add synchronouse and asynchronous tag check failure codes, see
linux commit 74f1082487feb90bbf880af14beb8e29c3030c9f
arm64: mte: Add specific SIGSEGV codes
these are for the aarch64 MTE (memory tagging extension), see
linux commit 1c101da8b971a36695319dce7a24711dc567a0dd
arm64: mte: Allow user control of the tag check mode via prctl()
linux commit af5ce95282dc99d08a27a407a02c763dde1c5558
arm64: mte: Allow user control of the generated random tags via prctl()
path resolution does not follow symlinks on nosymfollow mounts (but
readlink still does), see
linux commit dab741e0e02bd3c4f5e2e97be74b39df2523fc6e
Add a "nosymfollow" mount option.
can cause rseq restart on another cpu to synchronize with global
memory access from rseq critical sections, see
linux commit 2a36ab717e8fe678d98f81c14a0b124712719840
rseq/membarrier: Add MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ
mainly added to linux to allow a central process management service in
android to give MADV_COLD|PAGEOUT hints for other processes, see
linux commit ecb8ac8b1f146915aa6b96449b66dd48984caacc
mm/madvise: introduce process_madvise() syscall: an external memory
hinting API
the threshold was wrong so expm1f overflowed to inf a bit too early
and on most targets uint32_t compare is faster than float compare so
use that.
this also fixes sinhf incorrectly returning nan for some values where
the internal expm1f overflowed.
on some negative inputs (e.g. -0x1.1e6ae8p+5) acoshf failed to return
nan. ensure that negative inputs result nan without introducing new
branches. this was tried before in
commit 101e601285
math: fix acoshf on negative values
but that fix was wrong. there are 3 formulas used:
log1p(x-1 + sqrt((x-1)*(x-1)+2*(x-1)))
log(2*x - 1/(x+sqrt(x*x-1)))
log(x) + 0.693147180559945309417232121458176568
the first fails on large negative inputs (may compute log1p(0) or
log1p(inf)), the second one fails on some mid range or large negative
inputs (may compute log(large) or log(inf)) and the last one fails on
-0 (returns -inf).
Update fanotify.h, see
linux commit 929943b38daf817f2e6d303ea04401651fc3bc05
fanotify: add support for FAN_REPORT_NAME
linux commit 83b7a59896dd24015a34b7f00027f0ff3747972f
fanotify: add basic support for FAN_REPORT_DIR_FID
linux commit 08b95c338e0c5a96e47f4ca314ea1e7580ecb5d7
fanotify: remove event FAN_DIR_MODIFY
FAN_DIR_MODIFY that was new in v5.7 is now removed from linux uapi,
but kept in musl, so we don't break api, linux cannot reuse the
value anyway.
see
linux commit 9b4feb630e8e9801603f3cab3a36369e3c1cf88d
arch: wire-up close_range()
linux commit 278a5fbaed89dacd04e9d052f4594ffd0e0585de
open: add close_range()
Ethernet protocol number for media redundancy protocol, see
linux commit 4714d13791f831d253852c8b5d657270becb8b2a
bridge: uapi: mrp: Add mrp attributes.
the linux faccessat syscall lacks a flag argument that is necessary
to implement the posix api, see
linux commit c8ffd8bcdd28296a198f237cc595148a8d4adfbe
vfs: add faccessat2 syscall
add TCP_NLA_BYTES_NOTSENT and new tcp_zerocopy_receive fields, see
linux commit c8856c051454909e5059df4e81c77b9c366c5515
tcp-zerocopy: Return inq along with tcp receive zerocopy.
linux commit 33946518d493cdf10aedb4a483f1aa41948a3dab
tcp-zerocopy: Return sk_err (if set) along with tcp receive zerocopy.
