forked from OSchip/llvm-project
[ELF] - Implement the TLS relocation optimization for 32-bit x86.
Implement the TLS relocation optimization for 32-bit x86 that is described in "ELF Handling For Thread-Local Storage" by Ulrich Drepper, chapter 5, "IA-32 Linker Optimizations". Specifically, this patch implements these optimizations: LD->LE, GD->IE, GD->LD, and IE->LE. Differential revision: http://reviews.llvm.org/D15292 llvm-svn: 255103
This commit is contained in:
George Rimar
parent
9938425b31
commit
2558e12bac
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@ -88,6 +88,20 @@ public:
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bool relocNeedsPlt(uint32_t Type, const SymbolBody &S) const override;
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void relocateOne(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type, uint64_t P,
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uint64_t SA, uint8_t *PairedLoc = nullptr) const override;
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bool isTlsOptimized(unsigned Type, const SymbolBody *S) const override;
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unsigned relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type,
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uint64_t P, uint64_t SA,
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const SymbolBody &S) const override;
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private:
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void relocateTlsLdToLe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
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uint64_t SA) const;
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void relocateTlsGdToIe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
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uint64_t SA) const;
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void relocateTlsGdToLe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
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uint64_t SA) const;
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void relocateTlsIeToLe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
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uint64_t SA) const;
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};
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class X86_64TargetInfo final : public TargetInfo {
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@ -260,7 +274,7 @@ bool X86TargetInfo::isTlsDynReloc(unsigned Type) const {
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if (Type == R_386_TLS_LE || Type == R_386_TLS_LE_32 ||
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Type == R_386_TLS_GOTIE)
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return Config->Shared;
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return false;
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return Type == R_386_TLS_GD;
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}
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void X86TargetInfo::writePltZeroEntry(uint8_t *Buf, uint64_t GotEntryAddr,
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@ -311,8 +325,11 @@ bool X86TargetInfo::relocNeedsCopy(uint32_t Type, const SymbolBody &S) const {
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}
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bool X86TargetInfo::relocNeedsGot(uint32_t Type, const SymbolBody &S) const {
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return Type == R_386_TLS_GOTIE || Type == R_386_GOT32 ||
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relocNeedsPlt(Type, S);
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if (S.isTLS() && Type == R_386_TLS_GD)
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return Target->isTlsOptimized(Type, &S) && canBePreempted(&S, true);
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if (Type == R_386_TLS_GOTIE)
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return !isTlsOptimized(Type, &S);
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return Type == R_386_GOT32 || relocNeedsPlt(Type, S);
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}
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bool X86TargetInfo::relocNeedsPlt(uint32_t Type, const SymbolBody &S) const {
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@ -358,6 +375,121 @@ void X86TargetInfo::relocateOne(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type,
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}
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}
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bool X86TargetInfo::isTlsOptimized(unsigned Type, const SymbolBody *S) const {
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if (Config->Shared || (S && !S->isTLS()))
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return false;
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return Type == R_386_TLS_LDO_32 || Type == R_386_TLS_LDM ||
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Type == R_386_TLS_GD ||
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(Type == R_386_TLS_GOTIE && !canBePreempted(S, true));
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}
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unsigned X86TargetInfo::relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd,
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uint32_t Type, uint64_t P,
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uint64_t SA,
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const SymbolBody &S) const {
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switch (Type) {
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case R_386_TLS_GD:
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if (canBePreempted(&S, true))
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relocateTlsGdToIe(Loc, BufEnd, P, SA);
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else
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relocateTlsGdToLe(Loc, BufEnd, P, SA);
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// The next relocation should be against __tls_get_addr, so skip it
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return 1;
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case R_386_TLS_GOTIE:
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relocateTlsIeToLe(Loc, BufEnd, P, SA);
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return 0;
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case R_386_TLS_LDM:
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relocateTlsLdToLe(Loc, BufEnd, P, SA);
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// The next relocation should be against __tls_get_addr, so skip it
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return 1;
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case R_386_TLS_LDO_32:
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relocateOne(Loc, BufEnd, R_386_TLS_LE, P, SA);
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return 0;
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}
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llvm_unreachable("Unknown TLS optimization");
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}
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// "Ulrich Drepper, ELF Handling For Thread-Local Storage" (5.1
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// IA-32 Linker Optimizations, http://www.akkadia.org/drepper/tls.pdf) shows
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// how GD can be optimized to IE:
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// leal x@tlsgd(, %ebx, 1),
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// call __tls_get_addr@plt
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// Is converted to:
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// movl %gs:0, %eax
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// addl x@gotntpoff(%ebx), %eax
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void X86TargetInfo::relocateTlsGdToIe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
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uint64_t SA) const {
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const uint8_t Inst[] = {
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0x65, 0xa1, 0x00, 0x00, 0x00, 0x00, // movl %gs:0, %eax
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0x03, 0x83, 0x00, 0x00, 0x00, 0x00 // addl 0(%ebx), %eax
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};
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memcpy(Loc - 3, Inst, sizeof(Inst));
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relocateOne(Loc + 5, BufEnd, R_386_32, P,
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SA - Out<ELF32LE>::Got->getVA() -
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Out<ELF32LE>::Got->getNumEntries() * 4);
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}
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// GD can be optimized to LE:
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// leal x@tlsgd(, %ebx, 1),
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// call __tls_get_addr@plt
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// Can be converted to:
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// movl %gs:0,%eax
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// addl $x@ntpoff,%eax
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// But gold emits subl $foo@tpoff,%eax instead of addl.
