libucontext: Add package

Description (from libucontext github page):
libucontext (https://https://github.com/kaniini/libucontext) is a
library which provides the ucontext.h C API. Unlike other
implementations, it faithfully follows the kernel process ABI when
doing context swaps. libucontext is used on almost all musl
distributions to provide the legacy ucontext.h API.

This package is meant as a development package. There is no need
to install a package on the router if an application or library
is linked against the static libraries. Though, shared libraries
are provided also.

It is used to link libraries/applications against it which need the
system calls

* makecontext
* swapcontext
* getcontext
* setcontext

E.g. the asynchronous API of libmariadb (c-connector) uses this
system calls. Because libmusl didn't provide that system calls this
synchronous API is currently (without libucontexe) not working - it
segfaults.

Co-developed-by: Tianling Shen <cnsztl@immortalwrt.org>
Signed-off-by: Tianling Shen <cnsztl@immortalwrt.org>
Signed-off-by: Volker Christian <me@vchrist.at>

libs/libucontext/Makefile

@@ -0,0 +1,62 @@
+include $(TOPDIR)/rules.mk
+
+PKG_NAME:=libucontext
+PKG_VERSION:=1.2
+PKG_RELEASE:=1
+
+PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
+PKG_SOURCE_URL:=https://codeload.github.com/kaniini/libucontext/tar.gz/v$(PKG_VERSION)?
+PKG_HASH:=2657e087c493263e7bbbde152a5bc08ce22dc5a7970887ac4fd251b90b58401f
+
+PKG_MAINTAINER:=Volker Christian <me@vchrist.at>
+PKG_LICENSE:=ISC
+PKG_LICENSE_FILES:=LICENSE
+
+PKG_BUILD_FLAGS:=no-mips16
+PKG_BUILD_PARALLEL:=1
+PKG_INSTALL:=1
+
+include $(INCLUDE_DIR)/package.mk
+include $(INCLUDE_DIR)/meson.mk
+
+define Package/libucontext
+  SECTION:=libs
+  CATEGORY:=Libraries
+  TITLE:=libucontext is a library which provides the ucontext.h C API
+  URL:=https://github.com/kaniini/libucontext
+  DEPENDS:=@USE_MUSL
+endef
+
+define Package/libucontext-tests
+  SECTION:=utils
+  CATEGORY:=Utilities
+  TITLE:=Test applications for libucontext
+  URL:=https://github.com/kaniini/libucontext
+  DEPENDS:=libucontext
+endef
+
+define Package/libucontext/description
+  Thie package is a development package aimed to be linked to
+  libraries/applications which need the SYS-V ucontext API.
+endef
+
+define Build/InstallDev
+	$(INSTALL_DIR) $(1)/usr/include $(1)/usr/lib/pkgconfig
+	$(CP) $(PKG_INSTALL_DIR)/usr/include/libucontext $(1)/usr/include/
+	$(CP) $(PKG_INSTALL_DIR)/usr/lib/libucontext* $(1)/usr/lib/
+	$(CP) $(PKG_INSTALL_DIR)/usr/lib/pkgconfig/libucontext.pc $(1)/usr/lib/pkgconfig/
+endef
+
+define Package/libucontext/install
+	$(INSTALL_DIR) $(1)/usr/lib
+	$(CP) $(PKG_INSTALL_DIR)/usr/lib/libucontext*.so.* $(1)/usr/lib/
+endef
+
+define Package/libucontext-tests/install
+	$(INSTALL_DIR) $(1)/usr/bin
+	$(INSTALL_BIN) $(MESON_BUILD_DIR)/test_libucontext_posix $(1)/usr/bin/
+	$(INSTALL_BIN) $(MESON_BUILD_DIR)/test_libucontext $(1)/usr/bin/
+endef
+
+$(eval $(call BuildPackage,libucontext))
+$(eval $(call BuildPackage,libucontext-tests))

libs/libucontext/patches/010-return_values_fix.patch

@@ -0,0 +1,17 @@
+--- a/arch/arm/swapcontext.S
++++ b/arch/arm/swapcontext.S
+@@ -17,10 +17,12 @@ ALIAS(__swapcontext, libucontext_swapcon
+ 
+ FUNC(libucontext_swapcontext)
+ 	/* copy all of the current registers into the ucontext structure */
+-	add	r2, r0, #REG_OFFSET(0)
+-	stmia	r2, {r0-r12}
+ 	str	r13, [r0,#REG_OFFSET(13)]
+ 	str	r14, [r0,#REG_OFFSET(15)]
++	add	r2, r0, #REG_OFFSET(0)
++	/* copy r0 with value 0 to indicate success (return value 0) */
++	mov r0, #0
++	stmia	r2, {r0-r12}
+ 
+ 	/* load new registers from the second ucontext structure */
+ 	add	r14, r1, #REG_OFFSET(0)

