[gold][patch] Fix plugin API so gold doesn't try to access a closed file

[Cary Coutant <ccoutant at google dot com>]

The linker plugin API to support LTO currently turns over management
of file descriptors that are claimed by the plugin to the plugin. This
is a problem when the IR files happen to be members of archives, and
it also means that if the plugin decides to keep the files open, we
may run out of available file descriptors before completing the link.

The attached patch reworks the API so that the linker retains the
management of file descriptors. It hands a file descriptor to a plugin
in the claim-file interface, and guarantees that the descriptor will
remain valid until the claim-file callback returns to the linker. If
the plugin needs to access the file again during the all-symbols-read
callback, it can use a new get-input-file API to obtain an open file
descriptor, and a new release-input-file API to release it.

A new testcase covers IR files in archive libraries and all plugin
testcases now exercise the two new APIs.

Since the only changes outside of the plugin code are trivial  (the
changes to descriptors.* and fileread.* are nearly complete reversions
of the original plugin checkin), I'm going to go ahead and commit this
patch.

-cary


include/:

	* plugin-api.h (LDPS_BAD_HANDLE): New constant.
	(ld_plugin_get_input_file): New typedef.
	(ld_plugin_release_input_file): New typedef.
	(LDPT_GET_INPUT_FILE, LDPT_RELEASE_INPUT_FILE): New constants.
	(struct ld_plugin_tv): Add two new fields.

gold/:

	* archive.cc (Archive::get_elf_object_for_member): Remove call
	to File_read::claim_for_plugin.
	* descriptors.cc (Descriptors::open): Remove reference to
	is_claimed.
	(Descriptors::claim_for_plugin): Remove.
	* descriptors.h (Descriptors::claim_for_plugin): Remove.
	(Descriptors::is_claimed): Remove.
	(claim_descriptor_for_plugin): Remove.
	* fileread.cc (File_read::claim_for_plugin): Remove.
	* fileread.h (File_read::claim_for_plugin): Remove.
	(File_read::descriptor): Reopen descriptor if necessary.
	* plugin.cc  (Plugin::load): Add two new APIs to transfer vector.
	(Plugin_manager::all_symbols_read): Add task parameter. Change
	all callers.
	(Plugin_manager::get_input_file): New function.
	(Plugin_manager::release_input_file): New function.
	(Pluginobj::Pluginobj): Add filesize parameter and initialize
	corresponding data member.
	(Sized_pluginobj::Sized_pluginobj): Add filesize parameter
	and pass to base constructor. Change all callers.
	(get_input_file, release_input_file): New functions.
	(make_sized_plugin_object): Add filesize parameter. Change all callers.
	* plugin.h (Plugin_manager::Plugin_manager): Initialize task_ member.
	(Plugin_manager::all_symbols_read): Add task parameter.
	(Plugin_manager::get_input_file): New function.
	(Plugin_manager::release_input_file): New function.
	(Plugin_manager::task_): New data member.
	(Pluginobj::Pluginobj): Add filesize parameter.
	(Pluginobj::filename): New function.
	(Pluginobj::descriptor): New function.
	(Pluginobj::filesize): New function.
	(Pluginobj::filesize_): New data member.
	(Sized_pluginobj::Sized_pluginobj): Add filesize parameter.
	* readsyms.cc (Read_symbols::do_read_symbols): Remove call to
	File_read::claim_for_plugin; use Object::unlock to unlock the file.

	* testsuite/Makefile.am (plugin_test_4): New test case for plugins
	with archive libraries.
	* testsuite/Makefile.in: Regenerate.
	* testsuite/plugin_test.c (struct sym_info): New type.
	(get_input_file, release_input_file): New static variables.
	(onload): Capture new transfer vector entries.
	(claim_file_hook): Stop reading at end of file according to filesize.
	Factor out parsing of readelf output into separate function.
	(all_symbols_read_hook): Exercise get_input_file and release_input_file
	APIs and get the source file name from the symbol table.  Convert
	source file name to corresponding object file name.  Print info
	message when adding new input files.
	(parse_readelf_line): New function.
	* testsuite/plugin_test_1.sh: Add checks for new info messages.
	* testsuite/plugin_test_2.sh: Likewise.
	* testsuite/plugin_test_3.sh: Likewise.
	* testsuite/plugin_test_4.sh: New test case.

Attachment: plugin-close-patch.txt
Description: Text document