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.
for some reason I have not been able to determine, gcc 3.2 rejects the
array notation. this seems to be a gcc bug, but since it's easy to
work around, let's do the workaround and avoid gratuitously requiring
newer compilers.
previously, shared library constructors were being called before
important internal things like the environment (extern char **environ)
and hwcap flags (needed for sjlj to work right with float on arm) were
initialized in __libc_start_main. rather than trying to have to
dynamic linker make sure this stuff all gets initialized right, I've
opted to just defer calling shared library constructors until after
the main program's entry point is reached. this also fixes the order
of ctors to be the exact reverse of dtors, which is a desirable
property and possibly even mandated by some languages.
the main practical effect of this change is that shared libraries
calling getenv from ctors will no longer fail.
it's essential to decrement the stack pointer before writing to new
stack space, rather than afterwards. otherwise there is a race
condition during which asynchronous code (signals) could clobber the
data being stored.
it may be possible to optimize the code further using stwu, but I
wanted to avoid making any changes to the actual stack layout in this
commit. further improvements can be made separately if desired.
based on proposal by Isaac Dunham. nonexistance of bits/io.h will
cause inclusion of sys/io.h to produce an error on archs that are not
supposed to have it. this is probably the desired behavior, but the
error message may be a bit unusual.
similar to exp.c cleanup: use scalbnf, don't return excess precision,
drop some optimizatoins.
exp.c was changed to be more consistent with expf.c code.
fortunately the memory corruption could not hurt anything, but it
prevented clearing the final newline and thus prevented the last path
element from working.
priority inheritance is not yet supported, and priority protection
probably will not be supported ever unless there's serious demand for
it (it's a fairly heavy-weight feature).
per-thread cpu clocks would be nice to have, but to my knowledge linux
is still not capable of supporting them. glibc fakes them by using the
_process_ cpu-time clock and subtracting the thread creation time,
which gives seriously incorrect semantics (worse than not supporting
the feature at all), so until there's a way to do it right, it will
remain as a stub that always fails.
overflow and underflow was incorrect when the result was not stored.
an optimization for the 0.5*ln2 < |x| < 1.5*ln2 domain was removed.
did various cleanups around static constants and made the comments
consistent with the code.
incomplete but at least partly working. requires all files to be
compiled in the new "secure" plt model, not the old one that put plt
code in the data segment. TLS is untested but may work. invoking the
dynamic linker explicitly to load a program does not yet handle argv
correctly.
the volatile hack in STRICT_ASSIGN is only needed if
assignment is not respected and excess precision is kept.
gcc -fexcess-precision=standard and -ffloat-store both
respect assignment and musl use these flags by default.
i kept the macro for now so the workaround may be used
for bad compilers in the future.
old code was correct only if the result was stored (without the
excess precision) or musl was compiled with -ffloat-store.
now we use STRICT_ASSIGN to work around the issue.
(see note 160 in c11 section 6.8.6.4)
old code was correct only if the result was stored (without the
excess precision) or musl was compiled with -ffloat-store.
(see note 160 in n1570.pdf section 6.8.6.4)
POSIX includes mostly-useless attribute-get functions for each
attribute-set function, presumably out of some object-oriented
dogmatism. the get functions are not useful with the simple idiomatic
usage of attributes. there are of course possible valid uses of them
(like writing wrappers for pthread init functions that perform special
actions on the presence of certain attributes), but considering how
tiny these functions are anyway, little is lost by putting them all in
one file, and some build-time cost and archive-file-size benefits are
achieved.
linux's sched_* syscalls actually implement the TPS (thread
scheduling) functionality, not the PS (process scheduling)
functionality which the sched_* functions are supposed to have.
omitting support for the PS option (and having the sched_* interfaces
fail with ENOSYS rather than omitting them, since some broken software
assumes they exist) seems to be the only conforming way to do this on
linux.
this function does not obey the normal calling convention; like a
syscall instruction, it's expected not to clobber any registers except
the return value. clobbering edx could break callers that were reusing
the value cached in edx after the syscall returns.
per interpretation for austin group issue #626, fflush(0) and exit()
must block waiting for a lock if another thread has locked a memory
stream with flockfile. this adds some otherwise-unnecessary
synchronization cost to use of memory streams, but there was already a
synchronization cost calling malloc anyway.
previously the stream was only added to the open file list in
single-threaded programs, so that upon subsequent call to
pthread_create, locking could be turned on for the stream.
Rich Felker