Linker: Strict relocation handling #136
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After ratification of the RISC-V psABI specification (version 1.0), it is getting enhanced and improved. This commit performs following changes. 1. Reject unknown ELF relocation types when fed into a tool Before this commit, it accepted unknown (but small) relocation types and relocation types only for internal uses (linker relaxation). More worryingly, some internal only relocation types conflict with global relocation types in the latest psABI draft [1]. [1] <riscv-non-isa/riscv-elf-psabi-doc@d49e480> If (a) psABI changes conflict with internal only relocation types and/or (b) an object (possibly malicious or just from the future) with unknown relocation type is encountered while linking (by ld) or relocating by other tools, it can cause a severe failure (with unpredictable erroneous results). This commit now rejects small unknown relocation types and internal only ones when an ELF file with such relocation types is fed into a tool. 2. Move internal only ELF relocation types after all regular ones Currently, we have six internal only relocation types but only R_RISCV_DELETE is distinguished from the regular one (others were defined in between regular relocation types). This design caused the conflict with regular relocation types *and* made fixing the number of such internal relocation a non-trivial task. This commit moves all internal only relocation types (not only R_RISCV_DELETE) after R_RISCV_max and creates separate howto relocation table for range (R_RISCV_DELETE + 1..R_RISCV_internal_max). All internal only relocations are defined relative to R_RISCV_max and will not conflict with regular ones (if psABI started to use large numbers, internal relocations are automatically adjusted). 3. Prevent internal only ELF relocation types from emitting It prevents emitting internal only relocations when the --emit-relocs option is specified when linking (instead, replaces such internal only relocations to R_RISCV_NONE). bfd/ChangeLog: * elfnn-riscv.c (R_RISCV_DELETE): Move to elf_riscv_reloc_type. (riscv_info_to_howto_rela, bad_static_reloc): Reflect riscv_elf_rtype_to_howto changes. (riscv_elf_check_relocs): Likewise. Also reject unknown relocs are found. Reuse howto variable. (riscv_elf_relocate_section): Reflect riscv_elf_rtype_to_howto changesL but also look up for internal relocs only when necessary. Delete internal only relocation after the relocation. * elfxx-riscv.c (HOWTO_ISEMPTY): New macro to query whether the howto entry is empty. (howto_table): Reserve all howto entries defined by the latest RISC-V psABI specification except no actual EMPTY_HOWTO defs at the end of the list. Move internal only relocs to... (howto_table_internal): ...here. (riscv_elf_rtype_to_howto): Add ability to look up internal only relocation types only when necessary. * elfxx-riscv.h (riscv_elf_rtype_to_howto): Reflect above. include/ChangeLog: * elf/riscv.h (enum elf_riscv_reloc_type): Comment all reserved relocation types as defined by the latest RISC-V psABI spec. Move all internal relocation types after R_RISCV_max, first being R_RISCV_DELETE. Add R_RISCV_internal_max. Add safety guard for all relocation types on C11 and later.
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Wiki Page (details): https://github.com/a4lg/binutils-gdb/wiki/riscv_linker_reloc_strict_1