Crossing 2GB boundaries with indirect calls and jumps can use more
branch prediction resources on Intel Golden Cove CPU (see the
"Misprediction for Branches >2GB" section in Intel 64 and IA-32
Architectures Optimization Reference Manual.) There is visible
performance improvement on workloads with many PLT calls when executable
and shared libraries are mmapped below 2GB. Add the Prefer_MAP_32BIT_EXEC
bit so that mmap will try to map executable or denywrite pages in shared
libraries with MAP_32BIT first.
NB: Prefer_MAP_32BIT_EXEC reduces bits available for address space
layout randomization (ASLR), which is always disabled for SUID programs
and can only be enabled by the tunable, glibc.cpu.prefer_map_32bit_exec,
or the environment variable, LD_PREFER_MAP_32BIT_EXEC. This works only
between shared libraries or between shared libraries and executables with
addresses below 2GB. PIEs are usually loaded at a random address above
4GB by the kernel.
Remove the LD_PREFER_MAP_32BIT_EXEC environment variable support since
the first PT_LOAD segment is no longer executable due to defaulting to
-z separate-code.
This fixes [BZ #28656].
Reviewed-by: Florian Weimer <fweimer@redhat.com>
I used these shell commands:
../glibc/scripts/update-copyrights $PWD/../gnulib/build-aux/update-copyright
(cd ../glibc && git commit -am"[this commit message]")
and then ignored the output, which consisted lines saying "FOO: warning:
copyright statement not found" for each of 6694 files FOO.
I then removed trailing white space from benchtests/bench-pthread-locks.c
and iconvdata/tst-iconv-big5-hkscs-to-2ucs4.c, to work around this
diagnostic from Savannah:
remote: *** pre-commit check failed ...
remote: *** error: lines with trailing whitespace found
remote: error: hook declined to update refs/heads/master
This patch consolidates all Linux mmap implementations on default
sysdeps/unix/sysv/linux/mmap{64}.c one. To accomodate all required
architecture specific requeriments a new internal header is created
(mmap_internal.h) where each architecture add its specific code
requirements. Currently only x86_64 (to define MMAP_PREPARE to add
MAP_32BITS), s390 (which have a different kernel ABI for mmap), m68k
(which have variable minimum page sizes), and MIPS n32 (which zero
extend the offset to handle negative one correctly) redefine the new
header.
The patch also fixes BZ#21270 where default mmap64 on architectures
which uses mmap2 silent truncates large offsets value (larger than
1 << (page shift + 8 * sizeof (off_t)) or 1<<44 on architectures with
4096 bytes page size). The new consolidate implementation returns
EINVAL as allowed by POSIX.
It also adds a tests for on current tst-mmap-offset one. I have run
a full make check on x86_64, x86_64-32, i686, aarch64, armhf, powerpc,
powerpc64le, sparc64, and sparcv9 without any regressions. I also ran
some basic tests (tst-mmap-offset) on sh4, m68k, and on qemu simulated
MIPS32 and MIPS64.
[BZ #21270]
* posix/tst-mmap-offset.c (do_prepare): New function.
(do_test): Rename to do_test_bz18877 and use FAIL_RET.
(do_test_bz21270): New function.
* sysdeps/unix/sysv/linux/aarch64/mmap.c: Remove file.
* sysdeps/unix/sysv/linux/arm/mmap.c: Remove file.
* sysdeps/unix/sysv/linux/generic/wordsize-32/mmap.c: Likewise.
* sysdeps/unix/sysv/linux/hppa/mmap.c: Likewise.
* sysdeps/unix/sysv/linux/i386/mmap.c: Likewise.
* sysdeps/unix/sysv/linux/m68k/mmap.S: Likewise.
* sysdeps/unix/sysv/linux/m68k/mmap64.c: Likewise.
* sysdeps/unix/sysv/linux/microblaze/mmap.S: Likewise.
* sysdeps/unix/sysv/linux/mips/mips32/mmap.c: Likewise.
* sysdeps/unix/sysv/linux/mips/mips64/n32/mmap.c: Likewise.
* sysdeps/unix/sysv/linux/mips/mips64/n64/mmap64.c: Likewise.
* sysdeps/unix/sysv/linux/s390/s390-32/mmap.S: Likewise.
* sysdeps/unix/sysv/linux/s390/s390-32/mmap64.S: Likewise.
* sysdeps/unix/sysv/linux/s390/s390-64/mmap.S: Likewise.
* sysdeps/unix/sysv/linux/wordsize-64/mmap.c: Likewise.
* sysdeps/unix/sysv/linux/wordsize-64/mmap64.c: Likewise.
* sysdeps/unix/sysv/linux/x86_64/64/mmap.c: Likewise.
* sysdeps/unix/sysv/linux/mmap_internal.h: New file.
* sysdeps/unix/sysv/linux/m68k/mmap_internal.h: Likewise.
* sysdeps/unix/sysv/linux/mips/mips64/n32/mmap_internal.h: Likewise.
* sysdeps/unix/sysv/linux/s390/mmap_internal.h: Likewise.
* sysdeps/unix/sysv/linux/x86_64/64/mmap_internal.h: Likewise.
* sysdeps/unix/sysv/linux/mips/mips64/n64/syscalls.list: Remove mmap
from auto-generation list.
* sysdeps/unix/sysv/linux/mips/mips64/n32/syscalls.list: Likewise.
* sysdeps/unix/sysv/linux/wordsize-64/syscalls.list: Likewise.
* sysdeps/unix/sysv/linux/mmap.c: New file.
* sysdeps/unix/sysv/linux/mmap64.c (__mmap64): Add check for invalid
offsets and support for mmap2 syscall.
