this flag for strong access ordering was added in linux v2.6.27
commit aba46c5027cb59d98052231b36efcbbde9c77a1d

the definitions didn't match the linux uapi headers.

a_ll/a_sc inline asm used 64bit register operands (%0) instead of 32bit
ones (%w0), this at least broke a_and_64 (which always cleared the top
32bit, leaking memory in malloc).

aarch64 provides ll/sc variants with acquire/release memory order,
freeing us from the need to have full barriers both before and after
the ll/sc operation. previously they were not used because the a_cas
can fail without performing a_sc, in which case half of the barrier
would be omitted. instead, define a custom version of a_cas for
aarch64 which uses a_barrier explicitly when aborting the cas
operation. aside from cas, other operations built on top of ll/sc are
not affected since they never abort but rather loop until they
succeed.

a split ll/sc version of the pointer-sized a_cas_p is also introduced
using the same technique.

patch by Szabolcs Nagy.

the files that used to come from extra src dirs under the arch dir
have all been removed or moved to appropriate places under the main
src tree.

commit f3ddd173, the dynamic linker
bootstrap overhaul, silently disabled the definition of __fpscr_values
in this file since libc.so's copy of __fpscr_values now comes from
crt_arch.h, the same place the public definition in the main program's
crt1.o ultimately comes from. remove this file which is no longer in
use.

all such arch-specific translation units are being moved to
appropriate arch dirs under the main src tree.

previously powerpc had a_cas defined in terms of its native ll/sc
style operations, but all other atomics were defined in terms of
a_cas. instead define a_ll and a_sc so the compiler can generate
optimized versions of all the atomic ops and perform better inlining
of a_cas.

extracting the result of the sc (stwcx.) instruction is rather awkward
because it's natively stored in a condition flag, which is not
representable in inline asm. but even with this limitation the new
code still seems significantly better.

this commit mostly makes consistent things like spacing, function
ordering in atomic_arch.h, argument names, use of volatile, etc.
a_ctz_l was also removed from x86_64 since atomic.h provides it
automatically using a_ctz_64.

this commit mostly makes consistent things like spacing, function
ordering in atomic_arch.h, argument names, use of volatile, etc. the
fake 64-bit and/or atomics are also removed because the shared
atomic.h does a better job of implementing them; it avoids making two
atomic memory accesses when only one 32-bit half needs to be touched.

no major overhaul is needed or possible because x86 actually has
native versions of all the usual atomic operations, rather than using
ll/sc or needing cas loops.

this is possible with the new build system that allows src/*/$(ARCH)/*
files which do not shadow a file in the parent directory, and yields a
more logical organization. eventually it will be possible to remove
arch/*/src from the build system.

switch to ll/sc model so that new atomic.h can provide optimized
versions of all the atomic primitives without needing an ll/sc loop
written in asm for each one.

all isa levels which use ldrex/strex now use the inline ll/sc model
even if the type of barrier to use is not known until runtime (v6).
the cas model is only used for arm v5 and earlier, and it has been
optimized to make the call via inline asm with custom constraints
rather than as a C function call.

sh needs runtime-selected atomic backends since there are a number of
supported models that use non-forwards-compatible (non-smp-compatible)
atomic mechanisms. previously, the code paths for this were highly
inefficient since they involved C function calls with multiple
branches in the callee and heavy spills in the caller. the new code
performs calls the runtime-selected asm fragment from inline asm with
extremely minimal clobbers, rather than using a function call.

for the sh4a case where the atomic mechanism is known and there is no
forward-compatibility issue, the movli.l and movco.l instructions are
provided as a_ll and a_sc, allowing the new shared atomic.h to
generate efficient inline versions of all the basic atomic operations
without needing a cas loop.

rather than having each arch provide its own atomic.h, there is a new
shared atomic.h in src/internal which pulls arch-specific definitions
from arc/$(ARCH)/atomic_arch.h. the latter can be extremely minimal,
defining only a_cas or new ll/sc type primitives which the shared
atomic.h will use to construct everything else.

this commit avoids making heavy changes to the individual archs'
atomic implementations. definitions which are identical or
near-identical to what the new shared atomic.h would produce have been
removed, but otherwise the changes made are just hooking up the
arch-specific files to the new infrastructure. major changes to take
advantage of the new system will come in subsequent commits.

commit 2f853dd6 failed to change the
test for -include vis.h support to use $srcdir, so vis.h was always
disabled by configure for out-of-tree builds.

otherwise C declarations are included into preprocessed (.S) asm
source files, producing errors from the assembler.

the lib dir is automatically created if needed by the out-of-tree
build logic, and now that all generated files are in obj and lib,
deleting them is much simpler. using "rm -rf" is also more thorough,
as it picks up object files that were left around from source files
that no longer exist or which are no longer to be used because an
arch-specific replacement file was added or removed.

