[lld] 99e7350 - IRSymTab: Record _GLOBAL_OFFSET_TABLE_ for ELF x86
via llvm-commits
llvm-commits at lists.llvm.org
Tue Apr 23 17:02:25 PDT 2024
Author: Fangrui Song
Date: 2024-04-23T17:02:21-07:00
New Revision: 99e7350235055654aaa923701bf36adaf01739d0
URL: https://github.com/llvm/llvm-project/commit/99e7350235055654aaa923701bf36adaf01739d0
DIFF: https://github.com/llvm/llvm-project/commit/99e7350235055654aaa923701bf36adaf01739d0.diff
LOG: IRSymTab: Record _GLOBAL_OFFSET_TABLE_ for ELF x86
In ELF, relocatable files generated for x86-32 and some code models of
x86-64 (medium, large) may reference the special symbol
`_GLOBAL_OFFSET_TABLE_` that is not used in the IR. In an LTO link, if
there is no regular relocatable file referencing the special symbol, the
linker may not define the symbol and lead to a spurious "undefined
symbol" error.
Fix #61101: record that `_GLOBAL_OFFSET_TABLE_` is used in the IR symbol
table.
Note: The `PreservedSymbols` mechanism
(https://reviews.llvm.org/D112595) that just sets `FB_used` is not
applicable.
The `getRuntimeLibcallSymbols` for extracting lazy runtime library
symbols is for symbols that are "always" potentially used, but linkers
don't have the code model information to make a precise decision.
Pull Request: https://github.com/llvm/llvm-project/pull/89463
Added:
lld/test/ELF/lto/i386-global-offset-table.ll
lld/test/ELF/lto/x86-64-global-offset-table.ll
Modified:
llvm/lib/Object/ModuleSymbolTable.cpp
llvm/test/LTO/X86/codemodel-2.ll
llvm/test/LTO/X86/codemodel-3.ll
llvm/test/LTO/X86/largedatathreshold-1.ll
llvm/test/LTO/X86/largedatathreshold-2.ll
llvm/test/LTO/X86/largedatathreshold-3.ll
Removed:
################################################################################
diff --git a/lld/test/ELF/lto/i386-global-offset-table.ll b/lld/test/ELF/lto/i386-global-offset-table.ll
new file mode 100644
index 00000000000000..3fa11f6e6d40d7
--- /dev/null
+++ b/lld/test/ELF/lto/i386-global-offset-table.ll
@@ -0,0 +1,29 @@
+; REQUIRES: x86
+;; LTO-generated relocatable files may reference _GLOBAL_OFFSET_TABLE_ while
+;; the IR does not mention _GLOBAL_OFFSET_TABLE_.
+;; Test that there is no spurious "undefined symbol" error.
+
+; RUN: rm -rf %t && mkdir %t && cd %t
+; RUN: llvm-as %s -o a.bc
+; RUN: ld.lld -pie a.bc -o a
+; RUN: llvm-nm a | FileCheck %s
+
+; CHECK: d _GLOBAL_OFFSET_TABLE_
+
+target datalayout = "e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-i128:128-f64:32:64-f80:32-n8:16:32-S128"
+target triple = "i386-pc-linux-gnu"
+
+ at i = global i32 0
+
+define dso_local void @_start() {
+entry:
+ %0 = load i32, ptr @i
+ %inc = add nsw i32 %0, 1
+ store i32 %inc, ptr @i
+ ret void
+}
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = !{i32 8, !"PIC Level", i32 2}
+!1 = !{i32 7, !"PIE Level", i32 2}
diff --git a/lld/test/ELF/lto/x86-64-global-offset-table.ll b/lld/test/ELF/lto/x86-64-global-offset-table.ll
new file mode 100644
index 00000000000000..4b0f638b409e1b
--- /dev/null
+++ b/lld/test/ELF/lto/x86-64-global-offset-table.ll
@@ -0,0 +1,71 @@
+; REQUIRES: x86
+;; LTO-generated relocatable files may reference _GLOBAL_OFFSET_TABLE_ while
+;; the IR does not mention _GLOBAL_OFFSET_TABLE_.
+;; Test that there is no spurious "undefined symbol" error.
+
+; RUN: rm -rf %t && split-file %s %t && cd %t
+; RUN: opt -module-summary b.ll -o b.bc
+
+;; Test Thin LTO.
