Add a file comment about the Ulrich's document and don't repeat it in other comments.
llvm-svn: 267261
This commit is contained in:
Rui Ueyama
parent
209f6cb055
commit
55274e3fcb
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@ -13,6 +13,15 @@
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// Refer the ELF spec for the single letter varaibles, S, A or P, used
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// in this file.
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//
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// Some functions defined in this file has "relaxTls" as part of their names.
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// They do peephole optimization for TLS variables by rewriting instructions.
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// They are not part of the ABI but optional optimization, so you can skip
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// them if you are not interested in how TLS variables are optimized.
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// See the following paper for the details.
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//
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// Ulrich Drepper, ELF Handling For Thread-Local Storage
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// http://www.akkadia.org/drepper/tls.pdf
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//
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//===----------------------------------------------------------------------===//
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#include "Target.h"
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@ -430,15 +439,12 @@ void X86TargetInfo::relocateOne(uint8_t *Loc, uint32_t Type,
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void X86TargetInfo::relaxTlsGdToLe(uint8_t *Loc, uint32_t Type,
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uint64_t Val) const {
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// GD can be optimized to LE:
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// Convert
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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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// 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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// subl $x@ntpoff,%eax
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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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@ -447,16 +453,14 @@ void X86TargetInfo::relaxTlsGdToLe(uint8_t *Loc, uint32_t Type,
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relocateOne(Loc + 5, R_386_32, Out<ELF32LE>::TlsPhdr->p_memsz - Val);
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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::relaxTlsGdToIe(uint8_t *Loc, uint32_t Type,
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uint64_t Val) const {
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// Convert
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// leal x@tlsgd(, %ebx, 1),
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// call __tls_get_addr@plt
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// to
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// movl %gs:0, %eax
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// addl x@gotntpoff(%ebx), %eax
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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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@ -468,9 +472,6 @@ void X86TargetInfo::relaxTlsGdToIe(uint8_t *Loc, uint32_t Type,
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// In some conditions, relocations can be optimized to avoid using GOT.
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// This function does that for Initial Exec to Local Exec case.
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// Read "ELF Handling For Thread-Local Storage, 5.1
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// 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::relaxTlsIeToLe(uint8_t *Loc, uint32_t Type,
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uint64_t Val) const {
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// Ulrich's document section 6.2 says that @gotntpoff can
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@ -516,10 +517,10 @@ void X86TargetInfo::relaxTlsLdToLe(uint8_t *Loc, uint32_t Type,
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return;
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}
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// LD can be optimized to LE:
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// Convert
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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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// 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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@ -660,19 +661,17 @@ bool X86_64TargetInfo::isRelRelative(uint32_t Type) const {
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}
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}
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// "Ulrich Drepper, ELF Handling For Thread-Local Storage" (5.5
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// x86-x64 linker optimizations, http://www.akkadia.org/drepper/tls.pdf) shows
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// how GD can be optimized to LE:
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// .byte 0x66
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// leaq x@tlsgd(%rip), %rdi
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// .word 0x6666
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// rex64
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// call __tls_get_addr@plt
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// Is converted to:
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// mov %fs:0x0,%rax
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// lea x@tpoff,%rax
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void X86_64TargetInfo::relaxTlsGdToLe(uint8_t *Loc, uint32_t Type,
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uint64_t Val) const {
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// Convert
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// .byte 0x66
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// leaq x@tlsgd(%rip), %rdi
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// .word 0x6666
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// rex64
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// call __tls_get_addr@plt
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// to
