Merge branch 'patch-4' into 'master'

New kernel compatibility; obstack; pthread_getname_np

The gcompat loader compiled as a static binary doesn't work on Linux since [a4ff8e8620d3f4](https://github.com/torvalds/linux/commit/a4ff8e8620d3f4f50ac4b41e8067b7d395056843), failing with an error like:
```
[349055.473655] 13325 (cmake): Uhuuh, elf segment at 0000000000400000 requested but the memory is mapped already
```
This is because the actual binary we want to run is also loaded at 0x400000. While it's actually okay to overlap the binary, since we're going to call `execve` again, the kernel doesn't allow the overlap anymore. Fix that by compiling the loader as static PIE, so it can be put at a different address.

Also add `pthread_getname_np` and the option to link `obstack`.

See merge request !4

6 files changed, 71 insertions, 23 deletions

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 7c5365c..c494a38 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -11,6 +11,17 @@
 0.4.0 (201?-??-??)
 ==================
 
+Build system
+------------
+
+* Allow building against libobstack.
+* Fix compatibility with Linux 4.17 and newer.
+
+pthread
+-------
+
+* Add pthread_getname_np.
+
 wchar
 -----
 
diff --git a/Makefile b/Makefile
index 934422f..6a36129 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,6 @@
 LIBGCOMPAT_INCLUDE = \
-	libgcompat/alias.h
+	libgcompat/alias.h \
+	libgcompat/internal.h
 LIBGCOMPAT_SRC = \
 	libgcompat/ctype.c		\
 	libgcompat/cxx_thread.c		\
@@ -43,36 +44,50 @@ LOADER_OBJ = ${LOADER_SRC:.c=.o}
 LOADER_NAME = ld-linux.so.2
 LOADER_PATH = /lib/${LOADER_NAME}
 
-ifdef WITH_LIBUCONTEXT
+PKG_CONFIG ?= pkg-config
 
-LIBUCONTEXT_LIBS   = -Wl,--no-as-needed -lucontext
+ifdef WITH_LIBUCONTEXT
 LIBUCONTEXT_CFLAGS = -DWITH_LIBUCONTEXT
+LIBUCONTEXT_LIBS   = -lucontext
+endif
+
+ifndef WITH_OBSTACK
+WITH_OBSTACK = $(shell \
+  for pkg in obstack obstack-standalone; do \
+    ${PKG_CONFIG} --exists "$$pkg" && { echo "$$pkg"; exit 0; } \
+  done; echo "no")
+endif
 
+ifneq (${WITH_OBSTACK},no)
+OBSTACK_CFLAGS = $(shell ${PKG_CONFIG} --cflags ${WITH_OBSTACK}) -DWITH_OBSTACK
+OBSTACK_LIBS   = $(shell ${PKG_CONFIG} --libs ${WITH_OBSTACK})
 endif
 
 all: ${LIBGCOMPAT_NAME} ${LOADER_NAME}
 
 ${LIBGCOMPAT_NAME}: ${LIBGCOMPAT_OBJ}
-	$(CC) -o ${LIBGCOMPAT_NAME} -Wl,-soname,${LIBGCOMPAT_NAME} \
-		-shared ${LIBGCOMPAT_OBJ} ${LIBUCONTEXT_LIBS}
+	${CC} ${CFLAGS} ${LDFLAGS} -shared -Wl,-soname,${LIBGCOMPAT_NAME} \
+		-o ${LIBGCOMPAT_NAME} ${LIBGCOMPAT_OBJ} \
+		-Wl,--no-as-needed ${LIBUCONTEXT_LIBS} ${OBSTACK_LIBS}
 
 ${LIBGCOMPAT_OBJ}: ${LIBGCOMPAT_INCLUDE}
 
 ${LOADER_NAME}: ${LOADER_OBJ}
-	$(CC) -o ${LOADER_NAME} -fPIE -static ${LOADER_OBJ}
+	${CC} ${CFLAGS} ${LDFLAGS} -static-pie -o ${LOADER_NAME} ${LOADER_OBJ}
 