linux commit e08ab0b377a1489760533424437c5f4be7f484a4
tcp: add bytes not sent to SCM_TIMESTAMPING_OPT_STATS
it remaps anon mappings without unmapping the original. chromeos plans
to use it with userfaultfd, see:
linux commit e346b3813067d4b17383f975f197a9aa28a3b077
mm/mremap: add MREMAP_DONTUNMAP to mremap()
see
linux commit 9e2ba2c34f1922ca1e0c7d31b30ace5842c2e7d1
fanotify: send FAN_DIR_MODIFY event flavor with dir inode and name
linux commit 44d705b0370b1d581f46ff23e5d33e8b5ff8ec58
fanotify: report name info for FAN_DIR_MODIFY event
added in
linux commit 1a50ec0b3b2e9a83f1b1245ea37a853aac2f741c
arm64: Implement archrandom.h for ARMv8.5-RNG
linux commit d4209d8b717311d114b5d47ba7f8249fd44e97c2
arm64: cpufeature: Export matrix and other features to userspace
these were missed before, added in
linux commit 1201937491822b61641c1878ebcd16a93aed4540
arm64: Expose ARMv8.5 CondM capability to userspace
linux commit ca9503fc9e9812aa6258e55d44edb03eb30fc46f
arm64: Expose FRINT capabilities to userspace
reuses a bit from CSIGNAL so it can only be used with unshare
and clone3, added in
linux commit 769071ac9f20b6a447410c7eaa55d1a5233ef40c
ns: Introduce Time Namespace
needed for storage drivers with userspace component that may
run in the IO path, see
linux commit 8d19f1c8e1937baf74e1962aae9f90fa3aeab463
prctl: PR_{G,S}ET_IO_FLUSHER to support controlling memory reclaim
The use of TCP_ in udp.h is not known, fortunately udp.h is not
specified by posix so there are no strict namespace rules, added in
linux commit e27cca96cd68fa2c6814c90f9a1cfd36bb68c593
xfrm: add espintcp (RFC 8229)
TCP_NLA_TIMEOUT_REHASH queries timeout-triggered rehash attempts,
tcpm_ifindex limits the scope of TCP_MD5SIG* sockopt to a device.
see
linux commit 32efcc06d2a15fa87585614d12d6c2308cc2d3f3
tcp: export count for rehash attempts
linux commit 6b102db50cdde3ba2f78631ed21222edf3a5fb51
net: Add device index to tcp_md5sig
add IPPROTO_ETHERNET and IPPROTO_MPTCP, see
linux commit 2677625387056136e256c743e3285b4fe3da87bb
seg6: fix SRv6 L2 tunnels to use IANA-assigned protocol number
linux commit faf391c3826cd29feae02078ca2022d2f912f7cc
tcp: Define IPPROTO_MPTCP
also added clone3 on sh and m68k, on sh it's still missing (not
yet wired up), but reserved so safe to add.
see
linux commit fddb5d430ad9fa91b49b1d34d0202ffe2fa0e179
open: introduce openat2(2) syscall
linux commit 9a2cef09c801de54feecd912303ace5c27237f12
arch: wire up pidfd_getfd syscall
linux commit 8649c322f75c96e7ced2fec201e123b2b073bf09
pid: Implement pidfd_getfd syscall
linux commit e8bb2a2a1d51511e6b3f7e08125d52ec73c11139
m68k: Wire up clone3() syscall
longjmp should set the return value of setjmp, but 64bit
registers were used for the 0 check while the type is int.
use the code that gcc generates for return val ? val : 1;
same approach as in sqrt.
sqrtl was broken on aarch64, riscv64 and s390x targets because
of missing quad precision support and on m68k-sf because of
missing ld80 sqrtl.
this implementation is written for quad precision and then
edited to make it work for both m68k and x86 style ld80 formats
too, but it is not expected to be optimal for them.
note: using fp instructions for the initial estimate when such
instructions are available (e.g. double prec sqrt or rsqrt) is
avoided because of fenv correctness.
same method as in sqrt, this was tested on all inputs against
an sqrtf instruction. (the only difference found was that x86
sqrtf does not signal the x86 specific input-denormal exception
on negative subnormal inputs while the software sqrtf does,
this is fine as it was designed for ieee754 exceptions only.)
there is known faster method:
"Computing Floating-Point Square Roots via Bivariate Polynomial Evaluation"
that computes sqrtf directly via pipelined polynomial evaluation
which allows more parallelism, but the design does not generalize
easily to higher precisions.
