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Target: Stop assigning RELRO sections to .ldata.rel.ro. #137742

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Merged
merged 1 commit into from
Apr 29, 2025
+34 −23
Merged

Target: Stop assigning RELRO sections to .ldata.rel.ro. #137742

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13 changes: 13 additions & 0 deletions llvm/lib/Target/TargetMachine.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -119,6 +119,19 @@ bool TargetMachine::isLargeGlobalValue(const GlobalValue *GVal) const {
GV->getName().starts_with("__start_") ||
GV->getName().starts_with("__stop_")))
return true;
// Linkers do not currently support PT_GNU_RELRO for SHF_X86_64_LARGE
// sections; that would require the linker to emit more than one
// PT_GNU_RELRO because large sections are discontiguous by design, and most
// ELF dynamic loaders do not support that (bionic appears to support it but
// glibc/musl/FreeBSD/NetBSD/OpenBSD appear not to). With current linkers
// these sections will end up in .ldata which results in silently disabling
// RELRO. If this ever gets supported by downstream components in the future
// we could add an opt-in flag for moving these sections to .ldata.rel.ro
// which would trigger the creation of a second PT_GNU_RELRO.
if (!GV->isDeclarationForLinker() &&
TargetLoweringObjectFile::getKindForGlobal(GV, *this)
.isReadOnlyWithRel())
return false;
const DataLayout &DL = GV->getDataLayout();
uint64_t Size = DL.getTypeAllocSize(GV->getValueType());
return Size == 0 || Size > LargeDataThreshold;
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4 changes: 2 additions & 2 deletions llvm/test/CodeGen/X86/code-model-elf-sections.ll
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Expand Up @@ -66,7 +66,7 @@
; LARGE: .lbss {{.*}} WAl {{.*}}
; LARGE: .rodata {{.*}} A {{.*}}
; LARGE: .lrodata {{.*}} Al {{.*}}
; LARGE: .ldata.rel.ro {{.*}} WAl {{.*}}
; LARGE: .data.rel.ro {{.*}} WA {{.*}}
; LARGE: .tbss {{.*}} WAT {{.*}}
; LARGE: .tdata {{.*}} WAT {{.*}}

Expand All @@ -84,7 +84,7 @@
; LARGE-DS: .lbss.bss {{.*}} WAl {{.*}}
; LARGE-DS: .rodata {{.*}} A {{.*}}
; LARGE-DS: .lrodata.rodata {{.*}} Al {{.*}}
; LARGE-DS: .ldata.rel.ro.relro {{.*}} WAl {{.*}}
; LARGE-DS: .data.rel.ro.relro {{.*}} WA {{.*}}
; LARGE-DS: .tbss.tbss {{.*}} WAT {{.*}}
; LARGE-DS: .tdata.tdata {{.*}} WAT {{.*}}

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40 changes: 19 additions & 21 deletions llvm/test/CodeGen/X86/code-model-elf.ll
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Expand Up @@ -50,7 +50,7 @@ target triple = "x86_64--linux"

@global_data = dso_local global [10 x i32] [i32 1, i32 2, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0], align 16
@static_data = internal global [10 x i32] zeroinitializer, align 16
@static_data_alias = internal constant ptr getelementptr inbounds ([10 x i32], ptr @static_data, i64 0, i64 2), align 8
@static_data_relro = internal constant ptr getelementptr inbounds ([10 x i32], ptr @static_data, i64 0, i64 2), align 8
@extern_data = external global [10 x i32], align 16
@thread_data = external thread_local global i32, align 4
@unknown_size_data = dso_local global [0 x i32] zeroinitializer, align 16
Expand Down Expand Up @@ -117,59 +117,57 @@ define dso_local ptr @lea_static_data() #0 {
ret ptr @static_data
}

