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mold/elf/arch-i386.cc

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#include "mold.h"
namespace mold::elf {
using E = I386;
static void write_plt_header(Context<E> &ctx, u8 *buf) {
if (ctx.arg.pic) {
static const u8 plt0[] = {
0xff, 0xb3, 0, 0, 0, 0, // pushl GOTPLT+4(%ebx)
0xff, 0xa3, 0, 0, 0, 0, // jmp *GOTPLT+8(%ebx)
0x90, 0x90, 0x90, 0x90, // nop
};
memcpy(buf, plt0, sizeof(plt0));
*(u32 *)(buf + 2) = ctx.gotplt->shdr.sh_addr - ctx.got->shdr.sh_addr + 4;
*(u32 *)(buf + 8) = ctx.gotplt->shdr.sh_addr - ctx.got->shdr.sh_addr + 8;
} else {
static const u8 plt0[] = {
0xff, 0x35, 0, 0, 0, 0, // pushl GOTPLT+4
0xff, 0x25, 0, 0, 0, 0, // jmp *GOTPLT+8
0x90, 0x90, 0x90, 0x90, // nop
};
memcpy(buf, plt0, sizeof(plt0));
*(u32 *)(buf + 2) = ctx.gotplt->shdr.sh_addr + 4;
*(u32 *)(buf + 8) = ctx.gotplt->shdr.sh_addr + 8;
}
}
static void write_plt_entry(Context<E> &ctx, u8 *buf, Symbol<E> &sym,
i64 idx) {
u8 *ent = buf + ctx.plt_hdr_size + sym.get_plt_idx(ctx) * ctx.plt_size;
if (ctx.arg.pic) {
static const u8 data[] = {
0xff, 0xa3, 0, 0, 0, 0, // jmp *foo@GOT(%ebx)
0x68, 0, 0, 0, 0, // pushl $reloc_offset
0xe9, 0, 0, 0, 0, // jmp .PLT0@PC
};
memcpy(ent, data, sizeof(data));
*(u32 *)(ent + 2) = sym.get_gotplt_addr(ctx) - ctx.got->shdr.sh_addr;
} else {
static const u8 data[] = {
0xff, 0x25, 0, 0, 0, 0, // jmp *foo@GOT
0x68, 0, 0, 0, 0, // pushl $reloc_offset
0xe9, 0, 0, 0, 0, // jmp .PLT0@PC
};
memcpy(ent, data, sizeof(data));
*(u32 *)(ent + 2) = sym.get_gotplt_addr(ctx);
}
*(u32 *)(ent + 7) = idx * sizeof(ElfRel<E>);
*(u32 *)(ent + 12) = ctx.plt->shdr.sh_addr - sym.get_plt_addr(ctx) - 16;
}
template <>
void PltSection<E>::copy_buf(Context<E> &ctx) {
u8 *buf = ctx.buf + this->shdr.sh_offset;
write_plt_header(ctx, buf);
for (i64 i = 0; i < symbols.size(); i++)
write_plt_entry(ctx, buf, *symbols[i], i);
}
template <>
void PltGotSection<E>::copy_buf(Context<E> &ctx) {
u8 *buf = ctx.buf + this->shdr.sh_offset;
if (ctx.arg.pic) {
static const u8 data[] = {
0xff, 0xa3, 0, 0, 0, 0, // jmp *foo@GOT(%ebx)
0x66, 0x90, // nop
};
for (i64 i = 0; i < symbols.size(); i++) {
u8 *ent = buf + i * sizeof(data);
memcpy(ent, data, sizeof(data));
*(u32 *)(ent + 2) = symbols[i]->get_got_addr(ctx) - ctx.got->shdr.sh_addr;
}
} else {
static const u8 data[] = {
0xff, 0x25, 0, 0, 0, 0, // jmp *foo@GOT
0x66, 0x90, // nop
};
for (i64 i = 0; i < symbols.size(); i++) {
u8 *ent = buf + i * sizeof(data);
memcpy(ent, data, sizeof(data));
*(u32 *)(ent + 2) = symbols[i]->get_got_addr(ctx);
}
}
}
template <>
void EhFrameSection<E>::apply_reloc(Context<E> &ctx, ElfRel<E> &rel,
u64 offset, u64 val) {
u8 *loc = ctx.buf + this->shdr.sh_offset + offset;
switch (rel.r_type) {
case R_386_NONE:
return;
case R_386_32:
*(u32 *)loc = val;
return;
case R_386_PC32:
*(u32 *)loc = val - this->shdr.sh_addr - offset;
return;
}
unreachable();
}
template <>
