1 Commits

Author	SHA1	Message	Date
Cary Coutant	5d9f66cb84	Fix problems with bss handling in linker scripts. ... PR 16711 noted that gold allocates file space for BSS sections when using a linker script. I've fixed that by rewriting set_section_addresses and set_section_list_addresses to track the file offset separate from the current virtual address, so that BSS sections do not move the file offset. Now, if a series of BSS sections come at the end of a segment, we do not allocate file space; but if a script forces them into the middle of a segment, we will still allocate file space (matching Gnu ld behavior). I've also added a warning when that happens. That exposed another problem where orphan .bss sections were sometimes placed in the middle of a segment. For example, if the script mentions the .got section, but both .data and .bss are orphans, gold would put both .data and .bss in front of .got. I've fixed that by ensuring that orphan BSS sections are always placed after all other allocated sections. It also exposed a problem where the SUBALIGN property is not handled properly. The ld manual clearly states that it should override input section alignment, whether greater or less than the given alignment, but gold would only increase an input section's alignment. Gold would also place the output section based on its original alignment before the SUBALIGN property took effect, leading to a misaligned output section (where the input section was properly aligned in memory, but was not aligned relative to the start of the section), in violation of the ELF/gABI spec. I've fixed that by making sure that the SUBALIGN property overrides the internal alignment of the input sections as well as the external alignment of the output section. This affected the behavior of script_test_2, which was written to expect a misaligned section. The net effect is, I think, improved compatibility with the BFD linker. There are still cases where orphan placement differs, but the differences should be rarer and less important. ALIGN and SUBALIGN behavior is closer, but still not an exact match -- I still found cases where ld would create a misaligned output section, and where gold will properly align it. gold/ PR gold/16711 * output.cc (Output_section::set_final_data_size): Calculate data size based on relative offset rather than file offset. (Output_segment::set_section_addresses): Track file offset separately from address offset. (Output_segment::set_section_list_addresses): Add pfoff parameter. Track file offset separately. Don't move file offset for BSS sections. * output.h (Output_segment::set_section_list_addresses): Add pfoff parameter. * script-sections.cc (Orphan_section_placement): Add PLACE_LAST_ALLOC. (Orphan_section_placement::Orphan_section_placement): Initialize it. (Orphan_section_placement::output_section_init): Track last allocated section. (Orphan_section_placement::find_place): Place BSS after last allocated section. (Output_section_element_input::set_section_addresses): Always override input section alignment when SUBALIGN is specified. (Output_section_definition::set_section_addresses): Override alignment of output section when SUBALIGN is specified. * testsuite/Makefile.am (script_test_15a, script_test_15b) (script_test_15c): New test cases. * testsuite/Makefile.in: Regenerate. * testsuite/script_test_2.cc: Adjust expected layout. * testsuite/script_test_15.c: New source file. * testsuite/script_test_15a.sh: New shell script. * testsuite/script_test_15a.t: New linker script. * testsuite/script_test_15b.sh: New shell script. * testsuite/script_test_15b.t: New linker script. * testsuite/script_test_15c.sh: New shell script. * testsuite/script_test_15c.t: New linker script.	2016-12-11 17:31:25 -08:00