[lld] [ELF] -r --compress-debug-sections: update addends for .debug_* sections relocated by REL (PR #66804)
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 20 14:48:57 PDT 2023
https://github.com/MaskRay updated https://github.com/llvm/llvm-project/pull/66804
>From f93c401a8e5d9ecf40502c2302e07de96e6c8c4f Mon Sep 17 00:00:00 2001
From: Fangrui Song <i at maskray.me>
Date: Tue, 19 Sep 2023 11:11:42 -0700
Subject: [PATCH] [ELF] -r --compress-debug-sections: update implicit addends
for .rel.debug_* referencing STT_SECTION symbols (#66804)
https://reviews.llvm.org/D48929 updated addends for non-SHF_ALLOC sections
relocated by REL for -r links, but the patch did not update the addends when
--compress-debug-sections={zlib,zstd} is used (#66738).
https://reviews.llvm.org/D116946 handled tombstone values in debug
sections in relocatable links. As a side effect, both
relocateNonAllocForRelocatable (using `sec->relocations`) and
relocatenonNonAlloc (using raw REL/RELA) may run.
Actually, we can adjust the condition in relocatenonAlloc to completely replace
relocateNonAllocForRelocatable. This patch implements this idea and fixes #66738.
As relocateNonAlloc processes the raw relocations like copyRelocations() does,
the condition `if (config->relocatable && type != target.noneRel)` in `copyRelocations`
(commit 08d6a3f1337238a480225d4caf71b8fec10dc8c6, modified by https://reviews.llvm.org/D62052)
can be made specific to SHF_ALLOC sections.
As a side effect, we can now report diagnostics for PC-relative relocations for
-r. This is a less useful diagnostic that is not worth too much code. As
https://github.com/ClangBuiltLinux/linux/issues/1937 has violations, just
suppress the warning for -r. Tested by commit 561b98f9e025363b416f4e89af750d01d1e8c4cc.
---
lld/ELF/InputSection.cpp | 40 ++++++++++-------------
lld/test/ELF/relocatable-section-symbol.s | 12 +++----
2 files changed, 22 insertions(+), 30 deletions(-)
diff --git a/lld/ELF/InputSection.cpp b/lld/ELF/InputSection.cpp
index 3023cbfae4a59e5..413fa3856a1426c 100644
--- a/lld/ELF/InputSection.cpp
+++ b/lld/ELF/InputSection.cpp
@@ -463,7 +463,13 @@ void InputSection::copyRelocations(uint8_t *buf,
if (RelTy::IsRela)
p->r_addend = sym.getVA(addend) - section->getOutputSection()->addr;
- else if (config->relocatable && type != target.noneRel)
+ // For SHF_ALLOC sections relocated by REL, append a relocation to
+ // sec->relocations so that relocateAlloc transitively called by
+ // writeSections will update the implicit addend. Non-SHF_ALLOC sections
+ // utilize relocateNonAlloc to process raw relocations and do not need
+ // this sec->relocations change.
+ else if (config->relocatable && (sec->flags & SHF_ALLOC) &&
+ type != target.noneRel)
sec->addReloc({R_ABS, type, rel.offset, addend, &sym});
} else if (config->emachine == EM_PPC && type == R_PPC_PLTREL24 &&
p->r_addend >= 0x8000 && sec->file->ppc32Got2) {
@@ -954,8 +960,10 @@ void InputSection::relocateNonAlloc(uint8_t *buf, ArrayRef<RelTy> rels) {
}
}
- // For a relocatable link, only tombstone values are applied.
- if (config->relocatable)
+ // For a relocatable link, content relocated by RELA remains unchanged and
+ // we can stop here, while content relocated by REL referencing STT_SECTION
+ // needs updating implicit addends.
+ if (config->relocatable && (RelTy::IsRela || sym.type != STT_SECTION))
continue;
if (expr == R_SIZE) {
@@ -987,30 +995,18 @@ void InputSection::relocateNonAlloc(uint8_t *buf, ArrayRef<RelTy> rels) {
// relocations without any errors and relocate them as if they were at
// address 0. For bug-compatibility, we accept them with warnings. We
// know Steel Bank Common Lisp as of 2018 have this bug.