void InputSection<E>::apply_reloc_alloc(Context<E> &ctx, u8 *base) {
ElfRel<E> *dynrel = nullptr;
std::span<ElfRel<E>> rels = get_rels(ctx);
i64 frag_idx = 0;
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_386_NONE)
continue;
Symbol<E> &sym = *file.symbols[rel.r_sym];
u8 *loc = base + rel.r_offset;
const SectionFragmentRef<E> *frag_ref = nullptr;
if (rel_fragments && rel_fragments[frag_idx].idx == i)
frag_ref = &rel_fragments[frag_idx++];
auto overflow_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 write8 = [&](u64 val) {
overflow_check(val, 0, 1 << 8);
*loc = val;
};
auto write8s = [&](u64 val) {
overflow_check(val, -(1 << 7), 1 << 7);
*loc = val;
};
auto write16 = [&](u64 val) {
overflow_check(val, 0, 1 << 16);
*(u16 *)loc = val;
};
auto write16s = [&](u64 val) {
overflow_check(val, -(1 << 15), 1 << 15);
*(u16 *)loc = val;
};
auto write32 = [&](u64 val) {
*(u32 *)loc = val;
};
#define S (frag_ref ? frag_ref->frag->get_addr(ctx) : sym.get_addr(ctx))
#define A (frag_ref ? frag_ref->addend : this->get_addend(rel))
#define P (output_section->shdr.sh_addr + offset + rel.r_offset)
#define G (sym.get_got_addr(ctx) - ctx.got->shdr.sh_addr)
#define GOT ctx.got->shdr.sh_addr
switch (rel.r_type) {
case R_386_8:
write8(S + A);
continue;
case R_386_16:
write16(S + A);
continue;
case R_386_32:
if (sym.is_absolute() || !ctx.arg.pic) {
write32(S + A);
} else if (sym.is_imported) {
*dynrel++ = {P, R_386_32, (u32)sym.get_dynsym_idx(ctx)};
write32(A);
} else {
if (!is_relr_reloc(ctx, rel))
*dynrel++ = {P, R_386_RELATIVE, 0};
write32(S + A);
}
continue;
case R_386_PC8:
write8s(S + A);
continue;
case R_386_PC16:
write16s(S + A);
continue;
case R_386_PC32:
if (sym.is_absolute() || !sym.is_imported || !ctx.arg.shared) {
write32(S + A - P);
} else {
*dynrel++ = {P, R_386_32, (u32)sym.get_dynsym_idx(ctx)};
write32(A);
}
continue;
case R_386_PLT32:
write32(S + A - P);
continue;
case R_386_GOT32:
case R_386_GOT32X:
write32(G + A);
continue;
case R_386_GOTOFF:
write32(S + A - GOT);
continue;
case R_386_GOTPC:
write32(GOT + A - P);
continue;
case R_386_TLS_GOTIE:
write32(sym.get_gottp_addr(ctx) + A - GOT);
continue;
case R_386_TLS_LE:
write32(S + A - ctx.tls_end);
continue;
case R_386_TLS_IE:
write32(sym.get_gottp_addr(ctx) + A);
continue;
case R_386_TLS_GD:
if (sym.get_tlsgd_idx(ctx) == -1) {
// Relax GD to LE
switch (rels[i + 1].r_type) {
case R_386_PLT32: {
static const u8 insn[] = {
0x65, 0xa1, 0, 0, 0, 0, // mov %gs:0, %rax
0x81, 0xe8, 0, 0, 0, 0, // add $0, %rax
};
memcpy(loc - 3, insn, sizeof(insn));
*(u32 *)(loc + 5) = ctx.tls_end - S - A;
break;
}
case R_386_GOT32: {
static const u8 insn[] = {
0x65, 0xa1, 0, 0, 0, 0, // mov %gs:0, %rax
0x81, 0xe8, 0, 0, 0, 0, // add $0, %rax
};
memcpy(loc - 2, insn, sizeof(insn));
*(u32 *)(loc + 6) = ctx.tls_end - S - A;
break;
}
default:
unreachable();
}
i++;
} else {
write32(sym.get_tlsgd_addr(ctx) + A - GOT);
}
continue;
case R_386_TLS_LDM:
if (ctx.got->tlsld_idx == -1) {
