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mold/elf/arch-m68k.cc

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// This file contains code for the Motorola 68000 series microprocessors,
// which is often abbreviated as m68k. Running a Unix-like system on a
// m68k-based machine today is probably a retro-computing hobby activity,
// but the processor was a popular choice to build Unix computers during
// '80s. Early Sun workstations for example used m68k. Macintosh until
// 1994 were based on m68k as well until they switched to PowerPC (and
// then to x86 and to ARM.)
//
// From the linker's point of view, it is not hard to support m68k. It's
// just a 32-bit big-endian CISC ISA. Compared to comtemporary i386,
// m68k's psABI is actually simpler because m68k has PC-relative memory
// access instructions and therefore can support position-independent
// code without too much hassle.
//
// https://github.com/rui314/psabi/blob/main/m68k.pdf
#include "mold.h"
namespace mold::elf {
using E = M68K;
template <>
void write_plt_header(Context<E> &ctx, u8 *buf) {
static const u8 insn[] = {
0x2f, 0x00, // move.l %d0, -(%sp)
0x2f, 0x3b, 0x01, 0x70, 0, 0, 0, 0, // move.l (GOTPLT+4, %pc), -(%sp)
0x4e, 0xfb, 0x01, 0x71, 0, 0, 0, 0, // jmp ([GOTPLT+8, %pc])
};
memcpy(buf, insn, sizeof(insn));
*(ub32 *)(buf + 6) = ctx.gotplt->shdr.sh_addr - ctx.plt->shdr.sh_addr;
*(ub32 *)(buf + 14) = ctx.gotplt->shdr.sh_addr - ctx.plt->shdr.sh_addr - 4;
}
template <>
void write_plt_entry(Context<E> &ctx, u8 *buf, Symbol<E> &sym) {
static const u8 insn[] = {
0x20, 0x3c, 0, 0, 0, 0, // move.l PLT_OFFSET, %d0
0x4e, 0xfb, 0x01, 0x71, 0, 0, 0, 0, // jmp ([GOTPLT_ENTRY, %pc])
};
memcpy(buf, insn, sizeof(insn));
*(ub32 *)(buf + 2) = sym.get_plt_idx(ctx) * sizeof(ElfRel<E>);
*(ub32 *)(buf + 10) = sym.get_gotplt_addr(ctx) - sym.get_plt_addr(ctx) - 8;
}
template <>
void write_pltgot_entry(Context<E> &ctx, u8 *buf, Symbol<E> &sym) {
static const u8 insn[] = {
0x4e, 0xfb, 0x01, 0x71, 0, 0, 0, 0, // jmp ([GOT_ENTRY, %pc])
};
memcpy(buf, insn, sizeof(insn));
*(ub32 *)(buf + 4) = sym.get_got_addr(ctx) - sym.get_plt_addr(ctx) - 2;
}
template <>
void EhFrameSection<E>::apply_reloc(Context<E> &ctx, const ElfRel<E> &rel,
u64 offset, u64 val) {
u8 *loc = ctx.buf + this->shdr.sh_offset + offset;
switch (rel.r_type) {
case R_NONE:
break;
case R_68K_32:
*(ub32 *)loc = val;
break;
case R_68K_PC32:
*(ub32 *)loc = val - this->shdr.sh_addr - offset;
break;
default:
Fatal(ctx) << "unsupported relocation in .eh_frame: " << rel;
}
}
template <>
void InputSection<E>::apply_reloc_alloc(Context<E> &ctx, u8 *base) {
std::span<const ElfRel<E>> rels = get_rels(ctx);
ElfRel<E> *dynrel = nullptr;
if (ctx.reldyn)
dynrel = (ElfRel<E> *)(ctx.buf + ctx.reldyn->shdr.sh_offset +
file.reldyn_offset + this->reldyn_offset);
for (i64 i = 0; i < rels.size(); i++) {
const ElfRel<E> &rel = rels[i];
if (rel.r_type == R_NONE)
continue;
Symbol<E> &sym = *file.symbols[rel.r_sym];
u8 *loc = base + rel.r_offset;
auto check = [&](i64 val, i64 lo, i64 hi) {
if (val < lo || hi <= val)
Error(ctx) << *this << ": relocation " << rel << " against "
<< sym << " out of range: " << val << " is not in ["
<< lo << ", " << hi << ")";
};
auto write16 = [&](u64 val) {
check(val, 0, 1 << 16);
*(ub16 *)loc = val;
};
auto write16s = [&](u64 val) {
check(val, -(1 << 15), 1 << 15);
*(ub16 *)loc = val;
};
auto write8 = [&](u64 val) {
check(val, 0, 1 << 8);
*loc = val;
};
auto write8s = [&](u64 val) {
check(val, -(1 << 7), 1 << 7);
*loc = val;
};
u64 S = sym.get_addr(ctx);
u64 A = rel.r_addend;
u64 P = get_addr() + rel.r_offset;
u64 G = sym.get_got_idx(ctx) * sizeof(Word<E>);
u64 GOT = ctx.got->shdr.sh_addr;
switch (rel.r_type) {
case R_68K_32:
apply_dyn_absrel(ctx, sym, rel, loc, S, A, P, dynrel);
break;
case R_68K_16:
write16(S + A);
break;
case R_68K_8:
write8(S + A);
break;
case R_68K_PC32:
case R_68K_PLT32:
