um: allow static linking for non-glibc libc implementations

Changes from v2:
* rebased to accomodate b816b3db15f68690ee72a4a414624f8e82942b25 ("kbuild: fix CONFIG_CC_CAN_LINK(_STATIC) for cross-compilation with Clang")
* removed unused FORBID_STATIC_LINK config option
* cc-ed Masahiro Yamada <[email protected]> for can-link.sh approve

This is a continuation of [1]. Since I was able to produce a working UML binary with UML_NET_VECTOR linked with musl with the changes included in the patches here. I was compiling on Arch Linux, so hopefully all the latest versions of the compiler, libraries and binutils.

I also tested allyesconfig with both musl and glibc. The compilation succeeds with both, however both binaries (glibc one being dynamically linked) segfault on start. This is probably of some incompatible config option/module being included and not related to musl/glibc.

[1]: https://patchwork.ozlabs.org/project/linux-um/patch/[email protected]/

Ignat Korchagin (3):
um/kconfig: introduce CC_CAN_LINK_STATIC_NO_RUNTIME_DEPS
um: some fixes to build UML with musl
um: allow static linking for non-glibc implementations

 arch/um/Kconfig               |  5 +----
 arch/um/drivers/Kconfig       |  3 ---
 arch/um/drivers/daemon_user.c |  1 +
 arch/um/drivers/pcap_user.c   | 12 ++++++------
 arch/um/drivers/slip_user.c   |  2 +-
 arch/um/drivers/vector_user.c |  4 +---
 arch/um/os-Linux/util.c       |  2 +-
 arch/x86/um/user-offsets.c    |  2 +-
 init/Kconfig                  |  6 ++++++
 scripts/cc-can-link.sh        |  5 +++--
 10 files changed, 21 insertions(+), 21 deletions(-)

2.20.1


_______________________________________________
linux-um mailing list
[email protected]
http://lists.infradead.org/mailman/listinfo/linux-um

For statically linked UML build it is important to take into account the standard C-library implementation. Some implementations, notably glibc have
caveats: even when linked statically, the final program might require some runtime dependencies, if certain functions are used within the code.

Consider the following program:
int main(void)

{
	getpwent();
	return 0;
}

Compiling this program and linking statically with glibc produces the following warning from the linker:
/usr/sbin/ld: /tmp/ccuthw1o.o: in function `main':
test.c:(.text+0x5): warning: Using 'getpwent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking

We will use the flag to detect such C-library implementation build time and possibly disable static linking for UML to avoid producing a binary with unexpected behaviour and dependencies.

---
 init/Kconfig           | 6 ++++++
 scripts/cc-can-link.sh | 5 +++--
 2 files changed, 9 insertions(+), 2 deletions(-)

index 0498af567f70..0a1ec56c9f33 100644
@@ -57,6 +57,12 @@ config CC_CAN_LINK_STATIC
 	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag) -static) if 64BIT
 	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag) -static)
 
+config CC_CAN_LINK_STATIC_NO_RUNTIME_DEPS
+	bool
+	depends on UML && CC_CAN_LINK_STATIC
+	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag) -static -Xlinker --fatal-warnings) if 64BIT
+	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag) -static -Xlinker --fatal-warnings)
+
 config CC_HAS_ASM_GOTO
 	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
 

index 6efcead31989..e5011a46103e 100755
@@ -2,10 +2,11 @@
 # SPDX-License-Identifier: GPL-2.0
 
 cat << "END" | $@ -x c - -o /dev/null >/dev/null 2>&1
-#include <stdio.h>
+#include <sys/types.h>
+#include <pwd.h>
 int main(void)
 {
-	printf("");
+	getpwent();
 	return 0;
 }
 END

2.20.1


_______________________________________________
linux-um mailing list
[email protected]
http://lists.infradead.org/mailman/listinfo/linux-um

musl toolchain and headers are a bit more strict. These fixes enable building UML with musl as well as seem not to break on glibc.

---
 arch/um/drivers/daemon_user.c |  1 +
 arch/um/drivers/pcap_user.c   | 12 ++++++------
 arch/um/drivers/slip_user.c   |  2 +-
 arch/um/drivers/vector_user.c |  4 +---
 arch/um/os-Linux/util.c       |  2 +-
 arch/x86/um/user-offsets.c    |  2 +-
 6 files changed, 11 insertions(+), 12 deletions(-)

index 3695821d06a2..785baedc3555 100644
@@ -7,6 +7,7 @@
  */
 
 #include <stdint.h>
+#include <string.h>
 #include <unistd.h>
 #include <errno.h>
 #include <sys/types.h>

index bbd20638788a..52ddda3e3b10 100644
@@ -32,7 +32,7 @@ static int pcap_user_init(void *data, void *dev)
 	return 0;
 }
 
-static int pcap_open(void *data)
+static int pcap_user_open(void *data)
 {
 	struct pcap_data *pri = data;
 	__u32 netmask;

@@ -44,14 +44,14 @@ static int pcap_open(void *data)
 	if (pri->filter != NULL) {
 		err = dev_netmask(pri->dev, &netmask);
 		if (err < 0) {
-			printk(UM_KERN_ERR "pcap_open : dev_netmask failed\n");
+			printk(UM_KERN_ERR "pcap_user_open : dev_netmask failed\n");
 			return -EIO;
 		}
 
 		pri->compiled = uml_kmalloc(sizeof(struct bpf_program),
 					UM_GFP_KERNEL);
 		if (pri->compiled == NULL) {
-			printk(UM_KERN_ERR "pcap_open : kmalloc failed\n");
+			printk(UM_KERN_ERR "pcap_user_open : kmalloc failed\n");
 			return -ENOMEM;
 		}
 

