the issue is identical to the recent commit fixing the mips versions:
despite other implementations doing this, it conflicts with the
requirements of ISO C and it's a waste of time and code size.
nothing in the standard requires or even allows the fenv state to be
restored by longjmp. restoring the exception flags is not such a big
deal since it's probably valid to clobber them completely, but
restoring the rounding mode yields an observable side effect not
sanctioned by ISO C. saving/restoring it also wastes a few cycles and
16 bytes of code.
as for historical behavior, reportedly SGI IRIX did save/restore fenv,
and this is where glibc and uClibc got the behavior from. a few other
systems save/restore it too (on archs other than mips), even though
this is apparently wrong. further details are documented here:
http://www-personal.umich.edu/~williams/archive/computation/setjmp-fpmode.html
as musl aims for standards conformance rather than coddling historical
programs expecting non-conforming behavior, and as it's unlikely that
any historical programs actually depend on the incorrect behavior
(such programs would break on other archs, anyway), I'm making the
change not to save/restore fenv on mips.
based on initial work by rdp, with heavy modifications. some features
including threads are untested because qemu app-level emulation seems
to be broken and I do not have a proper system image for testing.
not heavily tested, but at least they don't seem to break anything on
soft float targets with or without coprocessors. they check the auxv
AT_HWCAP flags to determine which coprocessor, if any, is available.
also fix the alignment of jmp_buf to meet the abi. linux always
emulates fpu on mips if it's not present, so enabling this code
unconditionally is "safe" but may be slow. in the long term it may be
preferable to find a way to disable it on soft float builds.
basically, this version of the code was obtained by starting with
rdp's work from his ellcc source tree, adapting it to musl's build
system and coding style, auditing the bits headers for discrepencies
with kernel definitions or glibc/LSB ABI or large file issues, fixing
up incompatibility with the old binutils from aboriginal linux, and
adding some new special cases to deal with the oddities of sigaction
and pipe syscall interfaces on mips.
at present, minimal test programs work, but some interfaces are broken
or missing. threaded programs probably will not link.
these changes are based on the following communication via email:
"I hereby grant that all of the code I have contributed to musl on or
before April 23, 2012 may be licensed under the terms of the following
MIT license:
Copyright (c) 2011-2012 Nicholas J. Kain
Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE."
this port assumes eabi calling conventions, eabi linux syscall
convention, and presence of the kernel helpers at 0xffff0f?0 needed
for threads support. otherwise it makes very few assumptions, and the
code should work even on armv4 without thumb support, as well as on
systems with thumb interworking. the bits headers declare this a
little endian system, but as far as i can tell the code should work
equally well on big endian.
some small details are probably broken; so far, testing has been
limited to qemu/aboriginal linux.
this seems to be necessary to make the linker accept the functions in
a shared library (perhaps to generate PLT entries?)
strictly speaking libc-internal asm should not need it. i might clean
that up later.
Rich Felker
rofl0r
Richard Pennington
Nicholas J. Kain