[llvm] e3c2faa - Revert "[X86] Revert -fno-plt __tls_get_addr workaround for old GNU ld"

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2023-01-06T09:43:47+01:00
New Revision: e3c2faa64a55a759b8d780d78221011e35f748d2

URL: https://github.com/llvm/llvm-project/commit/e3c2faa64a55a759b8d780d78221011e35f748d2
DIFF: https://github.com/llvm/llvm-project/commit/e3c2faa64a55a759b8d780d78221011e35f748d2.diff

LOG: Revert "[X86] Revert -fno-plt __tls_get_addr workaround for old GNU ld"

This reverts commit 2679e8bba3e166e3174971d040b9457ec7b7d768.

This change is a significant backwards-compatibility break, which
does in fact break the entire Rust ecosystem, which uses an
-fno-plt -mrelax-relocations=0 default.

Please go through pre-commit review for this change in order to
gain broader consensus.

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86MCInstLower.cpp
    llvm/test/CodeGen/X86/tls-no-plt.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index 9f59132d1176e..9fb97df01b081 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -1024,7 +1024,14 @@ void X86AsmPrinter::LowerTlsAddr(X86MCInstLower &MCInstLowering,
 
   const MCSymbolRefExpr *Sym = MCSymbolRefExpr::create(
       MCInstLowering.GetSymbolFromOperand(MI.getOperand(3)), SRVK, Ctx);
-  const bool UseGot = MMI->getModule()->getRtLibUseGOT();
+
+  // As of binutils 2.32, ld has a bogus TLS relaxation error when the GD/LD
+  // code sequence using R_X86_64_GOTPCREL (instead of R_X86_64_GOTPCRELX) is
+  // attempted to be relaxed to IE/LE (binutils PR24784). Work around the bug by
+  // only using GOT when GOTPCRELX is enabled.
+  // TODO Delete the workaround when GOTPCRELX becomes commonplace.
+  bool UseGot = MMI->getModule()->getRtLibUseGOT() &&
+                Ctx.getAsmInfo()->canRelaxRelocations();
 
   if (Is64Bits) {
     bool NeedsPadding = SRVK == MCSymbolRefExpr::VK_TLSGD;

diff  --git a/llvm/test/CodeGen/X86/tls-no-plt.ll b/llvm/test/CodeGen/X86/tls-no-plt.ll
index 5ca9448e011e3..b076a77e8adb9 100644
--- a/llvm/test/CodeGen/X86/tls-no-plt.ll
+++ b/llvm/test/CodeGen/X86/tls-no-plt.ll
@@ -1,5 +1,10 @@
-; RUN: llc < %s -mtriple=i386-linux-musl -relocation-model=pic | FileCheck --check-prefixes=CHECK,X86 %s
-; RUN: llc < %s -mtriple=x86_64-linux-musl -relocation-model=pic | FileCheck --check-prefixes=CHECK,X64 %s
+; RUN: llc < %s -mtriple=i386-linux-musl -relocation-model=pic -relax-elf-relocations=true | FileCheck --check-prefixes=CHECK,X86 %s
+; RUN: llc < %s -mtriple=x86_64-linux-musl -relocation-model=pic -relax-elf-relocations=true | FileCheck --check-prefixes=CHECK,X64 %s
+
+;; If GOTPCRELX is disabled, don't use GOT for __tls_get_addr to work around
+;; a ld.bfd bug (binutils PR24784).
+; RUN: llc < %s -mtriple=i386-linux-musl -relocation-model=pic -relax-elf-relocations=false | FileCheck --check-prefixes=CHECK,X86-PLT %s
+; RUN: llc < %s -mtriple=x86_64-linux-musl -relocation-model=pic -relax-elf-relocations=false | FileCheck --check-prefixes=CHECK,X64-PLT %s
 
 @gd = thread_local global i32 0
 @ld = internal thread_local global i32 0
@@ -9,9 +14,11 @@ entry:
 ; CHECK-LABEL: get_gd:
 ; X86: leal gd at TLSGD(%ebx), %eax
 ; X86: calll *___tls_get_addr at GOT(%ebx)
+; X86-PLT: calll ___tls_get_addr at PLT
 
 ; X64: leaq gd at TLSGD(%rip), %rdi
 ; X64: callq *__tls_get_addr at GOTPCREL(%rip)
+; X64-PLT: callq __tls_get_addr at PLT
   ret ptr @gd
 }
 
@@ -20,9 +27,11 @@ define ptr @get_ld() {
 ; CHECK-LABEL: get_ld:
 ; X86: leal ld at TLSLDM(%ebx), %eax
 ; X86: calll *___tls_get_addr at GOT(%ebx)
+; X86-PLT: calll ___tls_get_addr at PLT
 
 ; X64: leaq ld at TLSLD(%rip), %rdi
 ; X64: callq *__tls_get_addr at GOTPCREL(%rip)
+; X64-PLT: callq __tls_get_addr at PLT
   ret ptr @ld
 }