Rich Felker
1ef37aa00e
we don't actually support building asm source files as thumb1, but
it's possible that the condition __ARM_ARCH>=5 would be false on old
compilers that did not define __ARM_ARCH at all. avoiding that would
require enumerating all of the possible __ARM_ARCH_*__ macros for
testing.
as noted in commit 05870abeaa, mov lr,pc
is not valid for saving a return address when in thumb mode. since
this code is a hot path (dynamic TLS access), don't do the out-of-line
bl->bx chaining to save the return value; instead, use the fact that
this file is preprocessed asm to add the missing thumb bit with an add
in place of the mov.
the change here does not affect builds for ISA levels new enough to
have a thread pointer read instruction, or for armv5 and later as long
as the compiler properly defines __ARM_ARCH, or for any build as arm
(not thumb) code. it's likely that it makes no difference whatsoever
to any present-day practical build environments, but nonetheless now
it's safe.
as an alternative, we could just assume __thumb__ implies availability
of blx since we don't support building asm source files as thumb1. I
didn't do that in order to avoid having a wrong assumption here if
that ever changes.
musl libc
musl, pronounced like the word "mussel", is an MIT-licensed
implementation of the standard C library targetting the Linux syscall
API, suitable for use in a wide range of deployment environments. musl
offers efficient static and dynamic linking support, lightweight code
and low runtime overhead, strong fail-safe guarantees under correct
usage, and correctness in the sense of standards conformance and
safety. musl is built on the principle that these goals are best
achieved through simple code that is easy to understand and maintain.
The 1.1 release series for musl features coverage for all interfaces
defined in ISO C99 and POSIX 2008 base, along with a number of
non-standardized interfaces for compatibility with Linux, BSD, and
glibc functionality.
For basic installation instructions, see the included INSTALL file.
Information on full musl-targeted compiler toolchains, system
bootstrapping, and Linux distributions built on musl can be found on
the project website:
http://www.musl-libc.org/