[PATCH v12 1/6] elf: Use mmap to map in read-only sections

[Simon Marchi]

On 2024-03-17 08:19, H.J. Lu wrote:
> There are many linker input files in LLVM debug build with huge string
> sections.  All these string sections can be treated as read-only.  But
> linker copies all of them into memory which consumes huge amount of
> memory and slows down linker significantly.
> 
> Add _bfd_mmap_readonly_persistent and _bfd_mmap_readonly_temporary to
> mmap in reado-only sections with size >= 4 * page size.
> 
> NB: All string sections in valid ELF inputs must be null terminated.
> There is no need to terminate it again and string sections are mmapped
> as read-only.
> 
> 	* bfd.c (bfd_mmapped_entry): New.
> 	(bfd_mmapped): Likewise.
> 	(bfd): Add mmapped.
> 	* bfdwin.c (bfd_get_file_window): Use _bfd_pagesize.
> 	* cache.c (cache_bmmap): Remove pagesize_m1 and use pagesize_m1
> 	instead.
> 	* elf.c (bfd_elf_get_str_section): Call
> 	_bfd_mmap_readonly_persistent instead of _bfd_alloc_and_read.
> 	Don't terminate the string section again.
> 	(get_hash_table_data): Call _bfd_mmap_readonly_temporary and
> 	_bfd_munmap_readonly_temporary instead of _bfd_malloc_and_read
> 	and free.
> 	(_bfd_elf_get_dynamic_symbols): Call _bfd_mmap_readonly_persistent
> 	instead of _bfd_alloc_and_read.  Don't terminate the string
> 	section again.  Call _bfd_mmap_readonly_temporary and
> 	_bfd_munmap_readonly_temporary instead of _bfd_malloc_and_read
> 	and free.
> 	(_bfd_elf_slurp_version_tables): Call _bfd_mmap_readonly_temporary
> 	and _bfd_munmap_readonly_temporary instead of _bfd_malloc_and_read
> 	and free.
> 	* elflink.c (bfd_elf_link_record_dynamic_symbol): Use bfd_malloc
> 	to get the unversioned symbol.
> 	* libbfd-in.h (_bfd_pagesize): New.
> 	(_bfd_pagesize_m1): Likewise.
> 	(_bfd_minimum_mmap_size): Likewise.
> 	(_bfd_mmap_readonly_persistent): Likewise.
> 	(_bfd_mmap_readonly_temporary): Likewise.
> 	(_bfd_munmap_readonly_temporary): Likewise.
> 	* libbfd.c
> 	(bfd_allocate_mmapped_page): New.
> 	(_bfd_mmap_readonly_temporary): Likewise.
> 	(_bfd_munmap_readonly_temporary): Likewise.
> 	(_bfd_mmap_readonly_persistent): Likewise.
> 	(_bfd_pagesize): Likewise.
> 	(_bfd_pagesize_m1): Likewise.
> 	(_bfd_minimum_mmap_size): Likewise.
> 	(bfd_init_pagesize): Likewise.
> 	* lynx-core.c (lynx_core_file_p): Use _bfd_pagesize.
> 	* opncls.c (_bfd_delete_bfd): Munmap tracked mmapped memories.
> 	* sysdep.h (MAP_ANONYMOUS): New. Define if undefined.
> 	* bfd-in2.h: Regenerated.
> 	* libbfd.h: Likewise.

Hi,

Since this commit, when building for --host=x86_64-w64-mingw32, I get:


make[4]: Entering directory '/home/simark/build/binutils-gdb-x86_64-w64-mingw32/bfd'
  CC       libbfd.lo
/home/simark/src/binutils-gdb/bfd/libbfd.c: In function ‘bfd_init_pagesize’:
/home/simark/src/binutils-gdb/bfd/libbfd.c:1583:19: error: implicit declaration of function ‘getpagesize’ [-Werror=implicit-function-declaration]
 1583 |   _bfd_pagesize = getpagesize ();
      |                   ^~~~~~~~~~~

Simon