// Relax LD to LE
switch (rels[i + 1].r_type) {
case R_386_PLT32: {
static const u8 insn[] = {
0x65, 0xa1, 0, 0, 0, 0, // mov %gs:0, %eax
0x8d, 0x74, 0x26, 0x00, // lea (%esi,1), %esi
0x90, // nop
};
memcpy(loc - 2, insn, sizeof(insn));
break;
}
case R_386_GOT32: {
static const u8 insn[] = {
0x65, 0xa1, 0, 0, 0, 0, // mov %gs:0, %eax
0x8d, 0x74, 0x26, 0x00, // lea (%esi,1), %esi
0x66, 0x90,
};
memcpy(loc - 2, insn, sizeof(insn));
break;
}
default:
unreachable();
}
i++;
} else {
write32(ctx.got->get_tlsld_addr(ctx) + A - GOT);
}
continue;
case R_386_TLS_LDO_32:
if (ctx.got->tlsld_idx == -1)
write32(S + A - ctx.tls_end);
else
write32(S + A - ctx.tls_begin);
continue;
case R_386_SIZE32:
write32(sym.esym().st_size + A);
continue;
case R_386_TLS_GOTDESC:
if (sym.get_tlsdesc_idx(ctx) == -1) {
static const u8 insn[] = {
0x8d, 0x05, 0, 0, 0, 0, // lea 0, %eax
};
memcpy(loc - 2, insn, sizeof(insn));
write32(S + A - ctx.tls_end);
} else {
write32(sym.get_tlsdesc_addr(ctx) + A - GOT);
}
continue;
case R_386_TLS_DESC_CALL:
if (ctx.arg.relax && !ctx.arg.shared) {
// call *(%rax) -> nop
loc[0] = 0x66;
loc[1] = 0x90;
}
continue;
default:
unreachable();
}
#undef S
#undef A
#undef P
#undef G
#undef GOT
}
}
template <>
void InputSection<E>::apply_reloc_nonalloc(Context<E> &ctx, u8 *base) {
std::span<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_386_NONE)
continue;
Symbol<E> &sym = *file.symbols[rel.r_sym];
u8 *loc = base + rel.r_offset;
if (!sym.file) {
report_undef(ctx, file, sym);
continue;
}
SectionFragment<E> *frag;
i64 addend;
std::tie(frag, addend) = get_fragment(ctx, rel);
auto overflow_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 write8 = [&](u64 val) {
overflow_check(val, 0, 1 << 8);
*loc = val;
};
auto write8s = [&](u64 val) {
overflow_check(val, -(1 << 7), 1 << 7);
*loc = val;
};
auto write16 = [&](u64 val) {
overflow_check(val, 0, 1 << 16);
*(u16 *)loc = val;
};
auto write16s = [&](u64 val) {
overflow_check(val, -(1 << 15), 1 << 15);
*(u16 *)loc = val;
};
#define S (frag ? frag->get_addr(ctx) : sym.get_addr(ctx))
#define A (frag ? addend : this->get_addend(rel))
#define G (sym.get_got_addr(ctx) - ctx.got->shdr.sh_addr)
#define GOT ctx.got->shdr.sh_addr
switch (rel.r_type) {
case R_386_8:
write8(S + A);
continue;
case R_386_16:
write16(S + A);
continue;
case R_386_32:
if (std::optional<u64> val = get_tombstone(sym))
*(u32 *)loc = *val;
else
*(u32 *)loc = S + A;
continue;
case R_386_PC8:
write8s(S + A);
continue;
case R_386_PC16:
write16s(S + A);
continue;
case R_386_PC32:
*(u32 *)loc = S + A;
continue;
case R_386_GOTPC:
*(u32 *)loc = GOT + A;
continue;
case R_386_GOTOFF:
*(u32 *)loc = S + A - GOT;
continue;
case R_386_TLS_LDO_32:
if (std::optional<u64> val = get_tombstone(sym))
*(u32 *)loc = *val;
else
*(u32 *)loc = S + A - ctx.tls_begin;
continue;
case R_386_SIZE32:
*(u32 *)loc = sym.esym().st_size + A;
continue;
default:
unreachable();
}
#undef S
#undef A
#undef GOT
