[PATCH v2 0/6] elf: Use mmap to map in section contents

[H.J. Lu]

Changes in v2:

1. Don't hard-code BFD_JUMP_TABLE_COPY in bfd so that elf-bfd.h can be
included in libbfd.c.
2. Change the --with-mmap default to true.
3. Check USE_MMAP instead of HAVE_MMAP.
4. Remove the asize parameter to _bfd_mmap_readonly_tracked.
5. Add contents_addr and contents_size to bfd_elf_section_data.
6. Rename _bfd_link_keep_memory to _bfd_elf_link_keep_memory.

---
We can use mmap to map in ELF section contents, instead of copying them
into memory by hand.  We don't need to cache symbol nor relocation tables
if they are mapped in.  Data to link the 3.5GB clang executable in LLVM
17 debug build on Linux/x86-64 with 32GB RAM is:

		stdio		mmap		improvement
user		86.73		87.02		-0.3%
system		9.55		9.21		3.6%
total		100.40		97.66		0.7%
maximum set(GB)	17.34		13.14		24%
page faults	4047667		3042877		25%

and data to link the 275M cc1plus executable in GCC 14 stage 1 build is:

user		5.41		5.44		-0.5%
system		0.80		0.76		5%
total		6.25		6.26		-0.2%
maximum set(MB)	1323		968		27%
page faults	323451		236371		27%

Data shows that these won't improve the single copy linker performance.
But they improve the overall system performance when linker is used by
reducing linker memory usage and page faults.  They allow more parallel
linker jobs on LLVM debug build.

Here is a quote from Noah Goldstein: "on a large project they are an
extremely large speedup".
H.J. Lu (6):
  bfd: Don't hard-code BFD_JUMP_TABLE_COPY
  bfd: Change the --with-mmap default to true
  elf: Use mmap to map in read-only sections
  elf: Add _bfd_elf_mmap_section and _bfd_elf_munmap_section_contents
  elf: Use mmap to map in symbol and relocation tables
  elf: Don't cache symbol nor relocation tables with mmap

 bfd/aout-target.h   |   3 +
 bfd/bfd-in2.h       |  30 +++++-
 bfd/bfd.c           |  17 +++
 bfd/bfdio.c         |  16 +--
 bfd/bfdwin.c        |   8 +-
 bfd/cache.c         |  11 +-
 bfd/coff-rs6000.c   |   2 +
 bfd/coffcode.h      |   2 +
 bfd/compress.c      |   2 +-
 bfd/configure       |   2 +-
 bfd/configure.ac    |   2 +-
 bfd/elf-bfd.h       |  25 ++++-
 bfd/elf-eh-frame.c  |   4 +-
 bfd/elf-sframe.c    |   4 +-
 bfd/elf.c           | 253 ++++++++++++++++++++++++++++++++++++--------
 bfd/elf32-i386.c    |   8 +-
 bfd/elf64-x86-64.c  |  12 +--
 bfd/elfcode.h       |   7 +-
 bfd/elflink.c       | 134 ++++++++++++++++-------
 bfd/elfxx-target.h  |   8 +-
 bfd/elfxx-x86.c     |   7 +-
 bfd/elfxx-x86.h     |   1 +
 bfd/libbfd-in.h     |  33 +++++-
 bfd/libbfd.c        | 249 ++++++++++++++++++++++++++++++++++++++++++-
 bfd/libbfd.h        |  37 ++++++-
 bfd/libecoff.h      |   3 +
 bfd/linker.c        |  35 ------
 bfd/lynx-core.c     |   2 +-
 bfd/mach-o-target.c |   1 +
 bfd/mmo.c           |   1 +
 bfd/opncls.c        |  29 ++++-
 bfd/plugin.c        |   1 +
 bfd/ppcboot.c       |   1 +
 bfd/section.c       |   9 +-
 bfd/som.c           |   1 +
 bfd/targets.c       |   2 +-
 bfd/vms-alpha.c     |   1 +
 37 files changed, 776 insertions(+), 187 deletions(-)

-- 
2.44.0