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[ELF] Allow KEEP within OVERLAY (#130661)

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When attempting to add KEEP within an OVERLAY description, which the
Linux kernel would like to do for ARCH=arm to avoid dropping the
.vectors sections with '--gc-sections' [1], ld.lld errors with:

  ld.lld: error: ./arch/arm/kernel/vmlinux.lds:37: section pattern is expected
  >>>  __vectors_lma = .; OVERLAY 0xffff0000 : AT(__vectors_lma) { .vectors { KEEP(*(.vectors)) } ...
  >>>                                                                               ^

readOverlaySectionDescription() does not handle all input section
description keywords, despite GNU ld's documentation stating that "The
section definitions within the OVERLAY construct are identical to those
within the general SECTIONS construct, except that no addresses and no
memory regions may be defined for sections within an OVERLAY."

Reuse the existing parsing in readInputSectionDescription(), which
handles KEEP, allowing the Linux kernel's use case to work properly.

[1]: https://lore.kernel.org/20250221125520.14035-1-ceggers@arri.de/
This commit is contained in:
Nathan Chancellor 2025-03-11 19:58:14 +01:00 committed by GitHub
parent 14176d1084
commit 381599f1fe
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2 changed files with 53 additions and 14 deletions
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16
lld/ELF/ScriptParser.cpp
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@ -988,20 +988,8 @@ OutputDesc *ScriptParser::readOverlaySectionDescription() {
ctx.script->createOutputSection(readName(), getCurrentLocation());
osd->osec.inOverlay = true;
expect("{");
while (auto tok = till("}")) {
uint64_t withFlags = 0;
uint64_t withoutFlags = 0;
if (tok == "INPUT_SECTION_FLAGS") {
std::tie(withFlags, withoutFlags) = readInputSectionFlags();
tok = till("");
}
if (tok == "CLASS")
osd->osec.commands.push_back(make<InputSectionDescription>(
StringRef{}, withFlags, withoutFlags, readSectionClassName()));
else
osd->osec.commands.push_back(
readInputSectionRules(tok, withFlags, withoutFlags));
}
while (auto tok = till("}"))
osd->osec.commands.push_back(readInputSectionDescription(tok));
osd->osec.phdrs = readOutputSectionPhdrs();
return osd;
}

51
lld/test/ELF/linkerscript/overlay-keep.test Normal file
View File

@ -0,0 +1,51 @@
# REQUIRES: x86
# RUN: rm -rf %t && split-file %s %t && cd %t
# RUN: llvm-mc -filetype=obj -triple=x86_64 a.s -o a.o
# RUN: ld.lld a.o --gc-sections --script nokeep.t -o a
# RUN: llvm-objdump --section-headers a | FileCheck --check-prefix=NOKEEP %s
# RUN: ld.lld a.o --gc-sections --script keep.t -o a
# RUN: llvm-objdump --section-headers a | FileCheck --check-prefix=KEEP %s
# NOKEEP: Sections:
# NOKEEP-NEXT: Idx Name Size
# NOKEEP-NEXT: 0 00000000
# NOKEEP-NEXT: 1 .text 00000004
# NOKEEP-NEXT: 2 .keep1 00000000
# KEEP: Sections:
# KEEP-NEXT: Idx Name Size
# KEEP-NEXT: 0 00000000
# KEEP-NEXT: 1 .text 00000004
# KEEP-NEXT: 2 .keep1 00000004
# KEEP-NEXT: 3 .keep2 00000004
#--- a.s
.global _start
_start:
.long 1
.section .keep1, "a"
keep1:
.long 2
.section .keep2, "a"
keep2:
.long 3
#--- nokeep.t
SECTIONS {
.text : { *(.text) }
OVERLAY 0x1000 : AT ( 0x4000 ) {
.keep1 { *(.keep1) }
.keep2 { *(.keep2) }
}
}
#--- keep.t
SECTIONS {
.text : { *(.text) }
OVERLAY 0x1000 : AT ( 0x4000 ) {
.keep1 { KEEP(*(.keep1)) }
.keep2 { KEEP(*(.keep2)) }
}
}