Re: [gold patch] Incremental 15/18: Add --incremental-base option.

[Ian Lance Taylor <iant@google.com>]

Cary Coutant <ccoutant@google.com> writes:

> 	* gold.cc (queue_initial_tasks): Pass incremental base filename
> 	to Output_file::open_base_file; don't print error message.
> 	* incremental-dump.cc (main): Adjust call to
> 	Output_file::open_for_modification.
> 	* incremental-dump.cc (main): Likewise.
> 	* incremental.cc (Incremental_inputs::report_command_line):
> 	Ignore --incremental-base option when comparing command lines.
> 	* options.h (class General_options): Add --incremental-base.
> 	* output.cc (Output_file::Output_file):
> 	(Output_file::open_base_file): Add base_name and writable parameters;
> 	copy base file to new file; print error message here.
> 	(Output_file::map_no_anonymous): Add writable parameter; adjust all
> 	callers.
> 	* output.h (Output_file::open_for_modification): Rename to...
> 	(Output_file::open_base_file): ...this; add base_name and
> 	writable parameters; adjust all callers.
> 	(Output_file::map_no_anonymous): Add writable parameter; adjust all
> 	callers.
> 	* testsuite/Makefile.am (incremental_test_4): Test
> 	--incremental-base.
> 	* testsuite/Makefile.in: Regenerate.


> @@ -861,6 +861,7 @@ Incremental_inputs::report_command_line(int argc, const char* const* argv)
>  	  || strcmp(argv[i], "--incremental-changed") == 0
>  	  || strcmp(argv[i], "--incremental-unchanged") == 0
>  	  || strcmp(argv[i], "--incremental-unknown") == 0
> +	  || is_prefix_of("--incremental-base=", argv[i])
>  	  || is_prefix_of("--debug=", argv[i]))
>          continue;

Will this work correctly if the user does
    ld --incremental-base old-file
?  That is, if they pass the argument as a separate argv entry, rather
than using =?  I guess the same question arises for --debug.


> +  // If the base file and the output file are different, open a
> +  // new output file and copy the contents from the base file.
> +  if (use_base_file)
> +    {
> +      unsigned char* base = this->base_;
> +      this->open(s.st_size);
> +      memcpy(this->base_, base, s.st_size);
> +      ::munmap(base, s.st_size);
> +      ::close(o);
> +    }

You're going to some mild contortions to map in the base file, and then
you are throwing away the mapping.  If you are going to stick with this
copying approach, then I think it would be simpler to just map the
output file as for a non-incremental link, and then open() the base file
and read() the contents into the mapping you just created.  That will be
just as efficient--it's a nice sequential read--and will save you from
running out of memory when you in effect map the output file twice.

Ian