[X86_64] Emit _GLOBAL_OFFSET_TABLE_ symbol for x86-64 by deepakshirkem · Pull Request #1123 · qualcomm/eld

deepakshirkem · 2026-05-02T20:38:00Z

Problem

ELD does not emit the GLOBAL_OFFSET_TABLE symbol for x86-64, causing an undefined reference error when object files reference this symbol. This affects code compiled with -fPIC or using the large code model.

Error: 1.o(.data+0x0): undefined reference to `_GLOBAL_OFFSET_TABLE_'
Fatal: Linking had errors.

Fix

Add GLOBAL_OFFSET_TABLE symbol support to the x86-64 backend following the same pattern used by other backends:

initTargetSymbols(): Register the symbol as AsReferred so it is only defined if actually referenced by input files.
defineGOTSymbol(): Bind the symbol to the first fragment of .got.plt so it points to the GOT base address.
finalizeScanRelocations(): Call defineGOTSymbol() after all relocations have been scanned and .got.plt is populated.

Testing

Added test/X86/standalone/GlobalOffsetTable/GlobalOffsetTable.test that verifies GLOBAL_OFFSET_TABLE is emitted and points to .got.plt.

Fixes #570.

cc @quic-seaswara

quic-seaswara · 2026-05-04T23:37:29Z

+              0x0, // value
+              FragmentRef::null(), ResolveInfo::Hidden);
+  if (m_pGOTSymbol)
+    m_pGOTSymbol->setShouldIgnore(false);


Can you check the behavior of bfd and lld that we are doing the same ?

quic-seaswara · 2026-05-04T23:38:13Z

@@ -0,0 +1,11 @@
+#----------GlobalOffsetTable.test--------------------- Executable ------#
+#BEGIN_COMMENT


Does this test make sense to be part of Common ?

Can you add a test with linker script with GOT/GOT.PLT discarded and see the behavior ?

Moved to Common/standalone/GlobalOffsetTable/
Added Common/standalone/GlobalOffsetTableDiscard/

quic-seaswara · 2026-05-04T23:38:23Z

+
+int *v = &_GLOBAL_OFFSET_TABLE_;
+
+int a;


initialize variable

deepakshirkem · 2026-05-05T21:10:22Z

Hi @quic-seaswara, Please go one more time.

deepakshirkem · 2026-05-06T05:10:08Z

Hi @parth-07, Please review these changes when you get a chance? Also, if possible, could you re-run the pipeline?

parth-07

What should be the value of _GLOBAL_OFFSET_TABLE_ when there is no .got.plt section?

Example:

#!/usr/bin/env bash

cat >1.c <<\EOF
extern int _GLOBAL_OFFSET_TABLE_;
int foo() { return 1; }
int bar() { return 3; }
int *u = &_GLOBAL_OFFSET_TABLE_;
EOF

LDs=(ld.eld ld.lld ld.bfd)
SFs=(eld lld bfd)

clang -o 1.o -target x86_64-linux-gnu 1.c -c -fPIC

for i in "${!SFs[@]}"; do
  ${LDs[$i]} -o lib1.${SFs[$i]}.so 1.o -shared
done

For this example, eld shared library has _GLOBAL_OFFSET_TABLE_ defined to 0 whereas lld and bfd have valid GLOBAL_OFFSET_TABLE_. Can you please look into it?

Additionally, we need to document the behavior for the properties(local, default vs hidden visibility, NOTYPE vs OBJECT ...) of the _GLOBAL_OFFSET_TABLE_ symbol.

deepakshirkem · 2026-05-06T16:23:18Z

Hi @parth-07, Please go one more time.

quic-seaswara · 2026-05-06T19:35:24Z

+RUN: %link %linkopts %t1.o -o %t1.so -shared 2>&1
+RUN: %readelf -s %t1.so | %filecheck %s
+#END_TEST
+CHECK: {{[1-9][0-9a-f]+}}{{.*}}OBJECT{{.*}}LOCAL{{.*}}HIDDEN{{.*}}_GLOBAL_OFFSET_TABLE_


it would be great if the test can be improved to point to the section as intended.

deepakshirkem · 2026-05-06T19:44:25Z

Hi @quic-seaswara, test has been updated. Please take a look?

quic-seaswara · 2026-05-06T20:03:50Z

What should be the value of _GLOBAL_OFFSET_TABLE_ when there is no .got.plt section?

