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[X86] Fix R_X86_64_TPOFF32 against weak undefined TLS symbols #1646

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[X86] Fix R_X86_64_TPOFF32 against weak undefined TLS symbols #1646

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7 changes: 7 additions & 0 deletions lib/Target/X86/x86_64Relocator.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -752,6 +752,13 @@ Relocator::Result eld::relocTPOFF(Relocation &pReloc, x86_64Relocator &pParent,

uint64_t TLSTemplateSize = pParent.getTarget().getTLSTemplateSize();

ResolveInfo *rsym = pReloc.symInfo();
if (rsym && rsym->isWeakUndef() &&
(pParent.config().codeGenType() == LinkerConfig::Exec)) {
Relocator::DWord A = pReloc.addend();
return ApplyReloc(pReloc, A, pRelocDesc, DiagEngine, options, pParent);
}

@quic-seaswara Shankar Easwaran (quic-seaswara) Aug 7, 2026

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What about shared/pie ?

what is the difference for other targets ?

@rachitmeht Rachit Mehta (rachitmeht) Aug 7, 2026

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TPOFF handling for Weak undef is not done for other architectures also.

@rachitmeht Rachit Mehta (rachitmeht) Aug 7, 2026

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I copied the check from relocAbs(), it mentions that weak-undef symbol resolving to 0 is only the correct link-time behavior in a static executable. So, for a shared/PIE, an unresolved symbol should be handled via dynamic relocations.


if (TLSTemplateSize == 0) {
pParent.config().raise(Diag::no_pt_tls_segment);
return Relocator::BadReloc;
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11 changes: 11 additions & 0 deletions test/x86_64/linux/WeakUndefTLS/Inputs/weak_tls_defined.s
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Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
.section .tdata, "awT", @progbits
.align 4
.global real_tls
real_tls:
.long 0

.section .data
.align 4
result:
.long 0xdeadbeef
.reloc result, R_X86_64_TPOFF32, real_tls
6 changes: 6 additions & 0 deletions test/x86_64/linux/WeakUndefTLS/Inputs/weak_tls_ld.s
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@@ -0,0 +1,6 @@
.weak weak_tls
.section .data
.align 4
result:
.long 0xdeadbeef
.reloc result, R_X86_64_DTPOFF32, weak_tls
6 changes: 6 additions & 0 deletions test/x86_64/linux/WeakUndefTLS/Inputs/weak_tls_ld64.s
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@@ -0,0 +1,6 @@
.weak weak_tls
.section .data
.align 8
result:
.quad 0xdeadbeefdeadbeef
.reloc result, R_X86_64_DTPOFF64, weak_tls
6 changes: 6 additions & 0 deletions test/x86_64/linux/WeakUndefTLS/Inputs/weak_tls_le.s
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@@ -0,0 +1,6 @@
.weak weak_tls
.section .data
.align 4
result:
.long 0xdeadbeef
.reloc result, R_X86_64_TPOFF32, weak_tls
6 changes: 6 additions & 0 deletions test/x86_64/linux/WeakUndefTLS/Inputs/weak_tls_le64.s
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@@ -0,0 +1,6 @@
.weak weak_tls
.section .data
.align 8
result:
.quad 0xdeadbeefdeadbeef
.reloc result, R_X86_64_TPOFF64, weak_tls
6 changes: 6 additions & 0 deletions test/x86_64/linux/WeakUndefTLS/Inputs/weak_tls_le_addend.s
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@@ -0,0 +1,6 @@
.weak weak_tls
.section .data
.align 4
result:
.long 0xdeadbeef
.reloc result, R_X86_64_TPOFF32, weak_tls+2
61 changes: 61 additions & 0 deletions test/x86_64/linux/WeakUndefTLS/WeakUndefTLS.test
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@@ -0,0 +1,61 @@
#--WeakUndefTLS.test----------Executable--------#
BEGIN_COMMENT
# Test R_X86_64_TPOFF32/64 and R_X86_64_DTPOFF32/64 relocations against
# weak undefined TLS symbols. A weak undefined TLS symbol has no TLS slot,
# so the tpoff formula must not run; the result is the addend only (= 0
# for the common case). Mirrors lld's R_TPREL guard:
# if (sym.isUndefined()) return a;
# Also verifies that defined TLS symbols are unaffected (regression guard).
#END_COMMENT

#START_TEST

# Case 1: TPOFF32 + weak-undef -> 0x00000000
RUN: %clang %clangopts -c %p/Inputs/weak_tls_le.s -o %t.le.o
RUN: %link %linkopts -static %t.le.o -o %t.le.exe
RUN: %objdump -s -j .data %t.le.exe | %filecheck %s --check-prefix=LE32

# Case 2: TPOFF64 + weak-undef -> 0x0000000000000000
RUN: %clang %clangopts -c %p/Inputs/weak_tls_le64.s -o %t.le64.o
RUN: %link %linkopts -static %t.le64.o -o %t.le64.exe
RUN: %objdump -s -j .data %t.le64.exe | %filecheck %s --check-prefix=LE64

# Case 3: DTPOFF32 + weak-undef -> 0x00000000
RUN: %clang %clangopts -c %p/Inputs/weak_tls_ld.s -o %t.ld.o
RUN: %link %linkopts -static %t.ld.o -o %t.ld.exe
RUN: %objdump -s -j .data %t.ld.exe | %filecheck %s --check-prefix=LD32

# Case 4: DTPOFF64 + weak-undef -> 0x0000000000000000
RUN: %clang %clangopts -c %p/Inputs/weak_tls_ld64.s -o %t.ld64.o
RUN: %link %linkopts -static %t.ld64.o -o %t.ld64.exe
RUN: %objdump -s -j .data %t.ld64.exe | %filecheck %s --check-prefix=LD64

# Case 5: TPOFF32 + defined symbol -> -4 = 0xfffffffc (regression guard)
RUN: %clang %clangopts -c %p/Inputs/weak_tls_defined.s -o %t.def.o
RUN: %link %linkopts -static %t.def.o -o %t.def.exe
RUN: %objdump -s -j .data %t.def.exe | %filecheck %s --check-prefix=DEFINED

# Case 6: TPOFF32 + weak-undef + addend=2 -> 0x00000002
RUN: %clang %clangopts -c %p/Inputs/weak_tls_le_addend.s -o %t.addend.o
RUN: %link %linkopts -static %t.addend.o -o %t.addend.exe
RUN: %objdump -s -j .data %t.addend.exe | %filecheck %s --check-prefix=ADDEND

LE32: Contents of section .data:
LE32-NEXT: {{[0-9a-f]+}} 00000000

LE64: Contents of section .data:
LE64-NEXT: {{[0-9a-f]+}} 00000000 00000000

LD32: Contents of section .data:
LD32-NEXT: {{[0-9a-f]+}} 00000000

LD64: Contents of section .data:
LD64-NEXT: {{[0-9a-f]+}} 00000000 00000000

DEFINED: Contents of section .data:
DEFINED-NEXT: {{[0-9a-f]+}} fcffffff

ADDEND: Contents of section .data:
ADDEND-NEXT: {{[0-9a-f]+}} 02000000

#END_TEST