[lld] 2997441 - [ELF] Support discarding .got.plt

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2021-11-19T10:50:53-08:00
New Revision: 2997441b85c0ec94425e83316d7e63c32d8c5770

URL: https://github.com/llvm/llvm-project/commit/2997441b85c0ec94425e83316d7e63c32d8c5770
DIFF: https://github.com/llvm/llvm-project/commit/2997441b85c0ec94425e83316d7e63c32d8c5770.diff

LOG: [ELF] Support discarding .got.plt

Fix a null pointer dereference when .got.plt is discarded.

This also adds a test for discarding `.plt`.

Reviewed By: ikudrin

Differential Revision: https://reviews.llvm.org/D114180

Added: 
    lld/test/ELF/linkerscript/discard-plt.s

Modified: 
    lld/ELF/SyntheticSections.cpp

Removed: 
    


################################################################################
diff  --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index 1c1720dcbd2a6..f1594eb8df863 100644
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -1668,11 +1668,11 @@ void RelocationBaseSection::finalizeContents() {
   else
     getParent()->link = 0;
 
-  if (in.relaPlt == this) {
+  if (in.relaPlt == this && in.gotPlt->getParent()) {
     getParent()->flags |= ELF::SHF_INFO_LINK;
     getParent()->info = in.gotPlt->getParent()->sectionIndex;
   }
-  if (in.relaIplt == this) {
+  if (in.relaIplt == this && in.igotPlt->getParent()) {
     getParent()->flags |= ELF::SHF_INFO_LINK;
     getParent()->info = in.igotPlt->getParent()->sectionIndex;
   }

diff  --git a/lld/test/ELF/linkerscript/discard-plt.s b/lld/test/ELF/linkerscript/discard-plt.s
new file mode 100644
index 0000000000000..eef04eadd8171
--- /dev/null
+++ b/lld/test/ELF/linkerscript/discard-plt.s
@@ -0,0 +1,37 @@
+# REQUIRES: x86
+# RUN: split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/a.s -o %t/a.o
+
+## Discard .plt, .iplt, and .got.plt
+# RUN: ld.lld -shared -T %t/t %t/a.o -o %t/a
+# RUN: llvm-readelf -S -d %t/a > %t/readelf.txt
+# RUN: FileCheck %s --input-file %t/readelf.txt
+# RUN: FileCheck %s --input-file %t/readelf.txt --check-prefix=NEG
+
+# CHECK:      [Nr] Name      Type     Address  Off      Size   ES Flg Lk Inf Al
+# CHECK:      ] .rela.plt RELA     [[#%x,]] [[#%x,]] 000018 18   A  1   0  8
+
+# CHECK:      (PLTGOT)  0x0
+# CHECK:      (PLTREL)  RELA
+
+# NEG-NOT: ] .plt
+# NEG-NOT: ] .iplt
+# NEG-NOT: ] .got.plt
+
+#--- a.s
+  call foo
+  call ifunc
+
+.type ifunc, @gnu_indirect_function
+.hidden ifunc
+ifunc:
+  ret
+
+.data
+.quad ifunc
+
+#--- t
+SECTIONS {
+  .text : { *(.text) }
+  /DISCARD/ : { *(.plt .iplt .got.plt) }
+}