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// These instructions are completely equal in behavior.
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// This method generates subl to be consistent with gold.
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void X86TargetInfo::relocateTlsGdToLe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
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uint64_t SA) const {
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const uint8_t Inst[] = {
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0x65, 0xa1, 0x00, 0x00, 0x00, 0x00, // movl %gs:0, %eax
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0x81, 0xe8, 0x00, 0x00, 0x00, 0x00 // subl 0(%ebx), %eax
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};
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memcpy(Loc - 3, Inst, sizeof(Inst));
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relocateOne(Loc + 5, BufEnd, R_386_32, P,
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Out<ELF32LE>::TlsPhdr->p_memsz - SA);
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}
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// LD can be optimized to LE:
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// leal foo(%reg),%eax
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// call ___tls_get_addr
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// Is converted to:
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// movl %gs:0,%eax
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// nop
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// leal 0(%esi,1),%esi
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void X86TargetInfo::relocateTlsLdToLe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
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uint64_t SA) const {
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const uint8_t Inst[] = {
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0x65, 0xa1, 0x00, 0x00, 0x00, 0x00, // movl %gs:0,%eax
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0x90, // nop
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0x8d, 0x74, 0x26, 0x00 // leal 0(%esi,1),%esi
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};
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memcpy(Loc - 2, Inst, sizeof(Inst));
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}
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// In some conditions, R_386_TLS_GOTIE relocation can be optimized to
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// R_386_TLS_LE so that it does not use GOT.
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// This function does that. Read "ELF Handling For Thread-Local Storage,
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// 5.1 IA-32 Linker Optimizations" (http://www.akkadia.org/drepper/tls.pdf)
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// by Ulrich Drepper for details.
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void X86TargetInfo::relocateTlsIeToLe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
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uint64_t SA) const {
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// Ulrich's document section 6.2 says that @gotntpoff can be
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// used with MOVL or ADDL instructions.
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// "MOVL foo@GOTTPOFF(%RIP), %REG" is transformed to "MOVL $foo, %REG".
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// "ADDL foo@GOTNTPOFF(%RIP), %REG" is transformed to "LEAL foo(%REG), %REG"
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// Note: gold converts to ADDL instead of LEAL.
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uint8_t *Inst = Loc - 2;
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uint8_t *RegSlot = Loc - 1;
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uint8_t Reg = (Loc[-1] >> 3) & 7;
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bool IsMov = *Inst == 0x8b;
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*Inst = IsMov ? 0xc7 : 0x8d;
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if (IsMov)
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*RegSlot = 0xc0 | ((*RegSlot >> 3) & 7);
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else
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*RegSlot = 0x80 | Reg | (Reg << 3);
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relocateOne(Loc, BufEnd, R_386_TLS_LE, P, SA);
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}
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X86_64TargetInfo::X86_64TargetInfo() {
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CopyReloc = R_X86_64_COPY;
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PCRelReloc = R_X86_64_PC32;
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@ -0,0 +1,20 @@
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.type tlsshared0,@object
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.section .tbss,"awT",@nobits
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.globl tlsshared0
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.align 4
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tlsshared0:
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.long 0
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.size tlsshared0, 4
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.type tlsshared1,@object
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.globl tlsshared1
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.align 4
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tlsshared1:
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.long 0
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.size tlsshared1, 4
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.text
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.globl __tls_get_addr
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.align 16, 0x90
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.type __tls_get_addr,@function
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__tls_get_addr:
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@ -0,0 +1,59 @@
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// RUN: llvm-mc -filetype=obj -triple=i686-pc-linux %p/Inputs/tls-opt-gdiele-i686.s -o %tso.o
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// RUN: llvm-mc -filetype=obj -triple=i686-pc-linux %s -o %t.o
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// RUN: ld.lld -shared %tso.o -o %tso
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// RUN: ld.lld %t.o %tso -o %tout
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// RUN: llvm-readobj -r %tout | FileCheck --check-prefix=NORELOC %s
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// RUN: llvm-objdump -d %tout | FileCheck --check-prefix=DISASM %s
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// NORELOC: Relocations [
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// NORELOC-NEXT: Section ({{.*}}) .rel.dyn {
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// NORELOC-NEXT: 0x12050 R_386_TLS_TPOFF tlsshared0 0x0
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// NORELOC-NEXT: 0x12054 R_386_TLS_TPOFF tlsshared1 0x0
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// NORELOC-NEXT: }
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// NORELOC-NEXT: ]
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// DISASM: Disassembly of section .text:
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// DISASM-NEXT: _start:
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// DISASM-NEXT: 11000: 65 a1 00 00 00 00 movl %gs:0, %eax
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// DISASM-NEXT: 11006: 03 83 f8 ff ff ff addl -8(%ebx), %eax
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// DISASM-NEXT: 1100c: 65 a1 00 00 00 00 movl %gs:0, %eax
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// DISASM-NEXT: 11012: 03 83 fc ff ff ff addl -4(%ebx), %eax
