -0,0 +1,41 @@
++/*
++ * Copyright (c) 2018, 2020 Ariadne Conill <ariadne@dereferenced.org>
++ *
++ * Permission to use, copy, modify, and/or distribute this software for any
++ * purpose with or without fee is hereby granted, provided that the above
++ * copyright notice and this permission notice appear in all copies.
++ *
++ * This software is provided 'as is' and without any warranty, express or
++ * implied.  In no event shall the authors be liable for any damages arising
++ * from the use of this software.
++ */
++
++#include "defs.h"
++
++FUNC(libucontext_trampoline)
++	/* get the proper context into position and test for NULL */
++	leal	(%esp,%ebx,4), %esp
++	cmpl	$0, (%esp)
++
++	/* restore global offset table, exit@plt and libucontext_setcontext@plt need this */
++	call	__i686.get_pc_thunk.bx
++	addl	$_GLOBAL_OFFSET_TABLE_, %ebx
++
++	/* if we have no linked context, lets get out of here */
++	je	no_linked_context
++
++	/* call setcontext to switch to the linked context */
++	call	libucontext_setcontext@plt
++	movl	%eax, (%esp)
++
++no_linked_context:
++	/* we are returning into a null context, it seems, so maybe we should exit */
++	call	exit@plt
++
++	/* something is really hosed, call hlt to force termination */
++	hlt
++
++__i686.get_pc_thunk.bx:
++	mov	(%esp), %ebx
++	ret
++END(libucontext_trampoline)
+diff --git a/arch/x86/trampoline.c b/arch/x86/trampoline.c
+deleted file mode 100644
+index 699a050..0000000
+--- a/arch/x86/trampoline.c
++++ /dev/null
+@@ -1,3 +0,0 @@
+-#include "defs.h"
+-#include <libucontext/libucontext.h>
+-#include "common-trampoline.c"
+-- 
+2.32.0 (Apple Git-132)
+