@@ -59,14 +59,14 @@ static int pcap_open(void *data)
 				   (struct bpf_program *) pri->compiled,
 				   pri->filter, pri->optimize, netmask);
 		if (err < 0) {
-			printk(UM_KERN_ERR "pcap_open : pcap_compile failed - "
+			printk(UM_KERN_ERR "pcap_user_open : pcap_compile failed - "
 			       "'%s'\n", pcap_geterr(pri->pcap));
 			goto out;
 		}
 
 		err = pcap_setfilter(pri->pcap, pri->compiled);
 		if (err < 0) {
-			printk(UM_KERN_ERR "pcap_open : pcap_setfilter "
+			printk(UM_KERN_ERR "pcap_user_open : pcap_setfilter "
 			       "failed - '%s'\n", pcap_geterr(pri->pcap));
 			goto out;
 		}

@@ -127,7 +127,7 @@ int pcap_user_read(int fd, void *buffer, int len, struct pcap_data *pri)
 
 const struct net_user_info pcap_user_info = {
 	.init		= pcap_user_init,
-	.open		= pcap_open,
+	.open		= pcap_user_open,
 	.close	 	= NULL,
 	.remove	 	= pcap_remove,
 	.add_address	= NULL,

index 8016d32b6809..482a19c5105c 100644
@@ -9,7 +9,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <string.h>
-#include <sys/termios.h>
+#include <termios.h>
 #include <sys/wait.h>
 #include <net_user.h>
 #include <os.h>

index c4a0f26b2824..45d4164ad355 100644
@@ -18,9 +18,7 @@
 #include <fcntl.h>
 #include <sys/socket.h>
 #include <sys/un.h>
-#include <net/ethernet.h>
 #include <netinet/ip.h>
-#include <netinet/ether.h>
 #include <linux/if_ether.h>
 #include <linux/if_packet.h>
 #include <sys/wait.h>

@@ -332,7 +330,7 @@ static struct vector_fds *user_init_unix_fds(struct arglist *ifspec, int id)
 	}
 	switch (id) {
 	case ID_BESS:
-		if (connect(fd, remote_addr, sizeof(struct sockaddr_un)) < 0) {
+		if (connect(fd, (const struct sockaddr *) remote_addr, sizeof(struct sockaddr_un)) < 0) {
 			printk(UM_KERN_ERR "bess open:cannot connect to %s %i", remote_addr->sun_path, -errno);
 			goto unix_cleanup;
 		}

index ecf2f390fad2..07327425d06e 100644
@@ -10,7 +10,7 @@
 #include <signal.h>
 #include <string.h>
 #include <termios.h>
-#include <wait.h>
+#include <sys/wait.h>
 #include <sys/mman.h>
 #include <sys/utsname.h>
 #include <init.h>

index c51dd8363d25..bae61554abcc 100644
@@ -2,7 +2,7 @@
 #include <stdio.h>
 #include <stddef.h>
 #include <signal.h>
-#include <sys/poll.h>
+#include <poll.h>
 #include <sys/mman.h>
 #include <sys/user.h>
 #define __FRAME_OFFSETS

2.20.1


_______________________________________________
linux-um mailing list
[email protected]
http://lists.infradead.org/mailman/listinfo/linux-um

It is possible to produce a statically linked UML binary with UML_NET_VECTOR, UML_NET_VDE and UML_NET_PCAP options enabled using alternative libc implementations, which do not rely on NSS, such as musl.

Allow static linking in this case.

---
 arch/um/Kconfig         | 5 +----
 arch/um/drivers/Kconfig | 3 ---
 2 files changed, 1 insertion(+), 7 deletions(-)

index 9318dc6d1a0c..beb98b3b9f75 100644
@@ -62,12 +62,9 @@ config NR_CPUS
 
 source "arch/$(HEADER_ARCH)/um/Kconfig"
 
-config FORBID_STATIC_LINK
-	bool
-
 config STATIC_LINK
 	bool "Force a static link"
-	depends on !FORBID_STATIC_LINK
+	depends on CC_CAN_LINK_STATIC_NO_RUNTIME_DEPS || (!UML_NET_VECTOR && !UML_NET_VDE && !UML_NET_PCAP)
 	help
 	  This option gives you the ability to force a static link of UML.
 	  Normally, UML is linked as a shared binary.  This is inconvenient for

index 9160ead56e33..72d417055782 100644
@@ -234,7 +234,6 @@ config UML_NET_DAEMON
 config UML_NET_VECTOR
 	bool "Vector I/O high performance network devices"
 	depends on UML_NET
-	select FORBID_STATIC_LINK
 	help
 	This User-Mode Linux network driver uses multi-message send
 	and receive functions. The host running the UML guest must have

@@ -246,7 +245,6 @@ config UML_NET_VECTOR
 config UML_NET_VDE
 	bool "VDE transport (obsolete)"
 	depends on UML_NET
-	select FORBID_STATIC_LINK
 	help
 	This User-Mode Linux network transport allows one or more running
 	UMLs on a single host to communicate with each other and also

@@ -294,7 +292,6 @@ config UML_NET_MCAST
 config UML_NET_PCAP
 	bool "pcap transport (obsolete)"
 	depends on UML_NET
-	select FORBID_STATIC_LINK
 	help
 	The pcap transport makes a pcap packet stream on the host look
 	like an ethernet device inside UML.  This is useful for making

2.20.1


_______________________________________________
linux-um mailing list
[email protected]
http://lists.infradead.org/mailman/listinfo/linux-um

Yes, makes sense. I've shortened it to MAY_HAVE_RUNTIME_DEPS and reposted the series.

_______________________________________________
linux-um mailing list
[email protected]
http://lists.infradead.org/mailman/listinfo/linux-um