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// DISASM-NEXT: 11018: 65 a1 00 00 00 00 movl %gs:0, %eax
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// DISASM-NEXT: 1101e: 81 e8 08 00 00 00 subl $8, %eax
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// DISASM-NEXT: 11024: 65 a1 00 00 00 00 movl %gs:0, %eax
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// DISASM-NEXT: 1102a: 81 e8 04 00 00 00 subl $4, %eax
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.type tlsexe1,@object
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.section .tbss,"awT",@nobits
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.globl tlsexe1
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.align 4
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tlsexe1:
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.long 0
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.size tlsexe1, 4
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.type tlsexe2,@object
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.section .tbss,"awT",@nobits
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.globl tlsexe2
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.align 4
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tlsexe2:
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.long 0
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.size tlsexe2, 4
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.section .text
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.globl ___tls_get_addr
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.type ___tls_get_addr,@function
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___tls_get_addr:
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.section .text
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.globl _start
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_start:
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//GD->IE
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leal tlsshared0@tlsgd(,%ebx,1),%eax
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call ___tls_get_addr@plt
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leal tlsshared1@tlsgd(,%ebx,1),%eax
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call ___tls_get_addr@plt
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//GD->IE
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leal tlsexe1@tlsgd(,%ebx,1),%eax
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call ___tls_get_addr@plt
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leal tlsexe2@tlsgd(,%ebx,1),%eax
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call ___tls_get_addr@plt
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@ -0,0 +1,69 @@
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// RUN: llvm-mc -filetype=obj -triple=i686-pc-linux %s -o %t.o
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// RUN: ld.lld %t.o -o %t1
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// RUN: llvm-readobj -r %t1 | FileCheck --check-prefix=NORELOC %s
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// RUN: llvm-objdump -d %t1 | FileCheck --check-prefix=DISASM %s
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// NORELOC: Relocations [
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// NORELOC-NEXT: ]
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// DISASM: Disassembly of section .text:
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// DISASM-NEXT: _start:
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// LD -> LE:
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// DISASM-NEXT: 11000: 65 a1 00 00 00 00 movl %gs:0, %eax
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// DISASM-NEXT: 11006: 90 nop
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// DISASM-NEXT: 11007: 8d 74 26 00 leal (%esi), %esi
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// DISASM-NEXT: 1100b: 8d 90 f8 ff ff ff leal -8(%eax), %edx
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// DISASM-NEXT: 11011: 65 a1 00 00 00 00 movl %gs:0, %eax
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// DISASM-NEXT: 11017: 90 nop
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// DISASM-NEXT: 11018: 8d 74 26 00 leal (%esi), %esi
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// DISASM-NEXT: 1101c: 8d 90 fc ff ff ff leal -4(%eax), %edx
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// IE -> LE:
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// 4294967288 == 0xFFFFFFF8
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// 4294967292 == 0xFFFFFFFC
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// DISASM-NEXT: 11022: 65 a1 00 00 00 00 movl %gs:0, %eax
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// DISASM-NEXT: 11028: c7 c0 f8 ff ff ff movl $4294967288, %eax
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// DISASM-NEXT: 1102e: 65 a1 00 00 00 00 movl %gs:0, %eax
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// DISASM-NEXT: 11034: c7 c0 fc ff ff ff movl $4294967292, %eax
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// DISASM-NEXT: 1103a: 65 a1 00 00 00 00 movl %gs:0, %eax
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// DISASM-NEXT: 11040: 8d 80 f8 ff ff ff leal -8(%eax), %eax
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// DISASM-NEXT: 11046: 65 a1 00 00 00 00 movl %gs:0, %eax
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// DISASM-NEXT: 1104c: 8d 80 fc ff ff ff leal -4(%eax), %eax
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.type tls0,@object
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.section .tbss,"awT",@nobits
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.globl tls0
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.align 4
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tls0:
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.long 0
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.size tls0, 4
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.type tls1,@object
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.globl tls1
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.align 4
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tls1:
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.long 0
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.size tls1, 4
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.section .text
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.globl ___tls_get_addr
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.type ___tls_get_addr,@function
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___tls_get_addr:
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.section .text
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.globl _start
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_start:
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//LD -> LE:
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leal tls0@tlsldm(%ebx),%eax
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call ___tls_get_addr@plt
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leal tls0@dtpoff(%eax),%edx
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leal tls1@tlsldm(%ebx),%eax
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call ___tls_get_addr@plt
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leal tls1@dtpoff(%eax),%edx
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//IE -> LE:
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movl %gs:0,%eax
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movl tls0@gotntpoff(%ebx),%eax
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movl %gs:0,%eax
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movl tls1@gotntpoff(%ebx),%eax
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movl %gs:0,%eax
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addl tls0@gotntpoff(%ebx),%eax
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movl %gs:0,%eax
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addl tls1@gotntpoff(%ebx),%eax
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