approximate 1/sqrt(x) and sqrt(x) with goldschmidt iterations.
this is known to be a fast method for computing sqrt, but it is
tricky to get right, so added detailed comments.
use a lookup table for the initial estimate, this adds 256bytes
rodata but it can be shared between sqrt, sqrtf and sqrtl.
this saves one iteration compared to a linear estimate.
this is for soft float targets, but it supports fenv by using a
floating-point operation to get the final result. the result
is correctly rounded in all rounding modes. if fenv support is
turned off then the nearest rounded result is computed and
inexact exception is not signaled.
assumes fast 32bit integer arithmetics and 32 to 64bit mul.
The final rounding operation should be done with the correct sign
otherwise huge results may incorrectly get rounded to or away from
infinity in upward or downward rounding modes.
This affected sinh and sinhf which set the sign on the result after
a potentially overflowing mul. There may be other non-nearest rounding
issues, but this was a known long standing issue with large ulp error
(depending on how ulp is defined near infinity).
The fix should have no effect on sinh and sinhf performance but may
have a tiny effect on cosh and coshf.
Handle when after reduction |y| > pi/4+tiny. This happens in directed
rounding modes because the fast round to int code does not give the
nearest integer. In such cases the reduction may not be symmetric
between x and -x so e.g. cos(x)==cos(-x) may not hold (but polynomial
evaluation is not symmetric either with directed rounding so fixing
that would require more changes with bigger performance impact).
The fix only adds two predictable branches in nearest rounding mode,
simple ubenchmark does not show relevant performance regression in
nearest rounding mode.
The code could be improved: e.g reducing the medium size threshold
such that two step reduction is enough instead of three, and the
single precision case can avoid the issue by doing the round to int
differently, but this fix was kept minimal.
the syscall numbers were reserved in v5.3 but not wired up on mips, see
linux commit 0671c5b84e9e0a6d42d22da9b5d093787ac1c5f3
MIPS: Wire up clone3 syscall
mips application specific isa extensions were previously not exported
in hwcaps so userspace could not apply optimized code at runtime.
linux commit 38dffe1e4dde1d3174fdce09d67370412843ebb5
MIPS: elf_hwcap: Export userspace ASEs
allows waiting on a pidfd, in the future it might allow retrieving the
exit status by a non-parent process, see
linux commit 3695eae5fee0605f316fbaad0b9e3de791d7dfaf
pidfd: add P_PIDFD to waitid()
tcpi_rcv_ooopack for tracking connection quality:
linux commit f9af2dbbfe01def62765a58af7fbc488351893c3
tcp: Add TCP_INFO counter for packets received out-of-order
tcpi_snd_wnd peer window size for diagnosing tcp performance problems:
linux commit 8f7baad7f03543451af27f5380fc816b008aa1f2
tcp: Add snd_wnd to TCP_INFO
per thread prctl commands to relax the syscall abi such that top bits
of user pointers are ignored in the kernel. this allows the use of
those bits by hwasan or by mte to color pointers and memory on aarch64:
linux commit 63f0c60379650d82250f22e4cf4137ef3dc4f43d
arm64: Introduce prctl() options to control the tagged user addresses ABI
These were mainly introduced so android can optimize the memory usage
of unused apps.
MADV_COLD hints that the memory range is currently not needed (unlike
with MADV_FREE the content is not garbage, it needs to be swapped):
linux commit 9c276cc65a58faf98be8e56962745ec99ab87636
mm: introduce MADV_COLD
MADV_PAGEOUT hints that the memory range is not needed for a long time
so it can be reclaimed immediately independently of memory pressure
(unlike with MADV_DONTNEED the content is not garbage):
linux commit 1a4e58cce84ee88129d5d49c064bd2852b481357
mm: introduce MADV_PAGEOUT
the syscall number is reserved on all targets, but it is not wired up
on all targets, see
linux commit 8f6ccf6159aed1f04c6d179f61f6fb2691261e84
Merge tag 'clone3-v5.3' of ... brauner/linux
linux commit 8f3220a806545442f6f26195bc491520f5276e7c
arch: wire-up clone3() syscall
linux commit 7f192e3cd316ba58c88dfa26796cf77789dd9872
fork: add clone3
see
linux commit 7615d9e1780e26e0178c93c55b73309a5dc093d7
arch: wire-up pidfd_open()
linux commit 32fcb426ec001cb6d5a4a195091a8486ea77e2df
pid: add pidfd_open()
ptrace API to get details of the syscall the tracee is blocked in, see
linux commit 201766a20e30f982ccfe36bebfad9602c3ff574a
ptrace: add PTRACE_GET_SYSCALL_INFO request
the align attribute was used to keep the layout the same across targets
e.g. on m68k uint32_t is 2 byte aligned, this helps with compat ptrace.