Example:
#!/usr/bin/env bash

cat >1.c <<\EOF
extern int _GLOBAL_OFFSET_TABLE_;
int foo() { return 1; }
int bar() { return 3; }
int *u = &_GLOBAL_OFFSET_TABLE_;
EOF

LDs=(ld.eld ld.lld ld.bfd)
SFs=(eld lld bfd)

clang -o 1.o -target x86_64-linux-gnu 1.c -c -fPIC

for i in "${!SFs[@]}"; do
  ${LDs[$i]} -o lib1.${SFs[$i]}.so 1.o -shared
done
For this example, eld shared library has _GLOBAL_OFFSET_TABLE_ defined to 0 whereas lld and bfd have valid GLOBAL_OFFSET_TABLE_. Can you please look into it?

Additionally, we need to document the behavior for the properties(local, default vs hidden visibility, NOTYPE vs OBJECT ...) of the _GLOBAL_OFFSET_TABLE_ symbol.

@deepakshirkem can you add a test for this case ?

deepakshirkem · 2026-05-06T20:15:38Z

Hi @quic-seaswara, Can you please re-run the pipeline. I forgot to add specific target on that test.

quic-seaswara · 2026-05-06T20:29:51Z

+# relocations. ELD was incorrectly emitting value 0x0 in this case.
+#END_COMMENT
+#START_TEST
+REQUIRES: x86


move REQUIRES to the top.

quic-seaswara · 2026-05-06T20:31:20Z

+#START_TEST
+REQUIRES: x86
+RUN: %clang %clangopts -c %p/Inputs/1.c -o %t1.o -fPIC -ffunction-sections
+RUN: %link %linkopts %t1.o -o %t1.so -shared 2>&1


What if it is a non shared library link, can we also test for -pie ?

There is no .got.plt so what does GLOBAL_OFFSET_TABLE point to ?

Hi @quic-seaswara, Thank you. I tested both the -pie and shared both are correctly point .got.plt. Adding new test for -pie.

quic-areg

The tests should live under test/X86, not test/Common

deepakshirkem · 2026-05-06T20:47:11Z

Hi @quic-areg, Moving all test in test/X86

deepakshirkem · 2026-05-06T21:00:51Z

Hi @quic-seaswara / @quic-areg, Please take another look when you get a chance? Thank you.

quic-seaswara · 2026-05-06T21:26:48Z

@@ -0,0 +1,14 @@
+REQUIRES: x86


Remove REQUIRES: x86 and move it to Common ?

Hi @quic-seaswara, should I move only GlobalOffsetTableShared to Common, or all the tests we created? Also, if I remove REQUIRES: x86, this test will fail in CI because the fix is currently only implemented in x86_64LDBackend.cpp.

deepakshirkem · 2026-05-07T19:21:42Z

Hi @quic-areg / @quic-seaswara , Can you go one more time. Please re-run the pipeline whenever you get chance.

parth-07 · 2026-05-08T10:09:58Z

+RUN: %clang %clangopts -c %p/Inputs/1.c -o %t1.o -fPIC -ffunction-sections
+RUN: %not %link %linkopts -T %p/Inputs/discard.t %t1.o -o %t1.out 2>&1 | %filecheck %s
+#END_TEST
+CHECK: symbol '_GLOBAL_OFFSET_TABLE_' referenced


What is the error message emitted by eld in this case? Can you please add that as part of the test?

parth-07 · 2026-05-08T10:11:59Z

+RUN: %link %linkopts %t1.o -o %t1.out 2>&1
+RUN: %readelf -S -W -s %t1.out 2>&1 | %filecheck %s
+#END_TEST
+CHECK: .got.plt PROGBITS [[ADDR:[xa-f0-9]+]]


Can you please add a check in the test that makes sure that the ADDR is a non-zero value?

deepakshirkem · 2026-05-08T12:46:13Z

Hi @parth-07, Please go one more time.

