elf: Use mmap to map in read-only sections

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.

1 files changed, 29 insertions, 0 deletions

diff --git a/bfd/libbfd-in.h b/bfd/libbfd-in.h
index b8b2ce7..c5a79cf 100644
--- a/bfd/libbfd-in.h
+++ b/bfd/libbfd-in.h
@@ -851,6 +851,10 @@ extern struct bfd_link_info *_bfd_get_link_info (bfd *)
 extern bool _bfd_link_keep_memory (struct bfd_link_info *)
   ATTRIBUTE_HIDDEN;
 
+extern uintptr_t _bfd_pagesize ATTRIBUTE_HIDDEN;
+extern uintptr_t _bfd_pagesize_m1 ATTRIBUTE_HIDDEN;
+extern uintptr_t _bfd_minimum_mmap_size ATTRIBUTE_HIDDEN;
+
 #if GCC_VERSION >= 7000
 #define _bfd_mul_overflow(a, b, res) __builtin_mul_overflow (a, b, res)
 #else
@@ -888,6 +892,19 @@ _bfd_alloc_and_read (bfd *abfd, bfd_size_type asize, bfd_size_type rsize)
   return NULL;
 }
 
+#ifdef USE_MMAP
+extern void *_bfd_mmap_readonly_persistent
+  (bfd *, size_t) ATTRIBUTE_HIDDEN;
+extern void *_bfd_mmap_readonly_temporary
+  (bfd *, size_t, void **, size_t *) ATTRIBUTE_HIDDEN;
+extern void _bfd_munmap_readonly_temporary
+  (void *, size_t) ATTRIBUTE_HIDDEN;
+#else
+#define _bfd_mmap_readonly_persistent(abfd, rsize) \
+  _bfd_alloc_and_read (abfd, rsize, rsize)
+#define _bfd_munmap_readonly_temporary(ptr, rsize) free (ptr)
+#endif
+
 static inline void *
 _bfd_malloc_and_read (bfd *abfd, bfd_size_type asize, bfd_size_type rsize)
 {
@@ -910,3 +927,15 @@ _bfd_malloc_and_read (bfd *abfd, bfd_size_type asize, bfd_size_type rsize)
     }
   return NULL;
 }
+
+#ifndef USE_MMAP
+static inline void *
+_bfd_mmap_readonly_temporary (bfd *abfd, size_t rsize, void **map_addr,
+			      size_t *map_size)
+{
+  void *mem = _bfd_malloc_and_read (abfd, rsize, rsize);
+  *map_addr = mem;
+  *map_size = rsize;
+  return mem;
+}
+#endif