define dso_local ptr @lea_static_data_alias() #0 {
; SMALL-STATIC-LABEL: lea_static_data_alias:
define dso_local ptr @lea_static_data_relro() #0 {
; SMALL-STATIC-LABEL: lea_static_data_relro:
; SMALL-STATIC: # %bb.0:
; SMALL-STATIC-NEXT: movl $static_data_alias, %eax
; SMALL-STATIC-NEXT: movl $static_data_relro, %eax
; SMALL-STATIC-NEXT: retq
;
; MEDIUM-STATIC-LABEL: lea_static_data_alias:
; MEDIUM-STATIC-LABEL: lea_static_data_relro:
; MEDIUM-STATIC: # %bb.0:
; MEDIUM-STATIC-NEXT: movabsq $static_data_alias, %rax
; MEDIUM-STATIC-NEXT: movabsq $static_data_relro, %rax
; MEDIUM-STATIC-NEXT: retq
;
; LARGE-STATIC-LABEL: lea_static_data_alias:
; LARGE-STATIC-LABEL: lea_static_data_relro:
; LARGE-STATIC: # %bb.0:
; LARGE-STATIC-NEXT: movabsq $static_data_alias, %rax
; LARGE-STATIC-NEXT: movabsq $static_data_relro, %rax
; LARGE-STATIC-NEXT: retq
;
; SMALL-PIC-LABEL: lea_static_data_alias:
; SMALL-PIC-LABEL: lea_static_data_relro:
; SMALL-PIC: # %bb.0:
; SMALL-PIC-NEXT: leaq static_data_alias(%rip), %rax
; SMALL-PIC-NEXT: leaq static_data_relro(%rip), %rax
; SMALL-PIC-NEXT: retq
;
; MEDIUM-SMALL-DATA-PIC-LABEL: lea_static_data_alias:
; MEDIUM-SMALL-DATA-PIC-LABEL: lea_static_data_relro:
; MEDIUM-SMALL-DATA-PIC: # %bb.0:
; MEDIUM-SMALL-DATA-PIC-NEXT: leaq static_data_alias(%rip), %rax
; MEDIUM-SMALL-DATA-PIC-NEXT: leaq static_data_relro(%rip), %rax
; MEDIUM-SMALL-DATA-PIC-NEXT: retq
;
; MEDIUM-PIC-LABEL: lea_static_data_alias:
; MEDIUM-PIC-LABEL: lea_static_data_relro:
; MEDIUM-PIC: # %bb.0:
; MEDIUM-PIC-NEXT: leaq _GLOBAL_OFFSET_TABLE_(%rip), %rcx
; MEDIUM-PIC-NEXT: movabsq $static_data_alias@GOTOFF, %rax
; MEDIUM-PIC-NEXT: addq %rcx, %rax
; MEDIUM-PIC-NEXT: leaq static_data_relro(%rip), %rax
; MEDIUM-PIC-NEXT: retq
;
; LARGE-PIC-LABEL: lea_static_data_alias:
; LARGE-PIC-LABEL: lea_static_data_relro:
; LARGE-PIC: # %bb.0:
; LARGE-PIC-NEXT: .L1$pb:
; LARGE-PIC-NEXT: leaq .L1$pb(%rip), %rax
; LARGE-PIC-NEXT: movabsq $_GLOBAL_OFFSET_TABLE_-.L1$pb, %rcx
; LARGE-PIC-NEXT: addq %rax, %rcx
; LARGE-PIC-NEXT: movabsq $static_data_alias@GOTOFF, %rax
; LARGE-PIC-NEXT: movabsq $static_data_relro@GOTOFF, %rax
; LARGE-PIC-NEXT: addq %rcx, %rax
; LARGE-PIC-NEXT: retq
;
; LARGE-SMALL-DATA-PIC-LABEL: lea_static_data_alias:
; LARGE-SMALL-DATA-PIC-LABEL: lea_static_data_relro:
; LARGE-SMALL-DATA-PIC: # %bb.0:
; LARGE-SMALL-DATA-PIC-NEXT: .L1$pb:
; LARGE-SMALL-DATA-PIC-NEXT: leaq .L1$pb(%rip), %rax
; LARGE-SMALL-DATA-PIC-NEXT: movabsq $_GLOBAL_OFFSET_TABLE_-.L1$pb, %rcx
; LARGE-SMALL-DATA-PIC-NEXT: addq %rax, %rcx
; LARGE-SMALL-DATA-PIC-NEXT: movabsq $static_data_alias@GOTOFF, %rax
; LARGE-SMALL-DATA-PIC-NEXT: movabsq $static_data_relro@GOTOFF, %rax
; LARGE-SMALL-DATA-PIC-NEXT: addq %rcx, %rax
; LARGE-SMALL-DATA-PIC-NEXT: retq
ret ptr @static_data_alias
ret ptr @static_data_relro
}

define dso_local ptr @lea_global_data() #0 {
Expand Down
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