Both sqrt and sqrtf shifted the signed exponent as signed int to adjust
the bit representation of the result. There are signed right shifts too
in the code but those are implementation defined and are expected to
compile to arithmetic shift on supported compilers and targets.
Several math functions are now from the ARM optimized-routines repo
licensed under standard MIT terms and copyrighted by Arm Limited,
so mention this in the COPYRIGHT too.
Some declarations of __tls_get_new were left in the code, even
though the definition got removed in
commit 9d44b6460a
install dynamic tls synchronously at dlopen, streamline access
this can make the build fail with
ld: lib/libc.so: hidden symbol `__tls_get_new' isn't defined
when libc.so is linked without --gc-sections, because a .hidden
declaration in asm code creates a reference even if the symbol
is not actually used.
lrint in (LONG_MAX, 1/DBL_EPSILON) and in (-1/DBL_EPSILON, LONG_MIN)
is not trivial: rounding to int may be inexact, but the conversion to
int may overflow and then the inexact flag must not be raised. (the
overflow threshold is rounding mode dependent).
this matters on 32bit targets (without single instruction lrint or
rint), so the common case (when there is no overflow) is optimized by
inlining the lrint logic, otherwise the old code is kept as a fallback.
on my laptop an i486 lrint call is asm:10ns, old c:30ns, new c:21ns
on a smaller arm core: old c:71ns, new c:34ns
on a bigger arm core: old c:27ns, new c:19ns
armv8 removed the coprocessor instructions other than cp14, so
on an armv8 system the related hwcaps should never be set.
new llvm complains about the use of coprocessor instructions in
armv8-a mode (even though they are never executed at runtime),
so ifdef them out when musl is built for armv8.
AT_HWCAP2 flags, see
linux commit 671db581815faf17cbedd7fcbc48823a247d90b1
arm64: Expose DC CVADP to userspace
linux commit 06a916feca2b262ab0c1a2aeb68882f4b1108a07
arm64: Expose SVE2 features for userspace
new mount api syscalls were added, same numers on all targets, see
linux commit a07b20004793d8926f78d63eb5980559f7813404
vfs: syscall: Add open_tree(2) to reference or clone a mount
linux commit 2db154b3ea8e14b04fee23e3fdfd5e9d17fbc6ae
vfs: syscall: Add move_mount(2) to move mounts around
linux commit 24dcb3d90a1f67fe08c68a004af37df059d74005
vfs: syscall: Add fsopen() to prepare for superblock creation
linux commit ecdab150fddb42fe6a739335257949220033b782
vfs: syscall: Add fsconfig() for configuring and managing a context
linux commit 93766fbd2696c2c4453dd8e1070977e9cd4e6b6d
vfs: syscall: Add fsmount() to create a mount for a superblock
linux commit cf3cba4a429be43e5527a3f78859b1bfd9ebc5fb
vfs: syscall: Add fspick() to select a superblock for reconfiguration
linux commit 9c8ad7a2ff0bfe58f019ec0abc1fb965114dde7d
uapi, x86: Fix the syscall numbering of the mount API syscalls [ver #2]
linux commit d8076bdb56af5e5918376cd1573a6b0007fc1a89
uapi: Wire up the mount API syscalls on non-x86 arches [ver #2]
apply open_tree with OPEN_TREE_CLONE call to the entire subtree, see
linux commit a07b20004793d8926f78d63eb5980559f7813404
vfs: syscall: Add open_tree(2) to reference or clone a mount
see
linux commit a528d35e8bfcc521d7cb70aaf03e1bd296c8493f
statx: Add a system call to make enhanced file info available
these are linux specific and not reserved names for fcntl.h so they
are under _BSD_SOURCE|_GNU_SOURCE.
