From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Maciej W. Rozycki" To: binutils@sourceware.cygnus.com Subject: R_MIPS_PC16 relocation handling, a proposal Date: Tue, 12 Oct 1999 09:41:00 -0000 Message-id: X-SW-Source: 1999-10/msg00046.html Hi, Guessing from MIPS ISA and ABI documents it seems there is no much use of R_MIPS_PC16 relocations. On the other hand, the b* branch opcode family uses a shifted by two bits 16-bit PC-relative field that is not handled by any of MIPS relocations. I think the authors of ABI might just missed the fact of the shift when documenting R_MIPS_PC16. Anyway, I propose using R_MIPS_PC16 for BFD_RELOC_16_PCREL_S2 relocations which would allow object modules to contain external references from b* opcodes. As R_MIPS_PC16 is pretty unusable at the moment, nothing should break. Otherwise, we might create a BFD-specific extension (just like e.g. R_386_PC8 for i386). Maciej -- + Maciej W. Rozycki, Technical University of Gdansk, Poland + +--------------------------------------------------------------+ + e-mail: macro@ds2.pg.gda.pl, PGP key available + Mon Oct 11 1999 Maciej W. Rozycki * elf32-mips.c (elf_mips_howto_table): Fix rightshift and pcrel_offset for R_MIPS_PC16. (mips_reloc_map): Replace BFD_RELOC_16_PCREL with BFD_RELOC_16_PCREL_S2. (mips_elf_calculate_relocation): Handle R_MIPS_PC16 properly. (mips_elf_perform_relocation): Fix typos in the comment. * elf64-mips.c (mips_elf64_howto_table_rel): Fix rightshift and pcrel_offset for R_MIPS_PC16. (mips_elf64_howto_table_rela): Likewise. (mips_reloc_map): Replace BFD_RELOC_16_PCREL with BFD_RELOC_16_PCREL_S2. diff -u --recursive --new-file binutils.macro/bfd/elf32-mips.c binutils/bfd/elf32-mips.c --- binutils.macro/bfd/elf32-mips.c Mon Oct 4 16:31:22 1999 +++ binutils/bfd/elf32-mips.c Fri Oct 8 13:29:48 1999 @@ -601,7 +601,7 @@ /* 16 bit PC relative reference. */ HOWTO (R_MIPS_PC16, /* type */ - 0, /* rightshift */ + 2, /* rightshift */ 2, /* size (0 = byte, 1 = short, 2 = long) */ 16, /* bitsize */ true, /* pc_relative */ @@ -612,7 +612,7 @@ true, /* partial_inplace */ 0xffff, /* src_mask */ 0xffff, /* dst_mask */ - false), /* pcrel_offset */ + true), /* pcrel_offset */ /* 16 bit call through global offset table. */ HOWTO (R_MIPS_CALL16, /* type */ @@ -1829,7 +1829,7 @@ { BFD_RELOC_MIPS_GPREL, R_MIPS_GPREL16 }, { BFD_RELOC_MIPS_LITERAL, R_MIPS_LITERAL }, { BFD_RELOC_MIPS_GOT16, R_MIPS_GOT16 }, - { BFD_RELOC_16_PCREL, R_MIPS_PC16 }, + { BFD_RELOC_16_PCREL_S2, R_MIPS_PC16 }, { BFD_RELOC_MIPS_CALL16, R_MIPS_CALL16 }, { BFD_RELOC_MIPS_GPREL32, R_MIPS_GPREL32 }, { BFD_RELOC_MIPS_GOT_HI16, R_MIPS_GOT_HI16 }, @@ -6101,7 +6101,8 @@ break; case R_MIPS_PC16: - value = mips_elf_sign_extend (addend, 16) + symbol - p; + value = (bfd_signed_vma) (mips_elf_sign_extend (addend << 2, 18) + + symbol - p) >> 2; overflowed_p = mips_elf_overflow_p (value, 16); break; @@ -6294,9 +6295,9 @@ ((sub1 << 16) | sub2)). When producing a relocateable object file, the calculation is - (((A < 2) | (P & 0xf0000000) + S) >> 2) + (((A << 2) | (P & 0xf0000000) + S) >> 2) When producing a fully linked file, the calculation is - let R = (((A < 2) | (P & 0xf0000000) + S) >> 2) + let R = (((A << 2) | (P & 0xf0000000) + S) >> 2) ((R & 0x1f0000) << 5) | ((R & 0x3e00000) >> 5) | (R & 0xffff) */ if (!info->relocateable) diff -u --recursive --new-file binutils.macro/bfd/elf64-mips.c binutils/bfd/elf64-mips.c --- binutils.macro/bfd/elf64-mips.c Tue Aug 10 13:16:42 1999 +++ binutils/bfd/elf64-mips.c Fri Oct 8 13:55:04 1999 @@ -246,7 +246,7 @@ /* 16 bit PC relative reference. */ HOWTO (R_MIPS_PC16, /* type */ - 0, /* rightshift */ + 2, /* rightshift */ 2, /* size (0 = byte, 1 = short, 2 = long) */ 16, /* bitsize */ true, /* pc_relative */ @@ -257,7 +257,7 @@ true, /* partial_inplace */ 0xffff, /* src_mask */ 0xffff, /* dst_mask */ - false), /* pcrel_offset */ + true), /* pcrel_offset */ /* 16 bit call through global offset table. */ /* FIXME: This is not handled correctly. */ @@ -800,7 +800,7 @@ /* 16 bit PC relative reference. */ HOWTO (R_MIPS_PC16, /* type */ - 0, /* rightshift */ + 2, /* rightshift */ 2, /* size (0 = byte, 1 = short, 2 = long) */ 16, /* bitsize */ true, /* pc_relative */ @@ -811,7 +811,7 @@ true, /* partial_inplace */ 0, /* src_mask */ 0xffff, /* dst_mask */ - false), /* pcrel_offset */ + true), /* pcrel_offset */ /* 16 bit call through global offset table. */ /* FIXME: This is not handled correctly. */ @@ -1372,7 +1372,7 @@ { BFD_RELOC_MIPS_GPREL, R_MIPS_GPREL16 }, { BFD_RELOC_MIPS_LITERAL, R_MIPS_LITERAL }, { BFD_RELOC_MIPS_GOT16, R_MIPS_GOT16 }, - { BFD_RELOC_16_PCREL, R_MIPS_PC16 }, + { BFD_RELOC_16_PCREL_S2, R_MIPS_PC16 }, { BFD_RELOC_MIPS_CALL16, R_MIPS_CALL16 }, { BFD_RELOC_MIPS_GPREL32, R_MIPS_GPREL32 }, { BFD_RELOC_MIPS_GOT_HI16, R_MIPS_GOT_HI16 },