libs/libucontext/patches/020-honor_return_values_fix.patch

@@ -0,0 +1,122 @@
+--- a/test_libucontext.c
++++ b/test_libucontext.c
+@@ -9,6 +9,9 @@
+ #include <string.h>
+ #include <libucontext/libucontext.h>
+ 
++#define handle_error(msg) \
++           do { perror(msg); exit(EXIT_FAILURE); } while (0)
++
+ static libucontext_ucontext_t ctx[3];
+ 
+ 
+@@ -36,7 +39,8 @@ static void f1 (int a, int b, int c, int
+ 	printf("looks like all arguments are passed correctly\n");
+ 
+ 	printf("swap back to f2\n");
+-	libucontext_swapcontext(&ctx[1], &ctx[2]);
++	if (libucontext_swapcontext(&ctx[1], &ctx[2]) != 0)
++		handle_error("libucontext_swapcontext");
+ 	printf("finish f1\n");
+ }
+ 
+@@ -44,7 +48,8 @@ static void f1 (int a, int b, int c, int
+ static void f2 (void) {
+ 	printf("start f2\n");
+ 	printf("swap to f1\n");
+-	libucontext_swapcontext(&ctx[2], &ctx[1]);
++	if (libucontext_swapcontext(&ctx[2], &ctx[1]) != 0)
++		handle_error("libucontext_swapcontext");
+ 	printf("finish f2, should swap to f1\n");
+ }
+ 
+@@ -63,7 +68,8 @@ int main (int argc, const char *argv[])
+ 	printf("setting up context 1\n");
+ 
+ 
+-	libucontext_getcontext(&ctx[1]);
++	if (libucontext_getcontext(&ctx[1]) != 0)
++		handle_error("libucontext_getcontext");
+ 	ctx[1].uc_stack.ss_sp = st1;
+ 	ctx[1].uc_stack.ss_size = sizeof st1;
+ 	ctx[1].uc_link = &ctx[0];
+@@ -83,16 +89,20 @@ int main (int argc, const char *argv[])
+ 	printf("doing initial swapcontext\n");
+ 
+ 
+-	libucontext_swapcontext(&ctx[0], &ctx[2]);
++	if (libucontext_swapcontext(&ctx[0], &ctx[2]) != 0)
++		handle_error("libucontext_swapcontext");
+ 
+ 
+ 	printf("returned from initial swapcontext\n");
+ 
+ 
+ 	/* test ability to use getcontext/setcontext without makecontext */
+-	libucontext_getcontext(&ctx[1]);
++	if (libucontext_getcontext(&ctx[1]) != 0)
++		handle_error("libucontext_getcontext");
+ 	printf("done = %d\n", done);
+-	if (done++ == 0) libucontext_setcontext(&ctx[1]);
++	if (done++ == 0)
++		if (libucontext_setcontext(&ctx[1]) != 0)
++			handle_error("libucontext_setcontext");
+ 	if (done != 2) {
+ 		fprintf(stderr, "wrong value for done.  got %d, expected 2\n", done);
+ 		abort();
+--- a/test_libucontext_posix.c
++++ b/test_libucontext_posix.c
+@@ -9,6 +9,9 @@
+ #include <string.h>
+ #include <ucontext.h>
+ 
++#define handle_error(msg) \
++           do { perror(msg); exit(EXIT_FAILURE); } while (0)
++
+ static ucontext_t ctx[3];
+ 
+ 
+@@ -36,7 +39,8 @@ static void f1 (int a, int b, int c, int
+ 	printf("looks like all arguments are passed correctly\n");
+ 
+ 	printf("swap back to f2\n");
+-	swapcontext(&ctx[1], &ctx[2]);
++	if (swapcontext(&ctx[1], &ctx[2]) != 0)
++		handle_error("swapcontext");
+ 	printf("finish f1\n");
+ }
+ 
+@@ -44,7 +48,8 @@ static void f1 (int a, int b, int c, int
+ static void f2 (void) {
+ 	printf("start f2\n");
+ 	printf("swap to f1\n");
+-	swapcontext(&ctx[2], &ctx[1]);
++	if (swapcontext(&ctx[2], &ctx[1]) != 0)
++		handle_error("swapcontext");
+ 	printf("finish f2, should swap to f1\n");
+ }
+ 
+@@ -83,16 +88,19 @@ int main (int argc, const char *argv[])
+ 	printf("doing initial swapcontext\n");
+ 
+ 
+-	swapcontext(&ctx[0], &ctx[2]);
+-
++	if (swapcontext(&ctx[0], &ctx[2]) != 0)
++		handle_error("swapcontext");
+ 
+ 	printf("returned from initial swapcontext\n");
+ 
+ 
+ 	/* test ability to use getcontext/setcontext without makecontext */
+-	getcontext(&ctx[1]);
++	if (getcontext(&ctx[1]) != 0)
++		handle_error("getcontext");
+ 	printf("done = %d\n", done);
+-	if (done++ == 0) setcontext(&ctx[1]);
++	if (done++ == 0)
++		if (setcontext(&ctx[1]) != 0)
++			handle_error("setcontext");
+ 	if (done != 2) {
+ 		fprintf(stderr, "wrong value for done.  got %d, expected 2\n", done);
+ 		abort();