ethertype for fake VLAN header for DSA, see
linux commit bf5bc3ce8a8f32a0d45b6820ede8f9fc3e9c23df
ether: Add dedicated Ethertype for pseudo-802.1Q DSA tagging
Using common code path for all symbol lookups fixes three dlsym issues:
- st_shndx of STT_TLS symbols were not checked and thus an undefined
tls symbol reference could be incorrectly treated as a definition
(the sysv hash lookup returns undefined symbols, gnu does not, so should
be rare in practice).
- symbol binding was not checked so a hidden symbol may be returned
(in principle STB_LOCAL symbols may appear in the dynamic symbol table
for hidden symbols, but linkers most likely don't produce it).
- mips specific behaviour was not applied (ARCH_SYM_REJECT_UND) so
undefined symbols may be returned on mips.
always_inline is used to avoid relocation performance regression, the
code generation for find_sym should not be affected.
syscall numbers are now synced up across targets (starting from 403 the
numbers are the same on all targets other than an arch specific offset)
IPC syscalls sem*, shm*, msg* got added where they were missing (except
for semop: only semtimedop got added), the new semctl, shmctl, msgctl
imply IPC_64, see
linux commit 0d6040d4681735dfc47565de288525de405a5c99
arch: add split IPC system calls where needed
new 64bit time_t syscall variants got added on 32bit targets, see
linux commit 48166e6ea47d23984f0b481ca199250e1ce0730a
y2038: add 64-bit time_t syscalls to all 32-bit architectures
new async io syscalls got added, see
linux commit 2b188cc1bb857a9d4701ae59aa7768b5124e262e
Add io_uring IO interface
linux commit edafccee56ff31678a091ddb7219aba9b28bc3cb
io_uring: add support for pre-mapped user IO buffers
a new syscall got added that uses the fd of /proc/<pid> as a stable
handle for processes: allows sending signals without pid reuse issues,
intended to eventually replace rt_sigqueueinfo, kill, tgkill and
rt_tgsigqueueinfo, see
linux commit 3eb39f47934f9d5a3027fe00d906a45fe3a15fad
signal: add pidfd_send_signal() syscall
on some targets (arm, m68k, s390x, sh) some previously missing syscall
numbers got added as well.
Linux v5.1 introduced ipc syscalls on targets where previously only
SYS_ipc was available, change the logic such that the ipc code keeps
using SYS_ipc which works backward compatibly on older kernels.
This changes behaviour on microblaze which had both mechanisms, now
SYS_ipc will be used instead of separate syscalls.
to request or change pointer auth keys for criu via ptrace, new in
linux commit d0a060be573bfbf8753a15dca35497db5e968bb0
arm64: add ptrace regsets for ptrauth key management
RFC 4286: "The IPv4 multicast address for All-Snoopers is 224.0.0.106."
from
linux commit 4effd28c1245303dce7fd290c501ac2c11052114
bridge: join all-snoopers multicast address
SO_BINDTOIFINDEX behaves similar to SO_BINDTODEVICE, but takes a
network interface index as argument, rather than the network
interface name. see
linux commit f5dd3d0c9638a9d9a02b5964c4ad636f06cf7e2c
net: introduce SO_BINDTOIFINDEX sockopt
restricts router alert packets received by the socket to the
socket's namespace only. see
linux commit 9036b2fe092a107856edd1a3bad48b83f2b45000
net: ipv6: add socket option IPV6_ROUTER_ALERT_ISOLATE
allows specifying that the speculative store bypass disable bit should
be cleared on exec. see
linux commit 71368af9027f18fe5d1c6f372cfdff7e4bde8b48
x86/speculation: Add PR_SPEC_DISABLE_NOEXEC
needed for android so it can migrate from its ashmem to memfd.
