to produce sorted results roughly corresponding to RFC 3484/6724,
__lookup_name computes routability and choice of source address via
dummy UDP connect operations (which do not produce any packets). since
at the logical level, the properties fed into the sort key are
computed on ipv6 addresses, the code was written to use the v4mapped
ipv6 form of ipv4 addresses and share a common code path for them all.
however, on kernels where ipv6 support has been completely omitted,
this causes ipv4 to appear equally unroutable as ipv6, thereby putting
unreachable ipv6 addresses before ipv4 addresses in the results.

instead, use only ipv4 sockets to compute routability for ipv4
addresses. some gratuitous conversion back and forth is left so that
the logic is not affected by these changes. it may be possible to
simplify the ipv4 case considerably, thereby reducing code size and
complexity.

Avoid saving/restoring the incoming argument by reusing memset return
value.

since slack space at the beginning and/or end of writable load maps is
donated to malloc, the application could obtain valid pointers in
these ranges which dladdr would erroneously identify as part of the
shared object whose mapping they came from.

instead of checking the queried address against the mapping base and
length, check it against the load segments from the program headers,
and only match the dso if it lies within the bounds of one of them.

as a shortcut, if the address does match the range of the mapping but
not any of the load segments, we know it cannot match any other dso
and can immediately return failure.

the early-exit condition for the symbol match loop on exact matches
caused dladdr to produce the first match for an exact match, but the
last match for an inexact match. in the interest of consistency,
require a strictly-closer match to replace an already-found one.

commit 8b8fb7f0 added logic to prevent
matching a symbol with no recorded size (closest-match) when there is
an intervening symbol whose size was recorded, but it only worked when
the intervening symbol was encountered later in the search.

instead of rejecting symbols where addr falls outside their recorded
size during the closest-match search, accept them to find the true
closest-match, then reject such a result only once the search has
finished.

based on patch by Axel Siebenborn, with fixes discussed on the mailing
list after submission and and rebased around the UB fix in commit
e829695f.

avoid spurious symbol matches by dladdr beyond symbol size. for
symbols with a size recorded, only match if the queried address lies
within the address range determined by the symbol address and size.
for symbols with no size recorded, the old closest-match behavior is
kept, as long as there is no intervening symbol with a recorded size.

the case where no symbol is matched, but the address does lie within
the memory range of a shared object, is specified as success. fix the
return value and produce a valid (with null dli_sname and dli_saddr)
Dl_info structure.

maintainer's note: past sentiment was that, despite being imperfect
and unable to force clearing of all possible copies of sensitive data
(e.g. in registers, register spills, signal contexts left on the
stack, etc.) this function would be added if major implementations
agreed on it, which has happened -- several BSDs and glibc all include
it.

maintainer's note: this change is for conformance with RFC 5952,
4.2.2, which explicitly forbids use of :: to shorten a single 16-bit 0
field when producing the canonical text representation for an IPv6
address. fixes a test failure reported by Philip Homburg, who also
submitted a patch, but this fix is simpler and should produce smaller
code.

the expression (tm->__tm_gmtoff)/3600 has type long. use %+.2ld instead.

if a final dot was included in the queried host name to anchor it to
the dns root/suppress search domains, and the result was not a CNAME,
the returned canonical name included the final dot. this was not
consistent with other implementations, confused some applications, and
does not seem desirable.

POSIX specifies returning a pointer to, or to a copy of, the input
nodename, when the canonical name is not available, but does not
attempt to specify what constitutes "not available". in the case of
search, we already have an implementation-defined "availability" of a
canonical name as the fully-qualified name resulting from search, so
defining it similarly in the no-search case seems reasonable in
addition to being consistent with other implementations.

as a bonus, fix the case where more than one trailing dot is included,
since otherwise the changes made here would wrongly cause lookups with
two trailing dots to succeed. previously this case resulted in
malformed dns queries and produced EAI_AGAIN after a timeout. now it
fails immediately with EAI_NONAME.

commit 587f5a53 moved the definition
of SO_PEERSEC to bits/socket.h for archs where the SO_* macros differ
from their standard values, but failed to add copies of the generic
definition for powerpc and powerpc64.

adapted from patch by Matthias Schiffer.

writable load segments can have size-in-memory larger than their size
in the ELF file, representing bss or equivalent. the initial partial
page has to be zero-filled, and additional anonymous pages have to be
mapped such that accesses don't failt with SIGBUS.

map_library skips redundant MAP_FIXED mapping of the initial
(lowest-address) segment when processing LOAD segments since it was
already mapped when reserving the virtual address range, but in doing
so, inadvertently also skipped the code to fill/map bss. typical
executable and library files have two or more LOAD segments, and the
first one is text/rodata (non-writable) and thus has no bss, but it is
syntactically valid for an ELF program/library to put its writable
segment first, or to have only one segment (everything writable). the
binutils bfd-based linker has been observed to create such programs in
the presence of unusual sections or linker scripts.

fix by moving only the mmap_fixed operation under the conditional
rather than skipping the remainder of the loop body. add a check to
avoid bss processing in the case where the segment is not writable;
this should not happen, but if it does, the change would be a crashing
regression without this check.

memfd_create was added in linux v3.17 and glibc has api for it.

mlock2 syscall was added in linux v4.4 and glibc has api for it.
It falls back to mlock in case of flags==0, so that case works
even on older kernels.

