[Bug 211924] lib/libc/sys/mmap_test:mmap_truncate_signal fails with SIGSEGV instead of SIGBUS

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=211924

--- Comment #10 from commit-hook at freebsd.org ---
A commit references this bug:

Author: kib
Date: Fri Sep 27 18:43:39 UTC 2019
New revision: 352807
URL: https://svnweb.freebsd.org/changeset/base/352807

Log:
  Improve MD page fault handlers.

  Centralize calculation of signal and ucode delivered on unhandled page
  fault in new function vm_fault_trap().  MD trap_pfault() now almost
  always uses the signal numbers and error codes calculated in
  consistent MI way.

  This introduces the protection fault compatibility sysctls to all
  non-x86 architectures which did not have that bug, but apparently they
  were already much more wrong in selecting delivered signals on
  protection violations.

  Change the delivered signal for accesses to mapped area after the
  backing object was truncated.  According to POSIX description for
  mmap(2):
     The system shall always zero-fill any partial page at the end of an
     object. Further, the system shall never write out any modified
     portions of the last page of an object which are beyond its
     end. References within the address range starting at pa and
     continuing for len bytes to whole pages following the end of an
     object shall result in delivery of a SIGBUS signal.

     An implementation may generate SIGBUS signals when a reference
     would cause an error in the mapped object, such as out-of-space
     condition.
  Adjust according to the description, keeping the existing
  compatibility code for SIGSEGV/SIGBUS on protection failures.

  For situations where kernel cannot handle page fault due to resource
  limit enforcement, SIGBUS with a new error code BUS_OBJERR is
  delivered.  Also, provide a new error code SEGV_PKUERR for SIGSEGV on
  amd64 due to protection key access violation.

  vm_fault_hold() is renamed to vm_fault().  Fixed some nits in
  trap_pfault()s like mis-interpreting Mach errors as errnos.  Removed
  unneeded truncations of the fault addresses reported by hardware.

  PR:   211924
  Reviewed by:  alc
  Discussed with:       jilles, markj
  Sponsored by: The FreeBSD Foundation
  MFC after:    1 week
  Differential revision:        https://reviews.freebsd.org/D21566

Changes:
  head/sys/amd64/amd64/trap.c
  head/sys/amd64/vmm/vmm.c
  head/sys/arm/arm/trap-v4.c
  head/sys/arm/arm/trap-v6.c
  head/sys/arm64/arm64/trap.c
  head/sys/i386/i386/trap.c
  head/sys/kern/sys_process.c
  head/sys/mips/mips/trap.c
  head/sys/powerpc/powerpc/trap.c
  head/sys/riscv/riscv/trap.c
  head/sys/sparc64/sparc64/trap.c
  head/sys/sys/signal.h
  head/sys/vm/vm_extern.h
  head/sys/vm/vm_fault.c
  head/sys/vm/vm_map.c
  head/sys/vm/vm_param.h

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