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// mov %fs:0x0,%rax
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// lea x@tpoff,%rax
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const uint8_t Inst[] = {
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0x64, 0x48, 0x8b, 0x04, 0x25, 0x00, 0x00, 0x00, 0x00, // mov %fs:0x0,%rax
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0x48, 0x8d, 0x80, 0x00, 0x00, 0x00, 0x00 // lea x@tpoff,%rax
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@ -682,19 +681,17 @@ void X86_64TargetInfo::relaxTlsGdToLe(uint8_t *Loc, uint32_t Type,
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Val + 4 - Out<ELF64LE>::TlsPhdr->p_memsz);
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}
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// "Ulrich Drepper, ELF Handling For Thread-Local Storage" (5.5
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// x86-x64 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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// .byte 0x66
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// leaq x@tlsgd(%rip), %rdi
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// .word 0x6666
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// rex64
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// call __tls_get_addr@plt
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// Is converted to:
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// mov %fs:0x0,%rax
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// addq x@tpoff,%rax
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void X86_64TargetInfo::relaxTlsGdToIe(uint8_t *Loc, uint32_t Type,
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uint64_t Val) const {
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// Convert
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// .byte 0x66
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// leaq x@tlsgd(%rip), %rdi
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// .word 0x6666
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// rex64
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// call __tls_get_addr@plt
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// to
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// mov %fs:0x0,%rax
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// addq x@tpoff,%rax
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const uint8_t Inst[] = {
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0x64, 0x48, 0x8b, 0x04, 0x25, 0x00, 0x00, 0x00, 0x00, // mov %fs:0x0,%rax
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0x48, 0x03, 0x05, 0x00, 0x00, 0x00, 0x00 // addq x@tpoff,%rax
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@ -705,9 +702,6 @@ void X86_64TargetInfo::relaxTlsGdToIe(uint8_t *Loc, uint32_t Type,
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// In some conditions, R_X86_64_GOTTPOFF relocation can be optimized to
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// R_X86_64_TPOFF32 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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// 5.5 x86-x64 linker optimizations" (http://www.akkadia.org/drepper/tls.pdf)
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// by Ulrich Drepper for details.
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void X86_64TargetInfo::relaxTlsIeToLe(uint8_t *Loc, uint32_t Type,
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uint64_t Val) const {
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// Ulrich's document section 6.5 says that @gottpoff(%rip) must be
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@ -722,6 +716,7 @@ void X86_64TargetInfo::relaxTlsIeToLe(uint8_t *Loc, uint32_t Type,
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uint8_t Reg = Loc[-1] >> 3;
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bool IsMov = *Inst == 0x8b;
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bool RspAdd = !IsMov && Reg == 4;
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// r12 and rsp registers requires special handling.
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// Problem is that for other registers, for example leaq 0xXXXXXXXX(%r11),%r11
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// result out is 7 bytes: 4d 8d 9b XX XX XX XX,
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@ -738,19 +733,17 @@ void X86_64TargetInfo::relaxTlsIeToLe(uint8_t *Loc, uint32_t Type,
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relocateOne(Loc, R_X86_64_TPOFF32, Val + 4 - Out<ELF64LE>::TlsPhdr->p_memsz);
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}
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// "Ulrich Drepper, ELF Handling For Thread-Local Storage" (5.5
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// x86-x64 linker optimizations, http://www.akkadia.org/drepper/tls.pdf) shows
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// how LD can be optimized to LE:
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// leaq bar@tlsld(%rip), %rdi
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// callq __tls_get_addr@PLT
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// leaq bar@dtpoff(%rax), %rcx
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// Is converted to:
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// .word 0x6666
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// .byte 0x66
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// mov %fs:0,%rax
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// leaq bar@tpoff(%rax), %rcx
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void X86_64TargetInfo::relaxTlsLdToLe(uint8_t *Loc, uint32_t Type,
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uint64_t Val) const {
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// Convert
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// leaq bar@tlsld(%rip), %rdi
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// callq __tls_get_addr@PLT
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// leaq bar@dtpoff(%rax), %rcx
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// to
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// .word 0x6666
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// .byte 0x66
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// mov %fs:0,%rax
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// leaq bar@tpoff(%rax), %rcx
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if (Type == R_X86_64_DTPOFF64) {
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write64le(Loc, Val - Out<ELF64LE>::TlsPhdr->p_memsz);
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return;
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