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the vdso symbol lookup code is based on the original 2011 patch by
Nicholas J. Kain, with some streamlining, pointer arithmetic fixes,
and one symbol version matching fix.
on the consumer side (clock_gettime), per-arch macros for the
particular symbol name and version to lookup are added in
syscall_arch.h, and no vdso code is pulled in on archs which do not
define these macros. at this time, vdso is enabled only on x86_64.
the vdso support at the dynamic linker level is no longer useful to
libc, but is left in place for the sake of debuggers (which may need
the vdso in the link map to find its functions) and possibly use with
at the end of successful pthread_once, there was a race window during
which another thread calling pthread_once would momentarily change the
state back from 2 (finished) to 1 (in-progress). in this case, the
status was immediately changed back, but with no wake call, meaning
that waiters which arrived during this short window could block
forever. there are two possible fixes. one would be adding the wake to
the code path where it was missing. but it's better just to avoid
reverting the status at all, by using compare-and-swap instead of
The mips arch is special in that it uses different RLIMIT_
numbers than other archs, so allow bits/resource.h to override
the default RLIMIT_ numbers (empty on all archs except mips).
Reported by orc.
it will be needed to implement some things in sysconf, and the syscall
can't easily be used directly because the x32 syscall uses the wrong
structure layout. the l (uncreative, for "linux") prefix is used since
the symbol name __sysinfo is already taken for AT_SYSINFO from the aux
the way the x32 override of this function works is also changed to be
simpler and avoid the useless jump instruction.
the syscall is deprecated (replaced by prlimit64) and does not work
correctly on x32. this change mildly increases size, but is likely
needed anyway for newer archs that might omit deprecated syscalls.
the previous handling of cases that could not fit in the 16-bit table
or which required non-constant results was extremely ugly and could
not scale. the new code remaps these keys into a contiguous range
that's efficient for a switch statement.
aside from potentially offering better performance, this change is
needed since the old coprocessor-based approach to barriers is
deprecated in arm v7, and some compilers/assemblers issue errors when
using the deprecated instruction for v7 targets.
the use of visibility at all is purely an optimization to avoid the
need for the caller to load the GOT register or similar to prepare for
a call via the PLT. there is no reason for these symbols to be
externally visible, so hidden works just as well as protected, and
using protected visibility is undesirable due to toolchain bugs and
the lack of testing it receives.
in particular, GCC's microblaze target is known to generate symbolic
relocations in the GOT for functions with protected visibility. this
in turn results in a dynamic linker which crashes under any nontrivial
usage that requires making a syscall before symbolic relocations are
modfl and sincosl were passing long double* instead of double*
to the wrapped double precision functions (on archs where long
double and double have the same size).
This is fixed now by using temporaries (this is not optimized
to a single branch so the generated code is a bit bigger).
Found by Morten Welinder.
to optimize the search, memchr is used to find the first occurrence of
the first character of the needle in the haystack before switching to
a search for the full needle. however, the number of characters
skipped by this first step were not subtracted from the haystack
length, causing memmem to search past the end of the haystack.
the subsequent rounding code assumes the end pointer (z) accurately
reflects the end of significance in the decimal expansion, but for
certain large integers, spurious trailing zero slots were left behind
when applying the binary exponent.
issue reported by Morten Welinder; the analysis of the cause was
performed by nsz, who also proposed this change.
the "m" constraint could give a memory reference with an offset that's
not compatible with ldrex/strex, so the arm-specific "Q" constraint is
this is perhaps not the optimal implementation; a_cas still compiles
to nested loops due to the different interface contracts of the kuser
helper cas function (whose contract this patch implements) and the
a_cas function (whose contract mimics the x86 cmpxchg). fixing this
may be possible, but it's more complicated and thus deferred until a
aside from improving performance and code size, this patch also
provides a means of producing binaries which can run on hardened
kernels where the kuser helpers have been disabled. however, at
present this requires producing binaries for armv6k or later, which
will not run on older cpus. a real solution to the problem of kernels
that omit the kuser helpers would be runtime detection, so that
universal binaries which run on all arm cpu models can also be
compatible with all kernel hardening profiles. robust detection
however is a much harder problem, and will be addressed at a later
in a sense this implementation is incomplete since it doesn't provide
the HWCAP_* macros for use with AT_HWCAP, which is perhaps the most
important intended usage case for getauxval. they will be added at a
the code to strip trailing zeros was only looking in the last slot for
up to 9 zeros, assuming that the rounding code had already removed
fully-zero slots from the end. however, this ignored cases where the
rounding code did not run at all, which occur when the value being
printed is exactly representable in the requested precision.
the simplest solution is to move the code that strips trailing zero
slots to run unconditionally, immediately after rounding, rather than
as the last step of rounding.
in cases where rounding caused a carry, the slot into which the carry
was taking place was unconditionally treated as valid, despite the
possibility that it could be a new slot prior to the beginning of the
existing non-rounded number. in theory this could lead to unbounded
runaway carry, but in order for that to happen, the whole
uninitialized buffer would need to have been pre-filled with 32-bit
integer values greater than or equal to 999999999.
patch based on proposed fix by Morten Welinder, who also discovered
and reported the bug.
the function itself was static, but the weak alias provided an
externally visible reference and thus prevented the dead code from
being omitted from the output. so this change actually reduces bloat
in mandatory static-linked code.
There are two changes here, both of which make sense to be done in a
- Remove hash from struct elem and compute it at runtime wherever
- Eliminate struct elem and use ENTRY directly.