}
}
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<ElfRel<E>> rels = get_rels(ctx);
// Scan relocations
for (i64 i = 0; i < rels.size(); i++) {
const ElfRel<E> &rel = rels[i];
if (rel.r_type == R_386_NONE)
continue;
Symbol<E> &sym = *file.symbols[rel.r_sym];
if (!sym.file) {
report_undef(ctx, file, sym);
continue;
}
if (sym.get_type() == STT_GNU_IFUNC) {
sym.flags |= NEEDS_GOT;
sym.flags |= NEEDS_PLT;
}
switch (rel.r_type) {
case R_386_8:
case R_386_16: {
Action table[][4] = {
// Absolute Local Imported data Imported code
{ NONE, ERROR, ERROR, ERROR }, // DSO
{ NONE, ERROR, ERROR, ERROR }, // PIE
{ NONE, NONE, COPYREL, CPLT }, // PDE
};
dispatch(ctx, table, i, rel, sym);
break;
}
case R_386_32: {
Action table[][4] = {
// Absolute Local Imported data Imported code
{ NONE, BASEREL, DYNREL, DYNREL }, // DSO
{ NONE, BASEREL, DYNREL, DYNREL }, // PIE
{ NONE, NONE, COPYREL, CPLT }, // PDE
};
dispatch(ctx, table, i, rel, sym);
break;
}
case R_386_PC8:
case R_386_PC16: {
Action table[][4] = {
// Absolute Local Imported data Imported code
{ ERROR, NONE, ERROR, ERROR }, // DSO
{ ERROR, NONE, COPYREL, PLT }, // PIE
{ NONE, NONE, COPYREL, PLT }, // PDE
};
dispatch(ctx, table, i, rel, sym);
break;
}
case R_386_PC32: {
Action table[][4] = {
// Absolute Local Imported data Imported code
{ ERROR, NONE, DYNREL, DYNREL }, // DSO
{ ERROR, NONE, COPYREL, PLT }, // PIE
{ NONE, NONE, COPYREL, PLT }, // PDE
};
dispatch(ctx, table, i, rel, sym);
break;
}
case R_386_GOT32:
case R_386_GOT32X:
case R_386_GOTPC:
sym.flags |= NEEDS_GOT;
break;
case R_386_PLT32: {
Action table[][4] = {
// Absolute Local Imported data Imported code
{ NONE, NONE, PLT, PLT }, // DSO
{ NONE, NONE, PLT, PLT }, // PIE
{ NONE, NONE, PLT, PLT }, // PDE
};
dispatch(ctx, table, i, rel, sym);
break;
}
case R_386_TLS_GOTIE:
case R_386_TLS_LE:
case R_386_TLS_IE:
sym.flags |= NEEDS_GOTTP;
break;
case R_386_TLS_GD:
if (i + 1 == rels.size())
Fatal(ctx) << *this << ": TLS_GD reloc must be followed by PLT or GOT32";
if (u32 ty = rels[i + 1].r_type;
ty != R_386_PLT32 && ty != R_386_GOT32)
Fatal(ctx) << *this << ": TLS_GD reloc must be followed by PLT or GOT32";
if (ctx.arg.relax && !ctx.arg.shared && !sym.is_imported)
i++;
else
sym.flags |= NEEDS_TLSGD;
break;
case R_386_TLS_LDM:
if (i + 1 == rels.size())
Fatal(ctx) << *this << ": TLS_LDM reloc must be followed by PLT or GOT32";
if (u32 ty = rels[i + 1].r_type;
ty != R_386_PLT32 && ty != R_386_GOT32)
Fatal(ctx) << *this << ": TLS_LDM reloc must be followed by PLT or GOT32";
if (ctx.arg.relax && !ctx.arg.shared)
i++;
else
ctx.needs_tlsld = true;
break;
case R_386_TLS_GOTDESC:
if (!ctx.arg.relax || ctx.arg.shared)
sym.flags |= NEEDS_TLSDESC;
break;
case R_386_GOTOFF:
case R_386_TLS_LDO_32:
case R_386_SIZE32:
case R_386_TLS_DESC_CALL:
break;
default:
Error(ctx) << *this << ": unknown relocation: " << rel;
}
}
}
} // namespace mold::elf
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