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  1. 11 4月, 2019 1 次提交
    • R
      overhaul i386 syscall mechanism not to depend on external asm source · 22e5bbd0
      由 Rich Felker 提交于 
      this is the first part of a series of patches intended to make
__syscall fully self-contained in the object file produced using
syscall.h, which will make it possible for crt1 code to perform
syscalls.

the (confusingly named) i386 __vsyscall mechanism, which this commit
removes, was introduced before the presence of a valid thread pointer
was mandatory; back then the thread pointer was setup lazily only if
threads were used. the intent was to be able to perform syscalls using
the kernel's fast entry point in the VDSO, which can use the sysenter
(Intel) or syscall (AMD) instruction instead of int $128, but without
inlining an access to the __syscall global at the point of each
syscall, which would incur a significant size cost from PIC setup
everywhere. the mechanism also shuffled registers/calling convention
around to avoid spills of call-saved registers, and to avoid
allocating ebx or ebp via asm constraints, since there are plenty of
broken-but-supported compiler versions which are incapable of
allocating ebx with -fPIC or ebp with -fno-omit-frame-pointer.

the new mechanism preserves the properties of avoiding spills and
avoiding allocation of ebx/ebp in constraints, but does it inline,
using some fairly simple register shuffling, and uses a field of the
thread structure rather than global data for the vdso-provided syscall
code address.

for now, the external __syscall function is refactored not to use the
old __vsyscall so it can be kept, but the intent is to remove it too.
      22e5bbd0
  3. 10 4月, 2019 2 次提交
    • R
      release 1.1.22 · e97681d6
      由 Rich Felker 提交于
      e97681d6
    • R
      in membarrier fallback, allow for possibility that sigaction fails · a01ff71f
      由 Rich Felker 提交于 
      this is a workaround to avoid a crashing regression on qemu-user when
dynamic TLS is installed at dlopen time. the sigaction syscall should
not be able to fail, but it does fail for implementation-internal
signals under qemu user-level emulation if the host libc qemu is
running under reserves the same signals for implementation-internal
use, since qemu makes no provision to redirect/emulate them. after
sigaction fails, the subsequent tkill would terminate the process
abnormally as the default action.

no provision to account for membarrier failing is made in the dynamic
linker code that installs new TLS. at the formal level, the missing
barrier in this case is incorrect, and perhaps we should fail the
dlopen operation, but in practice all the archs we support (and
probably all real-world archs except alpha, which isn't yet supported)
should give the right behavior with no barrier at all as a consequence
of consume-order properties.

in the long term, this workaround should be supplemented or replaced
by something better -- a different fallback approach to ensuring
memory consistency, or dynamic allocation of implementation-internal
signals. the latter is appealing in that it would allow cancellation
to work under qemu-user too, and would even allow many levels of
nested emulation.
      a01ff71f
  5. 06 4月, 2019 2 次提交
  7. 04 4月, 2019 1 次提交
    • D
      fix unintended global symbols in atanl.c · 81868803
      由 Dan Gohman 提交于 
      Mark atanhi, atanlo, and aT in atanl.c as static, as they're not
intended to be part of the public API.

These are already static in the LDBL_MANT_DIG == 64 code, so this
patch is just making the LDBL_MANT_DIG == 113 code do the same thing.
      81868803
  9. 02 4月, 2019 3 次提交
  11. 01 4月, 2019 1 次提交
    • R
      implement priority inheritance mutexes · 54ca6779
      由 Rich Felker 提交于 
      priority inheritance is a feature to mitigate priority inversion
situations, where a execution of a medium-priority thread can
unboundedly block forward progress of a high-priority thread when a
lock it needs is held by a low-priority thread.

the natural way to do priority inheritance would be with a simple
futex flag to donate the calling thread's priority to a target thread
while it waits on the futex. unfortunately, linux does not offer such
an interface, but instead insists on implementing the whole locking
protocol in kernelspace with special futex commands that exist solely
for the purpose of doing PI mutexes. this would require the entire
"trylock" logic to be duplicated in the timedlock code path for PI
mutexes, since, once the previous lock holder releases the lock and
the futex call returns, the lock is already held by the caller.
obviously such code duplication is undesirable.

instead, I've made the PI timedlock success path set the mutex lock
count to -1, which can be thought of as "not yet complete", since a
lock count of 0 is "locked, with no recursive references". a simple
branch in a non-hot path of pthread_mutex_trylock can then see and act
on this state, skipping past the code that would check and take the
lock to the same code path that runs after the lock is obtained for a
non-PI mutex.

because we're forced to let the kernel perform the actual lock and
unlock operations whenever the mutex is contended, we have to patch
things up when it does the wrong thing:

1. the lock operation is not aware of whether the mutex is
   error-checking, so it will always fail with EDEADLK rather than
   deadlocking.