- warn(msg);
+ //
+ // RELA -r stopped earlier and does not get the warning. Suppress the
+ // warning for REL -r as well
+ // (https://github.com/ClangBuiltLinux/linux/issues/1937).
+ if (RelTy::IsRela || !config->relocatable)
+ warn(msg);
target.relocateNoSym(
bufLoc, type,
SignExtend64<bits>(sym.getVA(addend - offset - outSecOff)));
}
}
-// This is used when '-r' is given.
-// For REL targets, InputSection::copyRelocations() may store artificial
-// relocations aimed to update addends. They are handled in relocateAlloc()
-// for allocatable sections, and this function does the same for
-// non-allocatable sections, such as sections with debug information.
-static void relocateNonAllocForRelocatable(InputSection *sec, uint8_t *buf) {
- const unsigned bits = config->is64 ? 64 : 32;
-
- for (const Relocation &rel : sec->relocs()) {
- // InputSection::copyRelocations() adds only R_ABS relocations.
- assert(rel.expr == R_ABS);
- uint8_t *bufLoc = buf + rel.offset;
- uint64_t targetVA = SignExtend64(rel.sym->getVA(rel.addend), bits);
- target->relocate(bufLoc, rel, targetVA);
- }
-}
-
template <class ELFT>
void InputSectionBase::relocate(uint8_t *buf, uint8_t *bufEnd) {
if ((flags & SHF_EXECINSTR) && LLVM_UNLIKELY(getFile<ELFT>()->splitStack))
@@ -1022,8 +1018,6 @@ void InputSectionBase::relocate(uint8_t *buf, uint8_t *bufEnd) {
}
auto *sec = cast<InputSection>(this);
- if (config->relocatable)
- relocateNonAllocForRelocatable(sec, buf);
// For a relocatable link, also call relocateNonAlloc() to rewrite applicable
// locations with tombstone values.
const RelsOrRelas<ELFT> rels = sec->template relsOrRelas<ELFT>();
diff --git a/lld/test/ELF/relocatable-section-symbol.s b/lld/test/ELF/relocatable-section-symbol.s
index 9d8892236304b22..2ee1e7692cf2c59 100644
--- a/lld/test/ELF/relocatable-section-symbol.s
+++ b/lld/test/ELF/relocatable-section-symbol.s
@@ -30,10 +30,11 @@
# RUN: llvm-mc -filetype=obj -triple=i686 %s -o %t1.o
# RUN: ld.lld -r -o %t1 %t1.o %t1.o
-# RUN: llvm-readelf -r -x .data -x .bar -x .debug_line %t1 | FileCheck %s --check-prefixes=REL,REL0
+# RUN: llvm-readelf -r -x .data -x .bar -x .debug_line %t1 | FileCheck %s --check-prefix=REL
+## https://github.com/llvm/llvm-project/issues/66738 Update implicit addends for -r and --compress-debug-sections
# RUN: ld.lld -r --compress-debug-sections=zlib -o %t1.zlib %t1.o %t1.o
# RUN: llvm-objcopy --decompress-debug-sections %t1.zlib %t1.zlib.de
-# RUN: llvm-readelf -r -x .data -x .bar -x .debug_line %t1.zlib.de | FileCheck %s --check-prefixes=REL,REL1
+# RUN: llvm-readelf -r -x .data -x .bar -x .debug_line %t1.zlib.de | FileCheck %s --check-prefix=REL
# REL: Offset Info Type Sym. Value Symbol's Name
# REL-NEXT: 00000000 {{.*}} R_386_32 00000000 .text
@@ -55,11 +56,8 @@
# REL-NEXT: 0x00000000 01000000 05000000 ........
# REL: Hex dump of section '.bar':
# REL-NEXT: 0x00000000 01000000 00000000 02000000 04000000 ................
-# REL0: Hex dump of section '.debug_line':
-# REL0-NEXT: 0x00000000 01000000 00000000 02000000 04000000 ................
-## FIXME: https://github.com/llvm/llvm-project/issues/66738 The implicit addends for the second input section are wrong.
-# REL1: Hex dump of section '.debug_line':
-# REL1-NEXT: 0x00000000 01000000 00000000 01000000 00000000 ................
+# REL: Hex dump of section '.debug_line':
+# REL-NEXT: 0x00000000 01000000 00000000 02000000 04000000 ................
.long 42
.data
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