Commit Graph

6 Commits

Author SHA1 Message Date
Fangrui Song 07f8daf05e [ELF] Simplify RelRo, TLS, NOBITS section ranks and make RW PT_LOAD start with RelRo
Old: PT_LOAD(.data | PT_GNU_RELRO(.data.rel.ro .bss.rel.ro) | .bss)
New: PT_LOAD(PT_GNU_RELRO(.data.rel.ro .bss.rel.ro) | .data .bss)

The placement of | indicates page alignment caused by PT_GNU_RELRO. The
new layout has simpler rules and saves space for many cases.

Old size: roundup(.data) + roundup(.data.rel.ro)
New size: roundup(.data.rel.ro + .bss.rel.ro) + .data

Other advantages:

* At runtime the 3 memory mappings decrease to 2.
* start(PT_TLS) = start(PT_GNU_RELRO) = start(RW PT_LOAD). This
  simplifies binary manipulation tools.
  GNU strip before 2.31 discards PT_GNU_RELRO if its
  address is not equal to the start of its associated PT_LOAD.
  This has been fixed by https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=f2731e0c374e5323ce4cdae2bcc7b7fe22da1a6f
  But with this change, we will be compatible with GNU strip before 2.31
* Before, .got.plt (non-relro by default) was placed before .got (relro
  by default), which made it impossible to have _GLOBAL_OFFSET_TABLE_
  (start of .got.plt on x86-64) equal to the end of .got (R_GOT*_FROM_END)
  (https://bugs.llvm.org/show_bug.cgi?id=36555). With the new ordering, we
  can improve on this regard if we'd like to.

Reviewers: ruiu, espindola, pcc

Subscribers: emaste, arichardson, llvm-commits, joerg, jdoerfert

Differential Revision: https://reviews.llvm.org/D56828

llvm-svn: 356117
2019-03-14 03:47:45 +00:00
Rui Ueyama cd7a415938 Use log to print out a verbose message.
llvm-svn: 324688
2018-02-09 00:15:12 +00:00
Peter Smith cbc9bb9ffd [ELF] Reduce size of ELF file produced by test
We only need to exceed 128 Megabytes to provoke the generation of a range
extension thunk. This brings the file size down to just over 128 Megabytes.

llvm-svn: 320821
2017-12-15 15:30:00 +00:00
Rafael Espindola 9b332d997f Delete a really large test output.
llvm-svn: 320818
2017-12-15 14:56:01 +00:00
Peter Smith cf354873c1 [ELF] Complete implementation of --fix-cortex-a53-843419
This patch provides the mechanism to fix instances of the instruction
sequence that may trigger the cortex-a53 843419 erratum. The fix is
provided by an alternative instruction sequence to remove one of the
erratum conditions. To reach this alternative instruction sequence we
replace the original instruction with a branch to the alternative
sequence. The alternative sequence is responsible for branching back to
the original.

As there is only erratum to fix the implementation is specific to
AArch64 and the specific erratum conditions. It should be generalizable
to other targets and erratum if needed.

Differential Revision: https://reviews.llvm.org/D36749

llvm-svn: 320800
2017-12-15 10:32:34 +00:00
Peter Smith 732cd8cbef [ELF] Implement scanner for Cortex-A53 Erratum 843419
Add a new file AArch64ErrataFix.cpp that implements the logic to scan for
the Cortex-A53 Erratum 843419. This involves finding all the executable
code, disassembling the instructions that might trigger the erratum and
reporting a message if the sequence is detected.

At this stage we do not attempt to fix the erratum, this functionality
will be added in a later patch. See D36749 for proposal.

Differential Revision: https://reviews.llvm.org/D36742

llvm-svn: 319780
2017-12-05 15:59:05 +00:00