a while back, gcc switched from using the old _init/_fini fragments
method for calling ctors and dtors on arm to the __init_array and
__fini_array method. unfortunately, on glibc this depends on ugly
hacks involving making libc.so a linker script and pulling parts of
libc into the main program binary. so I cheat a little bit, and just
write asm to iterate over the init/fini arrays from the _init/_fini
asm. the same approach could be used on any arch it's needed on, but
for now arm is the only one.
this change fixes an obscure issue with some nonstandard kernels,
where the initial brk syscall returns a pointer just past the end of
bss rather than the beginning of a new page. in that case, the dynamic
linker has already reclaimed the space between the end of bss and the
page end for use by malloc, and memory corruption (allocating the same
memory twice) will occur when malloc again claims it on the first call
to brk.
if there's evidence of any use for it, we can add it back later. as
far as I can tell, glibc has it only for internal use (and musl uses a
direct syscall in that case rather than a function call), not for
exposing it to applications.
in case of mmap-obtained chunks, end points past the end of the
mapping and reading it may fault. since the value is not needed until
after the conditional, move the access to prevent invalid reads.
they were accidentally exposed under just baseline POSIX, which is a
big namespace pollution issue. thankfully glibc only exposes them
under _GNU_SOURCE, not under any of its other options, so omitting
the pollution in the default _BSD_SOURCE profile does not hurt
application compatibility at all.
previously the names were exposed as key/seq with _GNU_SOURCE and
__ipc_perm_key/__ipc_perm/seq otherwise, whereas glibc always uses
__key and __seq for the names. thus, the old behavior never matched
glibc, and the new behavior always does, regardless of feature test
macros.
for now, i'm leaving the renaming here in sys/ipc.h where it's easy to
change globally for all archs, in case something turns out to be
wrong, but eventually the names could just be incorporated directly
into the bits headers for each arch and the renaming removed.
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.
previously, everything was going through an intermediate conversion to
long double, which caused the extern __fpclassifyl function to get
invoked, preventing virtually all optimizations of these operations.
with the new code, tests on constant float or double arguments compile
to a constant 0 or 1, and tests on non-constant expressions are
efficient. I may later add support for __builtin versions on compilers
that support them.
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.
due to some historical oddity, these are considered libc headers
rather than kernel headers. the kernel used to provide them too, but
it seems modern kernels do not install them, so let's just do the
easiest thing and provide them. stripped-down versions provided by
John Spencer.
apparently recent gcc versions have intentionally broken the
traditional definition by treating it as a non-constant expression.
the traditional definition may also be problematic for c++ programs.
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, a few BSD features were enabled only by _BSD_SOURCE, not
by _GNU_SOURCE. since _BSD_SOURCE is default in the absence of other
feature test macros, this made adding _GNU_SOURCE to a project not a
purely additive feature test macro; it actually caused some features
to be suppressed.
most of the changes made by this patch actually bring musl in closer
alignment with the glibc behavior for _GNU_SOURCE. the only exceptions
are the added visibility of functions like strlcpy which were BSD-only
due to being disliked/rejected by glibc maintainers. here, I feel the
consistency of having _GNU_SOURCE mean "everything", and especially
the property of it being purely additive, are more valuable than
hiding functions which glibc does not have.
most importantly, the format/scan macros for the [u]int_fast16_t and
[u]int_fast32_t types were defined incorrectly assuming these types
would match the native word/pointer size. this is incorrect on any
64-bit system; the "fast" types for 16- and 32-bit integers are simply
int.
another issue which was "only a warning" (despite being UB) is that
the choice of "l" versus "ll" was incorrect for 64-bit types on 64-bit
machines. while it would "work" to always use "long long" for 64-bit
types, we use "long" on 64-bit machines to match what glibc does and
what the ABI documents recommend. the macro definitions were probably
right in very old versions of musl, but became wrong when we aligned
most closely with the 'standard' ABI. checking UINTPTR_MAX is an easy
way to get the system wordsize without pulling in new headers.
finally, the useless __PRIPTR macro to allow the underlying type of
[u]intptr_t to vary has been removed. we are using "long" on all
targets, and thankfully this matches what glibc does, so I do not
envision ever needing to change it. thus, the "l" has just been
incorporated directly in the strings.
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.
the missing check did not affect the default profile, since it has
both _XOPEN_SOURCE and _BSD_SOURCE defined, but it did break programs
which explicitly define _BSD_SOURCE, causing it to be the only feature
test macro present.
these structures are purely for use by trace/debug tools and tools
working with core files. the definition of fpregset_t, which was
previously here, has been removed because it was wrong; fpregset_t
should be the type used in mcontext_t, not the type used in
ptrace/core stuff.
aside from microblaze, these should be roughly correct for all archs
now. some misc junk macros and typedefs are missing, which should
probably be added for max compatibility with trace/debug tools.
it should now really match the kernel. some of the removed padding
corresponded to the difference between user and kernel sigset_t. the
space at the end was redundant with the uc_mcontext member and seems
to have been added as a result of misunderstanding glibc's definition
versus the kernel's.
Rich Felker
rofl0r