+; RUN: cat a.ll medium.ll | opt -module-summary - -o medium.bc
+; RUN: ld.lld -pie --no-relax medium.bc b.bc -o medium
+; RUN: llvm-objdump -dt medium | FileCheck %s
+
+;; Test regular LTO.
+; RUN: cat a.ll large.ll | llvm-as - -o large.bc
+; RUN: ld.lld -pie large.bc b.bc -o large
+; RUN: llvm-objdump -dt large | FileCheck %s
+
+;; Explicit reference of _GLOBAL_OFFSET_TABLE_ is fine.
+; RUN: cat a.ll medium.ll ref.ll | opt -module-summary - -o ref.bc
+; RUN: ld.lld -pie -u ref ref.bc b.bc -y _GLOBAL_OFFSET_TABLE_ -o ref 2>&1 | FileCheck %s --check-prefix=TRACE
+; RUN: llvm-objdump -dt ref | FileCheck %s
+
+; TRACE: ref.bc: reference to _GLOBAL_OFFSET_TABLE_
+; TRACE-NEXT: ref.bc: reference to _GLOBAL_OFFSET_TABLE_
+; TRACE-NEXT: <internal>: definition of _GLOBAL_OFFSET_TABLE_
+; TRACE-NEXT: ref.lto.ref.o: reference to _GLOBAL_OFFSET_TABLE_
+
+;; The IR symbol table references _GLOBAL_OFFSET_TABLE_, which causes lld to define the symbol.
+; CHECK: .got.plt 0000000000000000 .hidden _GLOBAL_OFFSET_TABLE_
+; CHECK: movabsq
+
+;--- a.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at i = external global i32
+
+define dso_local void @_start() {
+entry:
+ %0 = load i32, ptr @i
+ %inc = add nsw i32 %0, 1
+ store i32 %inc, ptr @i
+ ret void
+}
+
+!llvm.module.flags = !{!0, !1, !2, !3}
+
+!0 = !{i32 8, !"PIC Level", i32 2}
+!1 = !{i32 7, !"PIE Level", i32 2}
+!2 = !{i32 1, !"Large Data Threshold", i64 0}
+
+;--- medium.ll
+!3 = !{i32 1, !"Code Model", i32 3}
+
+;--- large.ll
+!3 = !{i32 1, !"Code Model", i32 4}
+
+;--- ref.ll
+ at _GLOBAL_OFFSET_TABLE_ = external global [0 x i8]
+
+define dso_local ptr @ref() {
+entry:
+ ret ptr @_GLOBAL_OFFSET_TABLE_
+}
+
+;--- b.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at i = global i32 0
diff --git a/llvm/lib/Object/ModuleSymbolTable.cpp b/llvm/lib/Object/ModuleSymbolTable.cpp
index 07f76688fa43e7..d8f520ad02c2f2 100644
--- a/llvm/lib/Object/ModuleSymbolTable.cpp
+++ b/llvm/lib/Object/ModuleSymbolTable.cpp
@@ -175,6 +175,20 @@ void ModuleSymbolTable::CollectAsmSymbols(
AsmSymbol(Key, BasicSymbolRef::Flags(Res));
}
});
+
+ // In ELF, object code generated for x86-32 and some code models of x86-64 may
+ // reference the special symbol _GLOBAL_OFFSET_TABLE_ that is not used in the
+ // IR. Record it like inline asm symbols.