*(ub32 *)loc = S + A - P;
break;
case R_68K_PC16:
case R_68K_PLT16:
write16s(S + A - P);
break;
case R_68K_PC8:
case R_68K_PLT8:
write8s(S + A - P);
break;
case R_68K_GOTPCREL32:
*(ub32 *)loc = GOT + A - P;
break;
case R_68K_GOTPCREL16:
write16s(GOT + A - P);
break;
case R_68K_GOTPCREL8:
write8s(GOT + A - P);
break;
case R_68K_GOTOFF32:
*(ub32 *)loc = G + A;
break;
case R_68K_GOTOFF16:
write16(G + A);
break;
case R_68K_GOTOFF8:
write8(G + A);
break;
case R_68K_TLS_GD32:
*(ub32 *)loc = sym.get_tlsgd_addr(ctx) + A - GOT;
break;
case R_68K_TLS_GD16:
write16(sym.get_tlsgd_addr(ctx) + A - GOT);
break;
case R_68K_TLS_GD8:
write8(sym.get_tlsgd_addr(ctx) + A - GOT);
break;
case R_68K_TLS_LDM32:
*(ub32 *)loc = ctx.got->get_tlsld_addr(ctx) + A - GOT;
break;
case R_68K_TLS_LDM16:
write16(ctx.got->get_tlsld_addr(ctx) + A - GOT);
break;
case R_68K_TLS_LDM8:
write8(ctx.got->get_tlsld_addr(ctx) + A - GOT);
break;
case R_68K_TLS_LDO32:
*(ub32 *)loc = S + A - ctx.dtp_addr;
break;
case R_68K_TLS_LDO16:
write16s(S + A - ctx.dtp_addr);
break;
case R_68K_TLS_LDO8:
write8s(S + A - ctx.dtp_addr);
break;
case R_68K_TLS_IE32:
*(ub32 *)loc = sym.get_gottp_addr(ctx) + A - GOT;
break;
case R_68K_TLS_IE16:
write16(sym.get_gottp_addr(ctx) + A - GOT);
break;
case R_68K_TLS_IE8:
write8(sym.get_gottp_addr(ctx) + A - GOT);
break;
case R_68K_TLS_LE32:
*(ub32 *)loc = S + A - ctx.tp_addr;
break;
case R_68K_TLS_LE16:
write16(S + A - ctx.tp_addr);
break;
case R_68K_TLS_LE8:
write8(S + A - ctx.tp_addr);
break;
default:
unreachable();
}
}
}
template <>
void InputSection<E>::apply_reloc_nonalloc(Context<E> &ctx, u8 *base) {
std::span<const ElfRel<E>> rels = get_rels(ctx);
for (i64 i = 0; i < rels.size(); i++) {
const ElfRel<E> &rel = rels[i];
if (rel.r_type == R_NONE || record_undef_error(ctx, rel))
continue;
Symbol<E> &sym = *file.symbols[rel.r_sym];
u8 *loc = base + rel.r_offset;
SectionFragment<E> *frag;
i64 frag_addend;
std::tie(frag, frag_addend) = get_fragment(ctx, rel);
u64 S = frag ? frag->get_addr(ctx) : sym.get_addr(ctx);
u64 A = frag ? frag_addend : (i64)rel.r_addend;
switch (rel.r_type) {
case R_68K_32:
if (std::optional<u64> val = get_tombstone(sym, frag))
*(ub32 *)loc = *val;
else
*(ub32 *)loc = S + A;
break;
default:
Fatal(ctx) << *this << ": invalid relocation for non-allocated sections: "
<< rel;
}
}
}
template <>
void InputSection<E>::scan_relocations(Context<E> &ctx) {
assert(shdr().sh_flags & SHF_ALLOC);
this->reldyn_offset = file.num_dynrel * sizeof(ElfRel<E>);
std::span<const ElfRel<E>> rels = get_rels(ctx);
for (i64 i = 0; i < rels.size(); i++) {
const ElfRel<E> &rel = rels[i];
if (rel.r_type == R_NONE || record_undef_error(ctx, rel))
continue;
Symbol<E> &sym = *file.symbols[rel.r_sym];
if (sym.is_ifunc())
Error(ctx) << sym << ": GNU ifunc symbol is not supported on m68k";
switch (rel.r_type) {
case R_68K_32:
scan_dyn_absrel(ctx, sym, rel);
break;
case R_68K_16:
case R_68K_8:
scan_absrel(ctx, sym, rel);
break;
case R_68K_PC32:
case R_68K_PC16:
case R_68K_PC8:
scan_pcrel(ctx, sym, rel);
break;
case R_68K_GOTPCREL32:
case R_68K_GOTPCREL16:
case R_68K_GOTPCREL8:
case R_68K_GOTOFF32:
case R_68K_GOTOFF16:
case R_68K_GOTOFF8:
sym.flags |= NEEDS_GOT;
break;
case R_68K_PLT32:
case R_68K_PLT16:
case R_68K_PLT8:
if (sym.is_imported)
sym.flags |= NEEDS_PLT;
break;
case R_68K_TLS_GD32:
case R_68K_TLS_GD16:
case R_68K_TLS_GD8:
sym.flags |= NEEDS_TLSGD;
break;
case R_68K_TLS_LDM32:
case R_68K_TLS_LDM16:
case R_68K_TLS_LDM8:
ctx.needs_tlsld = true;
break;
case R_68K_TLS_IE32:
case R_68K_TLS_IE16:
case R_68K_TLS_IE8:
sym.flags |= NEEDS_GOTTP;
break;
case R_68K_TLS_LE32:
case R_68K_TLS_LE16:
case R_68K_TLS_LE8:
check_tlsle(ctx, sym, rel);
break;
case R_68K_TLS_LDO32:
case R_68K_TLS_LDO16:
case R_68K_TLS_LDO8:
break;
default:
Error(ctx) << *this << ": unknown relocation: " << rel;
}
}
}
} // namespace mold::elf
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