 .c.o:
-	$(CC) -c -D_BSD_SOURCE -DLIBGCOMPAT=\"${LIBGCOMPAT_PATH}\" \
-		-DLINKER=\"${LINKER_PATH}\" -DLOADER=\"${LOADER_NAME}\" \
-		-Ilibgcompat ${LIBUCONTEXT_CFLAGS} \
-		-fPIC -std=c99 -Wall -Wextra -Wno-frame-address \
-		-Wno-unused-parameter ${CFLAGS} ${CPPFLAGS} -o $@ $<
+	${CC} ${CPPFLAGS} ${CFLAGS} -c -D_BSD_SOURCE \
+		-DLIBGCOMPAT='"${LIBGCOMPAT_PATH}"' \
+		-DLINKER='"${LINKER_PATH}"' -DLOADER='"${LOADER_NAME}"' \
+		-fPIC -Ilibgcompat -std=c99 \
+		-Wall -Wextra -Wno-frame-address -Wno-unused-parameter \
+		${LIBUCONTEXT_CFLAGS} ${OBSTACK_CFLAGS} -o $@ $<
 
 clean:
 	rm -f libgcompat/*.o loader/*.o ${LIBGCOMPAT_NAME} ${LOADER_NAME}
 
 format:
-	clang-format -i ${LIBGCOMPAT_SRC} ${LOADER_SRC}
+	clang-format -i ${LIBGCOMPAT_INCLUDE} ${LIBGCOMPAT_SRC} ${LOADER_SRC}
 
 install: all
 	install -D -m755 ${LIBGCOMPAT_NAME} ${DESTDIR}/${LIBGCOMPAT_PATH}
diff --git a/libgcompat/alias.h b/libgcompat/alias.h
index 3f54672..bb99690 100644
--- a/libgcompat/alias.h
+++ b/libgcompat/alias.h
@@ -1,9 +1,9 @@
 #ifndef _ALIAS_H_
 #define _ALIAS_H_
 
-#define alias(old, new) \
+#define alias(old, new)                                                        \
 	extern __typeof(old) new __attribute__((__alias__(#old)))
-#define weak_alias(old, new) \
+#define weak_alias(old, new)                                                   \
 	extern __typeof(old) new __attribute__((weak, __alias__(#old)))
 
 #endif /* _ALIAS_H_ */
diff --git a/libgcompat/internal.h b/libgcompat/internal.h
index 3b08271..a246547 100644
--- a/libgcompat/internal.h
+++ b/libgcompat/internal.h
@@ -3,12 +3,11 @@
 
 void GCOMPAT__panic(const char *fmt, ...) __attribute__((noreturn));
 
-#define GCOMPAT__assert_with_reason(chk, ...)			\
-	do {							\
-		if (!(chk)) {					\
-			GCOMPAT__panic(__VA_ARGS__);		\
-		}						\
-	}							\
-	while(0);
+#define GCOMPAT__assert_with_reason(chk, ...)                                  \
+	do {                                                                   \
+		if (!(chk)) {                                                  \
+			GCOMPAT__panic(__VA_ARGS__);                           \
+		}                                                              \
+	} while (0);
 
 #endif
diff --git a/libgcompat/pthread.c b/libgcompat/pthread.c
index 4ebbe6b..0456c40 100644
--- a/libgcompat/pthread.c
+++ b/libgcompat/pthread.c
@@ -1,4 +1,8 @@
-#include <pthread.h>
+#define _GNU_SOURCE
+#include <errno.h>   /* errno */
+#include <fcntl.h>   /* O_CLOEXEC, O_RDONLY */
+#include <pthread.h> /* pthread_atfork */
+#include <unistd.h>  /* open, read */
 
 #include "alias.h" /* weak_alias */
 
@@ -27,3 +31,22 @@ int __register_atfork(void (*prepare)(void), void (*parent)(void),
 	return pthread_atfork(prepare, parent, child);
 }
 weak_alias(__register_atfork, register_atfork);
+
+/**
+ * Get the name of a thread.
+ */
+int pthread_getname_np(pthread_t thread, char *name, size_t len)
+{
+	int fd = open("/proc/thread-self/comm", O_RDONLY | O_CLOEXEC);
+	char dummy;
+
+	if (fd < 0)
+		return errno;
+	if (read(fd, name, len) < 0)
+		return errno;
+	/* If there's more to read, the buffer was too small. */
+	if (read(fd, &dummy, 1) > 0)
+		return ERANGE;
+
+	return 0;
+}
diff --git a/libgcompat/wchar.c b/libgcompat/wchar.c
index 823c3e3..c60963e 100644
--- a/libgcompat/wchar.c
+++ b/libgcompat/wchar.c
@@ -45,7 +45,7 @@ int __vswprintf_chk(wchar_t *s, size_t n, int flag, size_t slen,
  * LSB 5.0: LSB-Core-generic/baselib---wcstol-internal-1.html
  */
 long int __wcstol_internal(const wchar_t *nptr, wchar_t **endptr, int base,
-			   int group)
+                           int group)
 {
 	assert(group == 0);
 	return wcstol(nptr, endptr, base);