As a result we cut down on the memory usage as each element in the
hash table now contains only an ENTRY not an ENTRY + size_t for the
hash. The downside is that the hash needs to be computed at runtime.
the size and alignment of struct hsearch_data are matched to the glibc
definition for binary compatibility. the members of the structure do
not match, which should not be a problem as long as applications
correctly treat the structure as opaque.
unlike the glibc implementation, this version of hcreate_r does not
require the caller to zero-fill the structure before use.
this issue mainly affects PIE binaries and execution of programs via
direct invocation of the dynamic linker binary: depending on kernel
behavior, in these cases the initial brk may be placed at at location
where it cannot be extended, due to conflicting adjacent maps.
when brk fails, mmap is used instead to expand the heap. in order to
avoid expensive bookkeeping for managing fragmentation by merging
these new heap regions, the minimum size for new heap regions
increases exponentially in the number of regions. this limits the
number of regions, and thereby the number of fixed fragmentation
points, to a quantity which is logarithmic with respect to the size of
virtual address space and thus negligible. the exponential growth is
tuned so as to avoid expanding the heap by more than approximately 50%
of its current total size.
the kernel entry point for syscalls on microblaze nominally saves and
restores all registers, and testing on qemu always worked since qemu
behaves this way too. however, the real kernel treats r3:r4 as a
potential 64-bit return value from the syscall function, and copies
both over top of the saved registers before returning to userspace.
thus, we need to treat r4 as always-clobbered.
now that thread pointer is initialized always, ssp canary
initialization can be done unconditionally. this simplifies
the ldso as it does not try to detect ssp usage, and the
init function itself as it is always called exactly once.
this also merges ssp init path for shared and static linking.
consistent use of braces in if/else structure, line length.
record phentsize in struct dso, so the phdrs can be easily
enumerated via it. simplify all functions enumerating phdrs
to require only struct dso. also merge find_map_range and
find_dso to kernel_mapped_dso function that does both tasks
during single phdr enumeration.
per the specification, the terminating null byte is counted.
this is the first step in an overhaul aimed at greatly simplifying and
optimizing everything dealing with thread-local state.
previously, the thread pointer was initialized lazily on first access,
or at program startup if stack protector was in use, or at certain
random places where inconsistent state could be reached if it were not
initialized early. while believed to be fully correct, the logic was
fragile and non-obvious.
in the first phase of the thread pointer overhaul, support is retained
(and in some cases improved) for systems/situation where loading the
thread pointer fails, e.g. old kernels.
some notes on specific changes:
- the confusing use of libc.main_thread as an indicator that the
thread pointer is initialized is eliminated in favor of an explicit
- sigaction no longer needs to ensure that the thread pointer is
initialized before installing a signal handler (this was needed to
prevent a situation where the signal handler caused the thread
pointer to be initialized and the subsequent sigreturn cleared it
again) but it still needs to ensure that implementation-internal
thread-related signals are not blocked.
- pthread tsd initialization for the main thread is deferred in a new
manner to minimize bloat in the static-linked __init_tp code.
- pthread_setcancelstate no longer needs special handling for the
situation before the thread pointer is initialized. it simply fails
on systems that cannot support a thread pointer, which are
- pthread_cleanup_push/pop now check for missing thread pointer and
nop themselves out in this case, so stdio no longer needs to avoid
the cancellable path when the thread pointer is not available.
a number of cases remain where certain interfaces may crash if the
system does not support a thread pointer. at this point, these should
be limited to pthread interfaces, and the number of such cases should
be fewer than before.
the external mmap function is heavy because it has to handle error
reporting that the kernel cannot do, and has to do some locking for
arcane race-condition-avoidance purposes. for allocating initial TLS,
we do not need any of that; the raw syscall suffices.
on i386, this change shaves off 13% of the size of .text for the empty
in general, we aim to always include the header that's declaring a
function before defining it so that the compiler can check that
additionally, the internal syscall.h declares __syscall_ret with a
visibility attribute to improve code generation for shared libc (to
prevent gratuitous GOT-register loads). this declaration should be
visible at the point where __syscall_ret is defined, too, or the
inconsistency could theoretically lead to problems at link-time.
in addition to the dbm functions (which we don't intent to implement
anyway), fmtmsg is still missing too. rather than adding exceptions I
think it's best just to avoid making the claim.
reduces the amount of news-like content on progress and development
direction and focuses on the present.
the text covering an ill-advised procedure for 'bootstrapping' a new
musl-based system in-place is removed. new information on targets and
compilers is added. formatting improved. the remaining text is
adjusted to cover both usage with musl-gcc on a non-musl-based system
and upgrading a musl-based system or toolchain.
otherwise a multilib compiler used with -mx32 will not be detected
in the previous changes, I missed the fact that both the prototype of
the sigaltstack function and the definition of ucontext_t depend on
like almost everything on mips, this is gratuitously different.
it's different at least on mips. mips version will be fixed in a
separate commit to show the change.
this was missed in the previous commit.
the excess space was unused and unintentional. this change does not
affect the ABI between applications and libc. while it does
theoretically affect linkage between third-party translation units
using jmp_buf as part of a structure, we've already changed jmp_buf at
least once on all archs, and problems were never observed, likely
because such usage would be very unusual. in any case it's best to get
things right now rather than making changes sometime during the 1.0.x
series or later.
this seems to have been copied erroneously from the arm version of the
file. it's fairly harmless but it's a mistake and better to fix now
on x32, this change allows programs which use syscall() with pointers
or 64-bit values as arguments to work correctly, i.e. without
truncation or incorrect sign extension. on all other supported archs,
syscall_arg_t is defined as long, so this change is a no-op.