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This ensures that the musl definition of 'struct iphdr' does not conflict
with the Linux kernel UAPI definition of it.

Some software, i.e. net-tools, will not compile against 5.4 kernel headers
without this patch and the corresponding Linux kernel patch.

renameat(2) is supposed to ignore if old or new is a hardlink to the other.
However, the way this is written, it also ignores if old or new are symlinks
to one another.  This is incorrect.

- Fail if old or new is longer than PATH_MAX with ENAMETOOLONG.

- Fail if old or new is 0 bytes long.

- Fail if old or new has dot or dot-dot as the last component of their
  path name.

The Linux kernel provides none of these behaviours.

These interfaces are all scheduled for addition in Issue 8.

They cannot be available if _XOPEN_SOURCE is <= 700, or
_POSIX_C_SOURCE is <= 200809L.

Quentin Rameau authored Mar 11, 2018 and A. Wilcox committed Dec 08, 2019

As Rick stated, this isn't a clean solution because argv can be
arbirtary long and overflow the stack.

I post it here in case you'd find it useful anyway.

The timespec_get function, and TIME_* macros, are only in C11.

Since musl is compiled with -std=c99, TIME_UTC is unavailable in the
timespec_get implementation, so we use the raw value 1.

aligned_alloc, at_quick_exit, and quick_exit are new in C11 and C++11.
Only make these symbols visible in those versions, to avoid polluting
the namespace of C99 and POSIX 2008 sources.

This is not a POSIX function, it should not be visible there.

Right now, this is a worst-case assumption; some kernels may actually
have a value of 100000 here (100 Hz timers).  This is considered the
easiest implementation.

This is required to be present in <unistd.h>.

This is used to determine what CFLAGS/LDFLAGS are needed to enable
compilation with threads on musl.  We don't have any special ones, so
just return an empty string.

This is required to be present in <unistd.h>.

We definitely don't /support/ UUCP, so return -1 for it.
But this value is required to be present in <unistd.h>.

commit 4d3a162d overlooked that the
mips64 reloc.h dependent on endian.h not only for setting the ABI ldso
name to match the byte order, but also for use of the byte swapping
macros. they are needed to override R_TYPE, R_SYM, and R_INFO, to
compensate for a mips "quirk" of always using big endian order for
symbol references in relocations.

part of that commit canot be reverted because the original code was
wrong: it's invalid to define _GNU_SOURCE or any feature test macro
in reloc.h, or anywhere except at the top of a source file. however,
thanks to commit 316730cd, the feature
test macro is no longer needed to access the endian-swapping macros,
so simply bringing back the #include directive suffices.

commit de90f38e omitted $(srcdir) from
the makefile include pathname it added. since the include directive
was prefixed with - to make it optional (for archs that don't use it),
the failure to find arch/$(ARCH)/arch.mak was silent.

in commit 22daaea3, the
__dlsym_redir_time64 function providing the backend for __dlsym_time64
was defined only in the dynamic linker, and thus was undefined when
static linking a program referencing dlsym. use the same stub_dlsym
definition that provides __dlsym (the non-redirecting backend) for
static linked programs to provide it, conditional on _REDIR_TIME64.

now that all 32-bit archs have 64-bit time_t (and suseconds_t), the
arch-provided _Int64 macro (long or long long, as appropriate) can be
used to define them, and arch-specific definitions are no longer
needed.

now that all 32-bit archs have 64-bit time types, the values for the
time-related ioctls can be shared. the mechanism for this is an
arch/generic version of the bits header. archs which don't use the
generic header still need to duplicate the definitions.

x32, which does not use the new time64 values of the macros, already
has its own overrides, so this commit does not affect it.

now that all 32-bit archs have 64-bit time types, the values for the
time-related socket option macros can be treated as universal for
32-bit archs. the sys/socket.h mechanism for this predates
arch/generic and is instead in the top-level header.

x32, which does not use the new time64 values of the macros, already
has its own overrides, so this commit does not affect it.

this commit preserves ABI fully for existing interface boundaries
between libc and libc consumers (applications or libraries), by
retaining existing symbol names for the legacy 32-bit interfaces and
redirecting sources compiled against the new headers to alternate
symbol names. this does not necessarily, however, preserve the
pairwise ABI of libc consumers with one another; where they use
time_t-derived types in their interfaces with one another, it may be
necessary to synchronize updates with each other.

the intent is that ABI resulting from this commit already be stable
and permanent, but it will not be officially so until a release is
made. changes to some header-defined types that do not play any role
in the ABI between libc and its consumers may still be subject to
change.

mechanically, the changes made by this commit for each 32-bit arch are
as follows:

- _REDIR_TIME64 is defined to activate the symbol redirections in
  public headers

- COMPAT_SRC_DIRS is defined in arch.mak to activate build of ABI
  compat shims to serve as definitions for the original symbol names

- time_t and suseconds_t definitions are changed to long long (64-bit)

- IPC_STAT definition is changed to add the IPC_TIME64 bit (0x100),
  triggering conversion of semid_ds, shmid_ds, and msqid_ds split
  low/high time bits into new time_t members

- structs semid_ds, shmid_ds, msqid_ds, and stat are modified to add
  new 64-bit time_t/timespec members at the end, maintaining existing
  layout of other members.