allows making the memfd readonly for future users while keeping
a writable mmap of it. see
linux commit ab3948f58ff841e51feb845720624665ef5b7ef3
mm/memfd: add an F_SEAL_FUTURE_WRITE seal to memfd
includes changes from linux v5.1
linux commit 235328d1fa4251c6dcb32351219bb553a58838d2
fanotify: add support for create/attrib/move/delete events
linux commit 5e469c830fdb5a1ebaa69b375b87f583326fd296
fanotify: copy event fid info to user
linux commit e9e0c8903009477b630e37a8b6364b26a00720da
fanotify: encode file identifier for FAN_REPORT_FID
as well as earlier changes that were missed.
sys/statfs.h is included for fsid_t.
currently the bfd linker does not seem to create tls segments where
p_vaddr%p_align != 0, but this is valid in ELF and then the runtime
computed tls offset must satisfy
offset%p_align == (base+p_vaddr)%p_align
and in case of local exec tls (main executable) the smallest such
offset must be used (otherwise it is incompatible with the offset
computed by the static linker). the !TLS_ABOVE_TP case is handled
correctly (the offset is negative then in the formula).
the ldso code for TLS_ABOVE_TP is changed so the static tls offset
of each module satisfies the formula.
tls_offset should always point to the end of the allocated static tls
area, but this was not handled correctly on "tls variant 1" targets
in the dynamic linker:
after application tls was allocated, tls_offset was aligned up,
potentially wasting tls space. (alignment may be needed at the
begining of the tls area, not at the end, but that will be fixed
separately as it is unlikely to affect real binaries.)
when static tls was allocated for a shared library, tls_offset was
only updated with the size of the tls segment which does not include
alignment gaps, which can easily happen if the tls size update for
one library leaves tls_offset misaligned for the next one. this can
cause oob access in __copy_tls or arbitrary breakage at tls access.
(the issue was observed on aarch64 with rust binaries)
from https://github.com/ARM-software/optimized-routines,
commit 04884bd04eac4b251da4026900010ea7d8850edc
The underflow exception is signaled if the result is in the subnormal
range even if the result is exact.
code size change: +3421 bytes.
benchmark on x86_64 before, after, speedup:
-Os:
pow rthruput: 102.96 ns/call 33.38 ns/call 3.08x
pow latency: 144.37 ns/call 54.75 ns/call 2.64x
-O3:
pow rthruput: 98.91 ns/call 32.79 ns/call 3.02x
pow latency: 138.74 ns/call 53.78 ns/call 2.58x
from https://github.com/ARM-software/optimized-routines,
commit 04884bd04eac4b251da4026900010ea7d8850edc
POWF_SCALE != 1.0 case only matters if TOINT_INTRINSICS is set, which
is currently not supported for any target.
SNaN is not supported, it would require an issignalingf
implementation.
code size change: -816 bytes.
benchmark on x86_64 before, after, speedup:
-Os:
powf rthruput: 95.14 ns/call 20.04 ns/call 4.75x
powf latency: 137.00 ns/call 34.98 ns/call 3.92x
-O3:
powf rthruput: 92.48 ns/call 13.67 ns/call 6.77x
powf latency: 131.11 ns/call 35.15 ns/call 3.73x
Musl currently aims to support non-nearest rounding mode and does not
support SNaNs. These macros allow marking relevant code paths in case
these decisions are changed later (they also help documenting the
corner cases involved).
These don't have an effectw with -Os so not useful with default settings
other than documenting the expectation.
With --enable-optimize=internal,malloc,string,math the libc.so code size
increases by 18K on x86_64 and performance varies in -2% .. +10%.
These are supposed to be used in tail call positions when handling
special cases in new code. (fp exceptions may be raised "naturally"
by the common code path if special casing is more effort.)
This implements the error handling apis used in
https://github.com/ARM-software/optimized-routines
without errno setting.
Previously type casts or assignments were used for handling excess
precision, which assumed standard C99 semantics, but since it's a
rarely needed obscure detail, it's better to use explicit helper
functions to document where we rely on this. It also helps if the
code is used outside of the libc in non-C99 compilation mode: with the
default excess precision handling of gcc, explicit inline asm barriers
are needed for narrowing on FLT_EVAL_METHOD!=0 targets.
