In meson.build we check that functions are available using:
meson.get_compiler('c').has_function('foo')
which checks the following:
- if __stub_foo or __stub___foo are defined, return false
- if foo is declared (a pointer to the function can be taken), return true
- otherwise check for __builtin_memfd_create
_stub is documented by glibc as
It defines a symbol '__stub_FUNCTION' for each function
in the C library which is a stub, meaning it will fail
every time called, usually setting errno to ENOSYS.
So if __stub is defined, we know we don't want to use the glibc version, but
this doesn't tell us if the name itself is defined or not. If it _is_ defined,
and we define our replacement as an inline static function, we get an error:
In file included from ../src/basic/missing.h:1358:0,
from ../src/basic/util.h:47,
from ../src/basic/calendarspec.h:29,
from ../src/basic/calendarspec.c:34:
../src/basic/missing_syscall.h:65:19: error: static declaration of 'memfd_create' follows non-static declaration
static inline int memfd_create(const char *name, unsigned int flags) {
^~~~~~~~~~~~
.../usr/include/bits/mman-shared.h:46:5: note: previous declaration of 'memfd_create' was here
int memfd_create (const char *__name, unsigned int __flags) __THROW;
^~~~~~~~~~~~
To avoid this problem, call our inline functions different than glibc,
and use a #define to map the official name to our replacement.
Fixes#8099.
v2:
- use "missing_" as the prefix instead of "_"
v3:
- rebase and update for statx()
Unfortunately "statx" is also present in "struct statx", so the define
causes issues. Work around this by using a typedef.
I checked that systemd compiles with current glibc
(glibc-devel-2.26-24.fc27.x86_64) if HAVE_MEMFD_CREATE, HAVE_GETTID,
HAVE_PIVOT_ROOT, HAVE_SETNS, HAVE_RENAMEAT2, HAVE_KCMP, HAVE_KEYCTL,
HAVE_COPY_FILE_RANGE, HAVE_BPF, HAVE_STATX are forced to 0.
Setting HAVE_NAME_TO_HANDLE_AT to 0 causes an issue, but it's not because of
the define, but because of struct file_handle.
The Linux kernel exposes the birth time now for files through statx()
hence make use of it where available. We keep the xattr logic in place
for this however, since only a subset of file systems on Linux currently
expose the birth time. NFS and tmpfs for example do not support it. OTOH
there are other file systems that do support the birth time but might
not support xattrs (smb…), hence make the best of the two, in particular
in order to deal with journal files copied between file system types and
to maintain compatibility with older file systems that are updated to
newer version of the file system.
This is a legacy of autotools, where one detection routine used a different
prefix then the others.
$ git grep -e HAVE_DECL_ -l|xargs sed -i s/HAVE_DECL_/HAVE_/g
The current raw_clone function takes two arguments, the cloning flags and
a pointer to the stack for the cloned child. The raw cloning without
passing a "thread main" function does not make sense if a new stack is
specified, as it returns in both the parent and the child, which will fail
in the child as the stack is virgin. All uses of raw_clone indeed pass NULL
for the stack pointer which indicates that both processes should share the
stack address (so you better don't pass CLONE_VM).
This commit refactors the code to not require the caller to pass the stack
address, as NULL is the only sensible option. It also adds the magic code
needed to make raw_clone work on sparc64, which does not return 0 in %o0
for the child, but indicates the child process by setting %o1 to non-zero.
This refactoring is not plain aesthetic, because non-NULL stack addresses
need to get mangled before being passed to the clone syscall (you have to
apply STACK_BIAS), whereas NULL must not be mangled. Implementing the
conditional mangling of the stack address would needlessly complicate the
code.
raw_clone is moved to a separete header, because the burden of including
the assert machinery and sched.h shouldn't be applied to every user of
missing_syscalls.h
We have a bunch of syscall wrapper definitions and it's easier to
see that they follow the same pattern if they are not interspersed
with other defines.
Change the wrappers to be uniform:
- if __NR_XXX is not defined, do not bother to call the syscall,
and return -1/ENOSYS immediately.
- do not check __NR_XXX defines if we detect the symbol as defined,
since we don't need them anyway
- reindent stuff for readability
New file basic/missing_syscall.h is included at the end of missing.h
because it might make use of some of the definitions in missing.h.