- socket options (SO_*) and ioctl (sockios) command macros are
  redefined to use the kernel's "_NEW" values.

in addition, on archs where vdso clock_gettime is used, the
VDSO_CGT_SYM macro definition in syscall_arch.h is changed to use a
new time64 vdso function if available, and a new VDSO_CGT32_SYM macro
is added for use as fallback on kernels lacking time64.

these definitions are copied from generic bits/ioctl.h, so that x32
keeps the "_OLD" versions (which are already time64 on x32) when
32-bit archs switch to 64-bit time_t.

these definitions are merely copied from the top-level sys/socket.h,
so there is no functional change at this time. however, the top-level
definitions will change to use the time64 "_NEW" versions on 32-bit
archs when time_t is switched over to 64-bit. this commit ensures that
change will be suppressed on x32.

these structures can now be defined generically in terms of endianness
and long size. previously, the 32-bit archs all shared a common
definition from the generic bits header, and each 64-bit arch had to
repeat the 64-bit version, with endian conditionals if the arch had
variants of each endianness.

I would prefer getting rid of the preprocessor conditionals for
padding and instead using unnamed bitfield members, like commit
9b2921be did for struct timespec.
however, at present sendmsg, recvmsg, and recvmmsg need access to the
padding members by name to zero them. this could perhaps be cleaned up
in the future.

being that it contains pointers and (from the kernel perspective,
which is wrong) size_t members, x32 uses the 32-bit version of the
structure, not a half-32-bit, half-64-bit layout like we had here. the
x86_64 definition was inadvertently copied when x32 was first added.

unlike errors in the opposite direction (missing padding), this error
was not easily detected breakage, because the layout of the commonly
used initial subset of members still matched. breakage could only be
observed in the presence of control messages or flags.

SO_RCVTIMEO and SO_SNDTIMEO already were, but only in aggregate with
SO_DEBUG and all of the other low/traditional options that varied per
arch. SO_TIMESTAMP* are newly overridable. the two groups have to be
done separately since mips64 and powerpc64 will override the former
but not the latter.

at some point this should be cleaned up to use bits headers more
idiomatically.

the immediate usage case for this is to let 32-bit archs moving to
64-bit time_t via symbol redirection pull in wrapper shims that
provide the old symbol names. in the future it may be used for other
types of compatibility-only source files that are not relevant to all
archs.

if symbols are being redirected to provide the new time64 ABI, dlsym
must perform matching redirections; otherwise, it would poke a hole in
the magic and return pointers to functions that are not safe to call
from a caller using time64 types.

rather than duplicating a table of redirections, use the time64
symbols present in libc's symbol table to derive the decision for
whether a particular symbol needs to be redirected.

these files provide the symbols for the traditional 32-bit time_t ABI
on existing 32-bit archs by wrapping the real, internal versions of
the corresponding functions, which always work with 64-bit time_t.
they are written to be as agnostic as possible to the implementation
details of the real functions, so that they can be written once and
mostly forgotten, but they are aware of details of the old (and
sometimes new) ABI, which is okay since ABI is fixed and cannot
change.

a new compat tree is added, separate from src, which the Makefile does
not see or use now, but which archs will be able to add to the build
process. we could also consider moving other things that are compat
shims here, like functions which are purely for glibc-ABI-compat, with
the goal of making it optional or just cleaning up the main src tree
to make the distinction between actual implementation/API files and
ABI-compat shims clear.

here _REDIR_TIME64 is used as an indication that there's an old ABI,
and thereby the old time32 timespec fields of struct stat.

keeping struct stat compatible and providing both versions of the
timespec fields is done so that ftw/nftw does not need painful compat
shims, and (more importantly) so that similar interfaces between pairs
of libc consumers (applications/libraries) will be less likely to
break when one has been rebuilt for time64 but the other has not.

these functions cannot provide the glibc lfs64-ABI-compatible symbols
when time_t differs from what it was in that ABI. instead, the aliases
need to be provided by the time32 compat shims or through some other
mechanism.