[lld] [LLD] [COFF] Don't create pseudo relocations for discardable sections (PR #89043)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo created https://github.com/llvm/llvm-project/pull/89043

This extends on the case from 9c970d5ecd6a85188cd2b0a941fcd4d60063ef81; if a section is marked discardable, it won't be mapped into memory at runtime, so there's no point in creating runtime pseudo relocations for such sections.

>From cd4dfcb604a7685f27daec3cfc9fef8fb5e31727 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <martin at martin.st>
Date: Tue, 16 Apr 2024 11:17:57 +0300
Subject: [PATCH] [LLD] [COFF] Don't create pseudo relocations in discardable
 sections

This extends on the case from 9c970d5ecd6a85188cd2b0a941fcd4d60063ef81;
if a section is marked discardable, it won't be mapped into memory
at runtime, so there's no point in creating runtime pseudo
relocations for such sections.
---
 lld/COFF/Writer.cpp              |  4 +++
 lld/test/COFF/autoimport-debug.s | 43 ++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 lld/test/COFF/autoimport-debug.s

diff --git a/lld/COFF/Writer.cpp b/lld/COFF/Writer.cpp
index 7269d156752de8..68993232f09c0b 100644
--- a/lld/COFF/Writer.cpp
+++ b/lld/COFF/Writer.cpp
@@ -2060,6 +2060,10 @@ void Writer::createRuntimePseudoRelocs() {
     auto *sc = dyn_cast<SectionChunk>(c);
     if (!sc || !sc->live)
       continue;
+    // Don't create pseudo relocations for sections that won't be
+    // mapped at runtime.
+    if (sc->header->Characteristics & IMAGE_SCN_MEM_DISCARDABLE)
+      continue;
     sc->getRuntimePseudoRelocs(rels);
   }
 
diff --git a/lld/test/COFF/autoimport-debug.s b/lld/test/COFF/autoimport-debug.s
new file mode 100644
index 00000000000000..1f31a2b9e554ff
--- /dev/null
+++ b/lld/test/COFF/autoimport-debug.s
@@ -0,0 +1,43 @@
+# REQUIRES: x86
+# RUN: split-file %s %t.dir
+
+## We've got references to variable both in a .refptr and in .debug_info.
+## The .debug_info section should be discardable, so no pseudo relocations
+## need to be created in it. The .refptr section should be elimiated
+## and redirected to __imp_variable instead, so we shouldn't need to
+## create any runtime pseudo relocations. Thus, test that we can link
+## successfully with -runtime-pseudo-reloc:no, while keeping the
+## debug info.
+
+# RUN: llvm-mc -triple=x86_64-windows-gnu %t.dir/lib.s -filetype=obj -o %t.dir/lib.obj
+# RUN: lld-link -out:%t.dir/lib.dll -dll -entry:DllMainCRTStartup %t.dir/lib.obj -lldmingw -implib:%t.dir/lib.lib
+
+# RUN: llvm-mc -triple=x86_64-windows-gnu %t.dir/main.s -filetype=obj -o %t.dir/main.obj
+# RUN: lld-link -lldmingw -out:%t.dir/main.exe -entry:main %t.dir/main.obj %t.dir/lib.lib -opt:noref -debug:dwarf -runtime-pseudo-reloc:no
+
+#--- main.s
+    .global main
+    .text
+main:
+    movq .refptr.variable(%rip), %rax
+    ret
+
+    .section .rdata$.refptr.variable,"dr",discard,.refptr.variable
+    .global .refptr.variable
+.refptr.variable:
+    .quad   variable
+
+    .section .debug_info
+    .long 1
+    .quad variable
+    .long 2
+
+#--- lib.s
+    .global variable
+    .global DllMainCRTStartup
+    .text
+DllMainCRTStartup:
+    ret
+    .data
+variable:
+    .long 42