2. the lock operation is not aware of whether the mutex is robust, so
   it will successfully obtain mutexes in the owner-died state even if
   they're non-robust, whereas this operation should deadlock.

3. the unlock operation always sets the lock value to zero, whereas
   for robust mutexes, we want to set it to a special value indicating
   that the mutex obtained after its owner died was unlocked without
   marking it consistent, so that future operations all fail with
   ENOTRECOVERABLE.

the first of these is easy to solve, just by performing a futex wait
on a dummy futex address to simulate deadlock or ETIMEDOUT as
appropriate. but problems 2 and 3 interact in a nasty way. to solve
problem 2, we need to back out the spurious success. but if waiters
are present -- which we can't just ignore, because even if we don't
want to wake them, the calling thread is incorrectly inheriting their
priorities -- this requires using the kernel's unlock operation, which
will zero the lock value, thereby losing the "owner died with lock
held" state.

to solve these problems, we overload the mutex's waiters field, which
is unused for PI mutexes since they don't call the normal futex wait
functions, as an indicator that the PI mutex is permanently
non-lockable. originally I wanted to use the count field, but there is
one code path that needs to access this flag without synchronization:
trylock's CAS failure path needs to be able to decide whether to fail
with EBUSY or ENOTRECOVERABLE, the waiters field is already treated as
a relaxed-order atomic in our memory model, so this works out nicely.
      54ca6779
  13. 30 3月, 2019 1 次提交
    • R
      clean up access to mutex type in pthread_mutex_trylock · 2142cafd
      由 Rich Felker 提交于 
      there was no point in masking off the pshared bit when first loading
the type, since every subsequent access involves a mask anyway. not
masking it may avoid a subsequent load to check the pshared flag, and
it's just simpler.
      2142cafd
  15. 22 3月, 2019 3 次提交
  17. 15 3月, 2019 1 次提交
    • R
      fix crash/out-of-bound read in sscanf · 8f12c4e1
      由 Rich Felker 提交于 
      commit d6c855ca caused this
"regression", though the behavior was undefined before, overlooking
that f->shend=0 was being used as a sentinel for "EOF" status (actual
EOF or hitting the scanf field width) of the stream helper (shgetc)
functions.

obviously the shgetc macro could be adjusted to check for a null
pointer in addition to the != comparison, but it's the hot path, and
adding extra code/branches to it begins to defeat the purpose.

so instead of setting shend to a null pointer to block further reads,
which no longer works, set it to the current position (rpos). this
makes the shgetc macro work with no change, but it breaks shunget,
which can no longer look at the value of shend to determine whether to
back up. Szabolcs Nagy suggested a solution which I'm using here:
setting shlim to a negative value is inexpensive to test at shunget
time, and automatically re-trips the cnt>=shlim stop condition in
__shgetc no matter what the original limit was.
      8f12c4e1
  19. 14 3月, 2019 22 次提交
  21. 13 3月, 2019 3 次提交
    • R
      handle labels with 8-bit byte values in dn_skipname · 2a0ff45b
      由 Ryan Fairfax 提交于 
      The original logic considered each byte until it either found a 0
value or a value >= 192. This means if a string segment contained any
byte >= 192 it was interepretted as a compressed segment marker even
if it wasn't in a position where it should be interpretted as such.

The fix is to adjust dn_skipname to increment by each segments size
rather than look at each character. This avoids misinterpretting
string segment characters by not considering those bytes.
      2a0ff45b
    • J
      fix POSIX_FADV_DONTNEED/_NOREUSE on s390x · 4b125dd4
      由 Jonathan Neuschäfer 提交于 
      On s390x, POSIX_FADV_DONTNEED and POSIX_FADV_NOREUSE have different
values than on all other architectures that Linux supports.

Handle this difference by wrapping their definitions in
include/fcntl.h in #ifdef, so that arch/s390x/bits/fcntl.h can
override them.
      4b125dd4
    • R
      expose TSVTX unconditionally in tar.h · 81221e13
      由 Rich Felker 提交于 
      as noted in Austin Group issue #1236, the XSI shading for TSVTX is
misplaced in the html version of the standard; it was only supposed to
be on the description text. the intent was that the definition always
be visible, which is reflected in the pdf version of the standard.

this reverts commits d93c0740 and
729fef0a.
      81221e13