+ Triple TT(M.getTargetTriple());
+ if (!TT.isOSBinFormatELF() || !TT.isX86())
+ return;
+ auto CM = M.getCodeModel();
+ if (TT.getArch() == Triple::x86 || CM == CodeModel::Medium ||
+ CM == CodeModel::Large) {
+ AsmSymbol("_GLOBAL_OFFSET_TABLE_",
+ BasicSymbolRef::Flags(BasicSymbolRef::SF_Undefined |
+ BasicSymbolRef::SF_Global));
+ }
}
void ModuleSymbolTable::CollectAsmSymvers(
diff --git a/llvm/test/LTO/X86/codemodel-2.ll b/llvm/test/LTO/X86/codemodel-2.ll
index 5cd9731606f2bd..fc1074bcf2235c 100644
--- a/llvm/test/LTO/X86/codemodel-2.ll
+++ b/llvm/test/LTO/X86/codemodel-2.ll
@@ -1,5 +1,5 @@
; RUN: llvm-as %s -o %t.o
-; RUN: llvm-lto2 run -r %t.o,_start,px %t.o -o %t.s
+; RUN: llvm-lto2 run -r %t.o,_start,px -r %t.o,_GLOBAL_OFFSET_TABLE_, %t.o -o %t.s
; RUN: llvm-objdump --no-print-imm-hex -d %t.s.0 | FileCheck %s --check-prefix=CHECK-LARGE
target triple = "x86_64-unknown-linux-gnu"
diff --git a/llvm/test/LTO/X86/codemodel-3.ll b/llvm/test/LTO/X86/codemodel-3.ll
index 947221e9f36dc5..13702dfbca2da4 100644
--- a/llvm/test/LTO/X86/codemodel-3.ll
+++ b/llvm/test/LTO/X86/codemodel-3.ll
@@ -1,6 +1,7 @@
; RUN: llvm-as %s -o %t0.o
; RUN: llvm-as < %p/Inputs/codemodel-3.ll > %t1.o
-; RUN: not llvm-lto2 run -r %t0.o,_start,px -r %t1.o,bar,px %t0.o %t1.o -o %t2.s 2>&1 | FileCheck %s
+; RUN: not llvm-lto2 run -r %t0.o,_start,px -r %t1.o,bar,px -r %t0.o,_GLOBAL_OFFSET_TABLE_, \
+; RUN: -r %t1.o,_GLOBAL_OFFSET_TABLE_, %t0.o %t1.o -o %t2.s 2>&1 | FileCheck %s
target triple = "x86_64-unknown-linux-gnu"
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
diff --git a/llvm/test/LTO/X86/largedatathreshold-1.ll b/llvm/test/LTO/X86/largedatathreshold-1.ll
index e3be5c11baaac2..dfd8319511b617 100644
--- a/llvm/test/LTO/X86/largedatathreshold-1.ll
+++ b/llvm/test/LTO/X86/largedatathreshold-1.ll
@@ -1,5 +1,5 @@
; RUN: llvm-as %s -o %t.o
-; RUN: llvm-lto2 run -r %t.o,_start,px %t.o -o %t.s
+; RUN: llvm-lto2 run -r %t.o,_start,px -r %t.o,_GLOBAL_OFFSET_TABLE_, %t.o -o %t.s
; RUN: llvm-objdump -d %t.s.0 | FileCheck %s
target triple = "x86_64-unknown-linux-gnu"
diff --git a/llvm/test/LTO/X86/largedatathreshold-2.ll b/llvm/test/LTO/X86/largedatathreshold-2.ll
index 103c066b744d0f..59438bbdb5027f 100644
--- a/llvm/test/LTO/X86/largedatathreshold-2.ll
+++ b/llvm/test/LTO/X86/largedatathreshold-2.ll
@@ -1,5 +1,5 @@
; RUN: llvm-as %s -o %t.o
-; RUN: llvm-lto2 run -r %t.o,_start,px %t.o -o %t.s
+; RUN: llvm-lto2 run -r %t.o,_start,px -r %t.o,_GLOBAL_OFFSET_TABLE_, %t.o -o %t.s
; RUN: llvm-objdump -d %t.s.0 | FileCheck %s
target triple = "x86_64-unknown-linux-gnu"
diff --git a/llvm/test/LTO/X86/largedatathreshold-3.ll b/llvm/test/LTO/X86/largedatathreshold-3.ll
index 3c0653db334d85..fea7987ff15566 100644
--- a/llvm/test/LTO/X86/largedatathreshold-3.ll
+++ b/llvm/test/LTO/X86/largedatathreshold-3.ll
@@ -1,6 +1,7 @@
; RUN: llvm-as %s -o %t0.o
; RUN: llvm-as < %p/Inputs/largedatathreshold.ll > %t1.o
-; RUN: not llvm-lto2 run -r %t0.o,_start,px -r %t1.o,bar,px %t0.o %t1.o -o %t2.s 2>&1 | FileCheck %s
+; RUN: not llvm-lto2 run -r %t0.o,_start,px -r %t1.o,bar,px -r %t0.o,_GLOBAL_OFFSET_TABLE_, \
+; RUN: -r %t1.o,_GLOBAL_OFFSET_TABLE_, %t0.o %t1.o -o %t2.s 2>&1 | FileCheck %s
; CHECK: 'Large Data Threshold': IDs have conflicting values
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