ELF: Synthesize R_RISCV_ALIGN at input section start #5
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Without linker relaxation enabled for a particular relocatable file or section (e.g., using .option norelax), the assembler will not generate R_RISCV_ALIGN relocations for alignment directives. This becomes problematic in a two-stage linking process: ``` ld -r a.o b.o -o ab.o // b.o is norelax. Its alignment information is lost in ab.o. ld ab.o -o ab ``` When ab.o is linked into an executable, the preceding relaxed section (a.o's content) might shrink. Since there's no R_RISCV_ALIGN relocation in b.o for the linker to act upon, the `.word 0x3a393837` data in b.o may end up unaligned in the final executable. To address the issue, this patch inserts NOP bytes and synthesizes an R_RISCV_ALIGN relocation at the beginning of a text section when the alignment >= 4. For simplicity, when RVC is disabled, we synthesize an ALIGN relocation (addend: 2) for a 4-byte aligned section, allowing the linker to trim the excess 2 bytes. See also https://sourceware.org/bugzilla/show_bug.cgi?id=33236
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See also https://sourceware.org/bugzilla/show_bug.cgi?id=33236