I plan to use this in new code with the existing style that uses
double_t and float_t as much as possible.
One ugliness is that it is required for almost every return statement
since that does not drop excess precision (the standard changed this
in C11 annex F, but that does not help in non-standard compilation
modes or with old compilers).
C99 has ways to support fenv access, but compilers don't implement it
and assume nearest rounding mode and no fp status flag access. (gcc has
-frounding-math and then it does not assume nearest rounding mode, but
it still assumes the compiled code itself does not change the mode.
Even if the C99 mechanism was implemented it is not ideal: it requires
all code in the library to be compiled with FENV_ACCESS "on" to make it
usable in non-nearest rounding mode, but that limits optimizations more
than necessary.)
The math functions should give reasonable results in all rounding modes
(but the quality may be degraded in non-nearest rounding modes) and the
fp status flag settings should follow the spec, so fenv side-effects are
important and code transformations that break them should be prevented.
Unfortunately compilers don't give any help with this, the best we can
do is to add fp barriers to the code using volatile local variables
(they create a stack frame and undesirable memory accesses to it) or
inline asm (gcc specific, requires target specific fp reg constraints,
often creates unnecessary reg moves and multiple barriers are needed to
express that an operation has side-effects) or extern call (only useful
in tail-call position to avoid stack-frame creation and does not work
with lto).
We assume that in a math function if an operation depends on the input
and the output depends on it, then the operation will be evaluated at
runtime when the function is called, producing all the expected fenv
side-effects (this is not true in case of lto and in case the operation
is evaluated with excess precision that is not rounded away). So fp
barriers are needed (1) to prevent the move of an operation within a
function (in case it may be moved from an unevaluated code path into an
evaluated one or if it may be moved across a fenv access), (2) force the
evaluation of an operation for its side-effect when it has no input
dependency (may be constant folded) or (3) when its output is unused. I
belive that fp_barrier and fp_force_eval can take care of these and they
should not be needed in hot code paths.
Nothing is left from the original fdlibm header nor from the bsd
modifications to it other than some internal api declarations.
Comments are dropped that may be copyrightable content.
This makes it easier to build musl math code with a compiler that
does not support complex types (tcc) and in general more sensible
factorization of the internal headers.
FP_FAST_FMA can be defined if "the fma function generally executes about
as fast as, or faster than, a multiply and an add of double operands",
which can only be true if the fma call is inlined as an instruction.
gcc sets __FP_FAST_FMA if __builtin_fma is inlined as an instruction,
but that does not mean an fma call will be inlined (e.g. it is defined
with -fno-builtin-fma), other compilers (clang) don't even have such
macro, but this is the closest we can get.
(even if the libc fma implementation is a single instruction, the extern
call overhead is already too big when the macro is used to decide between
x*y+z and fma(x,y,z) so it cannot be based on libc only, defining the
macro unconditionally on targets which have fma in the base isa is also
incorrect: the compiler might not inline fma anyway.)
this solution works with gcc unless fma inlining is explicitly turned off.
HWCAP_SB - speculation barrier instruction available added in linux
commit bd4fb6d270bc423a9a4098108784f7f9254c4e6d
HWCAP_PACA, HWCAP_PACG - pointer authentication instructions available
(address and generic) added in linux commit
7503197562567b57ec14feb3a9d5400ebc56812f
aarch64 pointer authentication code related prctl that allows
reinitializing the key for the thread, added in linux commit
ba830885656414101b2f8ca88786524d4bb5e8c1
NT_MIPS_MSA for ptrace access to mips simd arch reg set, added in linux
commit 3cd640832894b85b5929d5bda74505452c800421
NT_ARM_PAC_MASK for ptrace access to pointer auth code mask, added in
commit ec6e822d1a22d0eef1d1fa260dff751dba9a4258
C-SKY support was added to binutils 2.32 in commit
b8891f8d622a31306062065813fc278d8a94fe21
the elf.h change was added to glibc 2.29 in commit
4975f0c3d0131fdf697be0b1631c265e5fd39088