also clean up duplication of CFLAGS passing to assembler.

as of commit af21a82c, .sub files are
no longer in use. removing the makefile machinery to handle them not
only cleans up and simplifies the makefile, but also significantly
reduces make's startup time.

commit 2f853dd6 failed to replicate
the old makefile logic that caused arch/arm/src/arm/atomics.s to be
built. since this was the only .s file under arch/*/src, rather than
trying to reproduce the old logic, I'm just moving it up a level and
adjusting the glob pattern in the makefile to catch it. eventually
arch/*/src will probably be removed in favor of moving all these files
to appropriate src/*/$(ARCH) locations.

the __SOFTFP__ macro which was wrongly being used does not reflect the
ABI (arm vs armhf) but just the availability of floating point
instructions/registers, so -mfloat-abi=softfp was wrongly being
treated as armhf. __ARM_PCS_VFP is the correct predefined macro to
check for the armhf EABI variant. this macro usage was corrected for
the build process in commit 4918c2bb
but reloc.h was apparently overlooked at the time.

this makes it possible to inline them with LTO, and is the simplest
approach to eliminating the use of .sub files.

this also makes VFP sqrt available for use with the standard EABI
(plain arm rather than armhf subarch) when libc is built with
-mfloat-abi=softfp. the same could have been done for fabs, but when
the argument and return value are in integer registers, moving to VFP
registers and back is almost certainly more costly than a simple
integer operation.

this depends on commit 9f5eb779, which
made it possible to use a .c file for arch-specific replacements, and on
commit 2f853dd6, the out-of-tree build
support, which made it so that src/*/$(ARCH)/* 'replacement' files get
used even if they don't match the base name of a .c file in the parent
directory.

this allows the rules for .o and .lo files to be identical, with -fPIC
and -DSHARED added for .lo files via target-specific variable append.
this is arguably cleaner now and will allow more cleanup and removal
of redundant rule bodies after other prerequisite changes are made.

previously, replacement files provided in $(ARCH) dirs under src/ had
to be .s files. in order to replace a file with C source, an empty .s
file was needed there to suppress the original file, and a separate .c
file was needed in arch/$(ARCH)/src/.

support for .S is new and is aimed at short-term use eliminating .sub
files. asm source files are still expected not to make any heavy
preprocessor use, just simple conditionals on subarch. eventually most
affected files may be replaced with C source files with minimal inline
asm instead of asm source files.

Programs such as iptables depend on these constants, which can also
be found defined in other libcs.

Since only TCP_* is reserved as part of tcp.h's namespace, we hide
them behind _BSD_SOURCE (and therefore _DEFAULT_SOURCE) to expose
them by default, but keep it standard conforming.

The return value of if_nametoindex is unsigned; it should return 0
on error.

this change adds support for building musl outside of the source
tree. the implementation is similar to autotools where running
configure in a different directory creates config.mak in the current
working directory and symlinks the makefile, which contains the
logic for creating all necessary directories and resolving paths
relative to the source directory.

to support both in-tree and out-of-tree builds with implicit make
rules, all object files are now placed into a separate directory.

apparently the .gpword directive does not work reliably with local
text labels; values produced were offset by 64k from the correct
value, resulting in incorrect computation of the got pointer at
runtime. instead, use an external label so that the assembler does not
munge the relocation; the linker will then get it right.

commit 6fef8caf exposed this issue by
removing the old, non-PIE-compatible handwritten crt1.s, which was not
affected. presumably mips PIE executables (using Scrt1.o produced from
crt_arch.h) were already affected at the time.

at least gcc 4.7 claims c++11 support but does not accept the alignas
keyword, causing breakage when stddef.h is included in c++11 mode.
instead, prefer using __attribute__((__aligned__)) on any compiler
with GNU extensions, and only use the alignas keyword as a fallback
for other C++ compilers.

C code should not be affected by this patch.

previously, getdelim was allocating twice the space needed every time
it expanded its buffer to implement exponential buffer growth (in
order to avoid quadratic run time). however, this doubling was
performed even when the final buffer length needed was already known,
which is the common case that occurs whenever the delimiter is in the
FILE's buffer.

this patch makes two changes to remedy the situation:

1. over-allocation is no longer performed if the delimiter has already
been found when realloc is needed.

2. growth factor is reduced from 2x to 1.5x to reduce the relative
excess allocation in cases where the delimiter is not initially in the
buffer, including unbuffered streams.

in theory these changes could lead to quadratic time if the same
buffer is reused to process a sequence of lines successively
increasing in length, but once this length exceeds the stdio buffer
size, the delimiter will not be found in the buffer right away and
exponential growth will still kick in.