MLOCK_ONFAULT is moved under _GNU_SOURCE following glibc.

unlike the x86 variant, the m68k ld80 format allows (biased) exponent
zero with mantissa msb set, thereby extending the normal range.

the mode member of struct ipc_perm is specified by POSIX to have type
mode_t, which is uniformly defined as unsigned int. however, Linux
defines it with type __kernel_mode_t, and defines __kernel_mode_t as
unsigned short on some archs. since there is a subsequent padding
field, treating it as a 32-bit unsigned int works on little endian
archs, but the order is backwards on big endian archs with the
erroneous definition.

since multiple archs are affected, remedy the situation with fixup
code in the affected functions (shmctl, semctl, and msgctl) rather
than repeating the same shims in syscall_arch.h for every affected
arch.

new in linux commit 71406883fd35794d573b3085433c41d0a3bf6c21

new in linux commit 256211f2b0b251e532d1899b115e374feb16fa7a

hwcaps for armv8.4, new in linux commit
7206dc93a58fb76421c4411eefa3c003337bcb2d

PR_{SET,GET}_SPECULATION_CTRL controls speculation related vulnerability
mitigations, new in commits
b617cfc858161140d69cc0b5cc211996b557a1c7
356e4bfff2c5489e016fdb925adbf12a1e3950ee

added in linux commit 4fe0de5b143762d327bfaf1d7be7c5b58041a18c

new and missing netlink attributes types for SCM_TIMESTAMPING_OPT_STATS,
new ones were added in commits
7156d194a0772f733865267e7207e0b08f81b02b
be631892948060f44b1ceee3132be1266932071e
87ecc95d81d951b0984f2eb9c5c118cb68d0dce8

introduced to stat ipc objects without permission checks since the
info is available in /proc/sysvipc anyway, new in linux commits
23c8cec8cf679b10997a512abb1e86f0cedc42ba
a280d6dc77eb6002f269d58cd47c7c7e69b617b6
c21a6970ae727839a2f300cd8dd957de0d0238c3

to map at a fixed address without unmapping underlying mappings
(fails with EEXIST unlike MAP_FIXED), new in linux commits
4ed28639519c7bad5f518e70b3284c6e0763e650 and
a4ff8e8620d3f4f50ac4b41e8067b7d395056843.

add pkey_mprotect, pkey_alloc, pkey_free syscall numbers,
new in linux commits 3350eb2ea127978319ced883523d828046af4045
and 9499ec1b5e82321829e1c1510bcc37edc20b6f38

armv8.4 fp mul instructions.
added in commit 3b3b681097fae73b7f5dcdd42db6cfdf32943d4c

to get seccomp state for checkpoint restore.
added in linux commit 26500475ac1b499d8636ff281311d633909f5d20

struct tag follows the glibc api and ptrace_peeksiginfo_args
got changed too accordingly.

octets in ethernet type field
added in linux commit 4bbb3e0e8239f9079bf1fe20b3c0cb598714ae61

protocol number for erspan v2 support
added in linux commit f551c91de262ba36b20c3ac19538afb4f4507441

added to uapi in commit 65aaf87b3aa2d049c6b9fd85221858a895df3393
used since commit a9a08845e9acbd224e4ee466f5c1275ed50054e8,
which renamed POLL* to EPOLL* in the kernel.

three ABIs are supported: the default with 68881 80-bit fpu format and
results returned in floating point registers, softfloat-only with the
same format, and coldfire fpu with IEEE single/double only. only the
first is tested at all, and only under qemu which has fpu emulation
bugs.

basic functionality smoke tests have been performed for the most
common arch-specific breakage via libc-test and qemu user-level
emulation. some sysvipc failures remain, but are shared with other big
endian archs and will be fixed separately.

since x86 and m68k are the only archs with 80-bit long double and each
has mandatory endianness, select the variant via endianness.
differences are minor: apparently just byte order and representation
of infinities. the m68k format is not well-documented anywhere I could
find, so if other differences are found they may require additional
changes later.

In TLS variant I the TLS is above TP (or above a fixed offset from TP)
but on some targets there is a reserved gap above TP before TLS starts.

This matters for the local-exec tls access model when the offsets of
TLS variables from the TP are hard coded by the linker into the
executable, so the libc must compute these offsets the same way as the
linker.  The tls offset of the main module has to be

	alignup(GAP_ABOVE_TP, main_tls_align).

If there is no TLS in the main module then the gap can be ignored
since musl does not use it and the tls access models of shared
libraries are not affected.

The previous setup only worked if (tls_align & -GAP_ABOVE_TP) == 0
(i.e. TLS did not require large alignment) because the gap was
treated as a fixed offset from TP.  Now the TP points at the end
of the pthread struct (which is aligned) and there is a gap above
it (which may also need alignment).

The fix required changing TP_ADJ and __pthread_self on affected
targets (aarch64, arm and sh) and in the tlsdesc asm the offset to
access the dtv changed too.

since this iconv implementation's output is stateless, it's necessary
to know before writing anything to the output buffer whether the
conversion of the current input character will fit.

previously we used a hard-coded table of the output size needed for
each supported output encoding, but failed to update the table when
adding support for conversion to jis-based encodings and again when
adding separate encoding identifiers for implicit-endianness utf-16/32
and ucs-2/4 variants, resulting in out-of-bound table reads and
incorrect size checks. no buffer overflow was possible, but the
affected characters could be converted incorrectly, and iconv could
potentially produce an incorrect return value as a result.

remove the hard-coded table, and instead perform the recursive iconv
conversion to a temporary buffer, measuring the output size and
transferring it to the actual output buffer only if the whole
converted result fits.