From a9ca51afd2b9f68f57de3a4c3d962d1d763572ca Mon Sep 17 00:00:00 2001 From: Alexander Miller Date: Thu, 28 Nov 2019 22:17:24 +0100 Subject: [PATCH] Better supported way to set symbol versions for legacy syscalls Using a linker script to set a symbol versions is an undocumented hack and doesn't work reliably in many cases. It works (to some degree) with the bfd linker, but fails with gold or lld. And even with bfd it can break when using --gc-sections or LTO. The result may be a library where the code has been discarded and the versioned symbols are unusable, e.g. 23: 00000000 0 NOTYPE GLOBAL DEFAULT ABS getxattr@ATTR_1.0 instead of 23: 000033c0 0 FUNC GLOBAL DEFAULT 11 getxattr@ATTR_1.0 Remove the linker script entirely and set symbol versions with the symver attribute if available (in gcc >= 10, but not in clang), otherwise use the traditional global asm solution with a .symver directive. Those are the documented ways to do it and well supported by (almost) all configurations. (The exception is old gcc with LTO; a workaround is included, but some versions may still need -flto-partition=none). Signed-off-by: Alexander Miller --- libattr/Makemodule.am | 5 +---- libattr/libattr.lds | 12 ------------ libattr/syscalls.c | 33 +++++++++++++++++++++++++++++++++ 3 files changed, 34 insertions(+), 16 deletions(-) delete mode 100644 libattr/libattr.lds diff --git a/libattr/Makemodule.am b/libattr/Makemodule.am index 4b3720c..e9f5661 100644 --- a/libattr/Makemodule.am +++ b/libattr/Makemodule.am @@ -8,7 +8,7 @@ LT_CURRENT = 2 LT_AGE = 1 LTVERSION = $(LT_CURRENT):$(LT_REVISION):$(LT_AGE) -libattr_la_DEPENDENCIES = exports libattr/libattr.lds +libattr_la_DEPENDENCIES = exports libattr_la_SOURCES = \ libattr/attr_copy_action.c \ libattr/attr_copy_check.c \ @@ -20,7 +20,4 @@ libattr_la_SOURCES = \ libattr_la_CFLAGS = -include libattr/libattr.h libattr_la_LDFLAGS = \ -Wl,--version-script,$(top_srcdir)/exports \ - -Wl,$(top_srcdir)/libattr/libattr.lds \ -version-info $(LTVERSION) - -EXTRA_DIST += libattr/libattr.lds diff --git a/libattr/libattr.lds b/libattr/libattr.lds deleted file mode 100644 index 947f15d..0000000 --- a/libattr/libattr.lds +++ /dev/null @@ -1,12 +0,0 @@ -"fgetxattr@ATTR_1.0" = libattr_fgetxattr; -"flistxattr@ATTR_1.0" = libattr_flistxattr; -"fremovexattr@ATTR_1.0" = libattr_fremovexattr; -"fsetxattr@ATTR_1.0" = libattr_fsetxattr; -"getxattr@ATTR_1.0" = libattr_getxattr; -"lgetxattr@ATTR_1.0" = libattr_lgetxattr; -"listxattr@ATTR_1.0" = libattr_listxattr; -"llistxattr@ATTR_1.0" = libattr_llistxattr; -"lremovexattr@ATTR_1.0" = libattr_lremovexattr; -"lsetxattr@ATTR_1.0" = libattr_lsetxattr; -"removexattr@ATTR_1.0" = libattr_removexattr; -"setxattr@ATTR_1.0" = libattr_setxattr; diff --git a/libattr/syscalls.c b/libattr/syscalls.c index 721ad7f..1f5fd7a 100644 --- a/libattr/syscalls.c +++ b/libattr/syscalls.c @@ -26,6 +26,27 @@ #include #include +/* + * Versioning of compat symbols: + * prefer symver attribute if available (since gcc 10), + * fall back to traditional .symver asm directive otherwise. + */ +#ifdef __has_attribute +# if __has_attribute(symver) +# define SYMVER(cn, vn) __typeof(cn) cn __attribute__((symver(vn))) +# elif __has_attribute(no_reorder) + /* + * Avoid wrong partitioning with older gcc and LTO. May not work reliably + * with all versions; use -flto-partition=none if you encounter problems. + */ +# define SYMVER(cn, vn) __typeof(cn) cn __attribute__((noreorder)); \ + __asm__(".symver " #cn "," vn) +# endif +#endif +#ifndef SYMVER +# define SYMVER(cn, vn) __asm__(".symver " #cn "," vn) +#endif + #ifdef HAVE_VISIBILITY_ATTRIBUTE # pragma GCC visibility push(default) #endif @@ -35,66 +56,78 @@ int libattr_setxattr(const char *path, const char *name, { return syscall(__NR_setxattr, path, name, value, size, flags); } +SYMVER(libattr_setxattr, "setxattr@ATTR_1.0"); int libattr_lsetxattr(const char *path, const char *name, void *value, size_t size, int flags) { return syscall(__NR_lsetxattr, path, name, value, size, flags); } +SYMVER(libattr_lsetxattr, "lsetxattr@ATTR_1.0"); int libattr_fsetxattr(int filedes, const char *name, void *value, size_t size, int flags) { return syscall(__NR_fsetxattr, filedes, name, value, size, flags); } +SYMVER(libattr_fsetxattr, "fsetxattr@ATTR_1.0"); ssize_t libattr_getxattr(const char *path, const char *name, void *value, size_t size) { return syscall(__NR_getxattr, path, name, value, size); } +SYMVER(libattr_getxattr, "getxattr@ATTR_1.0"); ssize_t libattr_lgetxattr(const char *path, const char *name, void *value, size_t size) { return syscall(__NR_lgetxattr, path, name, value, size); } +SYMVER(libattr_lgetxattr, "lgetxattr@ATTR_1.0"); ssize_t libattr_fgetxattr(int filedes, const char *name, void *value, size_t size) { return syscall(__NR_fgetxattr, filedes, name, value, size); } +SYMVER(libattr_fgetxattr, "fgetxattr@ATTR_1.0"); ssize_t libattr_listxattr(const char *path, char *list, size_t size) { return syscall(__NR_listxattr, path, list, size); } +SYMVER(libattr_listxattr, "listxattr@ATTR_1.0"); ssize_t libattr_llistxattr(const char *path, char *list, size_t size) { return syscall(__NR_llistxattr, path, list, size); } +SYMVER(libattr_llistxattr, "llistxattr@ATTR_1.0"); ssize_t libattr_flistxattr(int filedes, char *list, size_t size) { return syscall(__NR_flistxattr, filedes, list, size); } +SYMVER(libattr_flistxattr, "flistxattr@ATTR_1.0"); int libattr_removexattr(const char *path, const char *name) { return syscall(__NR_removexattr, path, name); } +SYMVER(libattr_removexattr, "removexattr@ATTR_1.0"); int libattr_lremovexattr(const char *path, const char *name) { return syscall(__NR_lremovexattr, path, name); } +SYMVER(libattr_lremovexattr, "lremovexattr@ATTR_1.0"); int libattr_fremovexattr(int filedes, const char *name) { return syscall(__NR_fremovexattr, filedes, name); } +SYMVER(libattr_fremovexattr, "fremovexattr@ATTR_1.0"); #ifdef HAVE_VISIBILITY_ATTRIBUTE # pragma GCC visibility pop -- 2.35.1 Bug: https://bugs.gentoo.org/644048 Bug: https://bugs.gentoo.org/700116