deepakshirkem · 2026-05-12T11:33:35Z

Hi @parth-07 / @quic-areg / @quic-seaswara, if you get a chance today to review these changes, please take a look.

deepakshirkem · 2026-05-13T21:01:01Z

Hi @quic-seaswara, Can you please run this pipeline one more time.

deepakshirkem · 2026-05-13T22:13:49Z

Hi @quic-seaswara, The tests in test/x86/standalone/ are being run by the ARM CI and failing since they are x86-specific. Please let me know the correct location for this test? That would be really helpful.

parth-07

Why are we using a new directory test/X86 instead of using the already existing directory test/x86_64?

deepakshirkem · 2026-05-14T17:02:05Z

Hi @quic-seaswara / @parth-07 / @quic-areg, Please review one more time and re- run the pipeline.

deepakshirkem · 2026-05-20T22:13:23Z

Hi @quic-seaswara, Check the updated commit? I have removed the duplicate code. Please run the pipeline? I want to confirm the test works correctly with Hexagon and AArch64.

quic-seaswara · 2026-05-20T22:16:50Z

Hi @quic-seaswara, Check the updated commit? I have removed the duplicate code. Please run the pipeline? I want to confirm the test works correctly with Hexagon and AArch64.

Before you submit the code, you can locally run ninja check-eld on your machine to verify than waiting for us to trigger the runs. Let me know if that would work for you.

deepakshirkem · 2026-05-20T22:49:17Z

Yes, Will work. Thank You ::((

parth-07 · 2026-05-26T14:34:57Z

+RUN: %link %linkopts %t1.o -o %t1.out 2>&1
+RUN: %readelf -S -W -s %t1.out 2>&1 | %filecheck %s
+#END_TEST
+CHECK: .got.plt PROGBITS [[ADDR:0*[1-9a-f][0-9a-f]*]]


Can we have a common test for all architectures instead of duplicating test per architecture?

One way to do this is to define a lit substitution GlobalOffsetTableSection, and then pass that substitution to
FileCheck using -DGlobalOffsetTableSection=%GlobalOffsetTableSection, then this section can be referred in the CHECKs as [[GlobalOffsetTableSection]]

parth-07

We should remove the older tests (such as test/RISCV/standalone/GlobalOffsetTable/GlobalOffsetTable.test) which are redundant/duplicate now.

ELD did not emit _GLOBAL_OFFSET_TABLE_ for x86-64, causing an undefined reference error when object files reference this symbol. Add _GLOBAL_OFFSET_TABLE_ support for x86-64 and refactor the common implementation into GNULDBackend base class: - GNULDBackend::defineGlobalOffsetTableSymbol(): new helper that defines _GLOBAL_OFFSET_TABLE_ with consistent properties across all targets: Type: Object - consistent with ARM ELD and BFD Binding: Local - consistent with ARM ELD and BFD Visibility: Hidden - consistent with ARM ELD and LLD - x86_64LDBackend::initTargetSymbols(): use helper instead of duplicated addSymbol block. - x86_64LDBackend::defineGOTSymbol(): bind symbol to first .got.plt fragment so it points to the GOT base address. - x86_64LDBackend::finalizeScanRelocations(): call defineGOTSymbol() after scan and report an error if .got.plt is discarded but the symbol is referenced, consistent with GNU ld behavior. Refactor ARM, AArch64, Hexagon backends to use the same helper, eliminating duplicated code. Add _GLOBAL_OFFSET_TABLE_ to RISCV backend which was missing it entirely. Move tests from x86_64/standalone/ to Common/standalone/ following the DynamicGOTPLT pattern. Add per-target test variants for ARM, AArch64, Hexagon, and RISCV covering executable, shared library, PIE, and discard error cases. Fixes qualcomm#570. Signed-off-by: deepakshirkem <deepakshirke509@gmail.com>

deepakshirkem · 2026-05-28T17:08:36Z

Hi @quic-seaswara, Any suggestions.

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_GLOBAL_OFFSET_TABLE_ symbol is not emitted for RISCV target #1200

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		@@ -0,0 +1,11 @@
		#----------GlobalOffsetTable.test--------------------- Executable ------#
		#BEGIN_COMMENT

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deepakshirkem commented May 2, 2026

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Fix

Testing

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