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Refactor X86_64TargetInfo::relaxTlsIeToLe. 

This patch is to rewrite the function with a table-lookup-ish approach
so that it can read as a series of "convert this pattern to this" pattern.

llvm-svn: 273238
This commit is contained in:
Rui Ueyama 2016-06-21 03:42:32 +00:00
parent 68bf7d8c2a
commit 55a9def2bf
2 changed files with 35 additions and 31 deletions
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58
lld/ELF/Target.cpp
View File

@ -677,34 +677,40 @@ void X86_64TargetInfo::relaxTlsGdToIe(uint8_t *Loc, uint32_t Type,
// R_X86_64_TPOFF32 so that it does not use GOT.
void X86_64TargetInfo::relaxTlsIeToLe(uint8_t *Loc, uint32_t Type,
uint64_t Val) const {
// Ulrich's document section 6.5 says that @gottpoff(%rip) must be
// used in MOVQ or ADDQ instructions only.
// "MOVQ foo@GOTTPOFF(%RIP), %REG" is transformed to "MOVQ $foo, %REG".
// "ADDQ foo@GOTTPOFF(%RIP), %REG" is transformed to "LEAQ foo(%REG), %REG"
// (if the register is not RSP/R12) or "ADDQ $foo, %RSP".
// Opcodes info can be found at http://ref.x86asm.net/coder64.html#x48.
uint8_t *Prefix = Loc - 3;
uint8_t *Inst = Loc - 2;
uint8_t *RegSlot = Loc - 1;
uint8_t *Inst = Loc - 3;
uint8_t Reg = Loc[-1] >> 3;
bool IsMov = *Inst == 0x8b;
bool RspAdd = !IsMov && Reg == 4;
uint8_t RegSlot = Loc - 1;
// r12 and rsp registers requires special handling.
// Problem is that for other registers, for example leaq 0xXXXXXXXX(%r11),%r11
// result out is 7 bytes: 4d 8d 9b XX XX XX XX,
// but leaq 0xXXXXXXXX(%r12),%r12 is 8 bytes: 4d 8d a4 24 XX XX XX XX.
// The same true for rsp. So we convert to addq for them, saving 1 byte that
// we dont have.
if (RspAdd)
*Inst = 0x81;
else
*Inst = IsMov ? 0xc7 : 0x8d;
if (*Prefix == 0x4c)
*Prefix = (IsMov || RspAdd) ? 0x49 : 0x4d;
*RegSlot = (IsMov || RspAdd) ? (0xc0 | Reg) : (0x80 | Reg | (Reg << 3));
// The original code used a pc relative relocation and so we have to
// compensate for the -4 in had in the addend.
// Note that LEA with RSP or R12 is converted to ADD instead of LEA
// because LEA with these registers needs 4 bytes to encode and thus
// wouldn't fit the space.
if (memcmp(Inst, "\x48\x03\x25", 3) == 0) {
// "addq foo@gottpoff(%rip),%rsp" -> "addq $foo,%rsp"
memcpy(Inst, "\x48\x81\xc4", 3);
} else if (memcmp(Inst, "\x4c\x03\x25", 3) == 0) {
// "addq foo@gottpoff(%rip),%r12" -> "addq $foo,%r12"
memcpy(Inst, "\x49\x81\xc4", 3);
} else if (memcmp(Inst, "\x4c\x03", 2) == 0) {
// "addq foo@gottpoff(%rip),%r[8-15]" -> "leaq foo(%r[8-15]),%r[8-15]"
memcpy(Inst, "\x4d\x8d", 2);
*RegSlot = 0x80 | (Reg << 3) | Reg;
} else if (memcmp(Inst, "\x48\x03", 2) == 0) {
// "addq foo@gottpoff(%rip),%reg -> "leaq foo(%reg),%reg"
memcpy(Inst, "\x48\x8d", 2);
*RegSlot = 0x80 | (Reg << 3) | Reg;
} else if (memcmp(Inst, "\x4c\x8b", 2) == 0) {
// "movq foo@gottpoff(%rip),%r[8-15]" -> "movq $foo,%r[8-15]"
memcpy(Inst, "\x49\xc7", 2);
*RegSlot = 0xc0 | Reg;
} else if (memcmp(Inst, "\x48\x8b", 2) == 0) {
// "movq foo@gottpoff(%rip),%reg" -> "movq $foo,%reg"
memcpy(Inst, "\x48\xc7", 2);
*RegSlot = 0xc0 | Reg;
}
// The original code used a PC relative relocation.
// Need to compensate for the -4 it had in the addend.
relocateOne(Loc, R_X86_64_TPOFF32, Val + 4);
}

8
lld/test/ELF/tls-opt.s
View File

@ -20,11 +20,9 @@
// DISASM-NEXT: 1103f: 4d 8d bf fc ff ff ff leaq -4(%r15), %r15
// DISASM-NEXT: 11046: 48 81 c4 fc ff ff ff addq $-4, %rsp
// DISASM-NEXT: 1104d: 49 81 c4 fc ff ff ff addq $-4, %r12
// Corrupred output:
// DISASM-NEXT: 11054: 48 8d 80 f8 ff ff ff leaq -8(%rax), %rax
// DISASM-NEXT: 1105b: 48 d1 81 c4 fc ff ff rolq -828(%rcx)
// DISASM-NEXT: 11062: ff 48 d1 decl -47(%rax)
// DISASM-NEXT: 11065: 81 c4 fc ff ff ff addl $4294967292, %esp
// DISASM-NEXT: 11054: 48 87 05 f8 ff ff ff xchgq %rax, -8(%rip)
// DISASM-NEXT: 1105b: 48 d1 24 25 fc ff ff ff shlq -4
// DISASM-NEXT: 11063: 48 d1 04 25 fc ff ff ff rolq -4
// LD to LE:
// DISASM-NEXT: 1106b: 66 66 66 64 48 8b 04 25 00 00 00 00 movq %fs:0, %rax
// DISASM-NEXT: 11077: 48 8d 88 f8 ff ff ff leaq -8(%rax), %rcx