[lld] [LLD][ELF] Allow memory region in OVERLAY (PR #133540)
Daniel Thornburgh via llvm-commits
llvm-commits at lists.llvm.org
Mon Mar 31 09:56:56 PDT 2025
https://github.com/mysterymath updated https://github.com/llvm/llvm-project/pull/133540
>From 1f8956350cad0f9bc3b851ed18a6411ad2b58a5a Mon Sep 17 00:00:00 2001
From: Daniel Thornburgh <dthorn at google.com>
Date: Tue, 25 Mar 2025 14:41:10 -0700
Subject: [PATCH 1/2] [LLD][ELF] Allow memory region in OVERLAY
This allows the contents of OVERLAYs to be attributed to memory regions.
This is the only clean way to overlap VMAs in linker scripts that choose
to primarily use memory regions to lay out addresses.
This also simplifies OVERLAY expansion to better match GNU LD.
Expressions for the first section's LMA and VMA are not generated if the
user did not provide them. This allows the LMA/VMA offset to be
preserved across multiple overlays in the same region, as with regular
sections.
Fixes #129816
---
lld/ELF/LinkerScript.cpp | 15 +++++++++++-
lld/ELF/LinkerScript.h | 1 +
lld/ELF/OutputSections.h | 1 +
lld/ELF/ScriptParser.cpp | 23 +++++++++--------
lld/test/ELF/linkerscript/overlay.test | 34 ++++++++++++++++++++++++++
5 files changed, 63 insertions(+), 11 deletions(-)
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index e19823f2ea752..8437049a209d9 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -182,7 +182,18 @@ void LinkerScript::expandMemoryRegions(uint64_t size) {
void LinkerScript::expandOutputSection(uint64_t size) {
state->outSec->size += size;
- expandMemoryRegions(size);
+ size_t regionSize = size;
+ if (state->outSec->inOverlay) {
+ // Expand the overlay if necessary, and expand the region by the
+ // corresponding amount.
+ if (state->outSec->size > state->overlaySize) {
+ regionSize = state->outSec->size - state->overlaySize;
+ state->overlaySize = state->outSec->size;
+ } else {
+ regionSize = 0;
+ }
+ }
+ expandMemoryRegions(regionSize);
}
void LinkerScript::setDot(Expr e, const Twine &loc, bool inSec) {
@@ -1273,6 +1284,8 @@ bool LinkerScript::assignOffsets(OutputSection *sec) {
// NOBITS TLS sections are similar. Additionally save the end address.
state->tbssAddr = dot;
dot = savedDot;
+ } else if (sec->lastInOverlay) {
+ state->overlaySize = 0;
}
return addressChanged;
}
diff --git a/lld/ELF/LinkerScript.h b/lld/ELF/LinkerScript.h
index 0a2dda13f4ef8..65c443ba74d27 100644
--- a/lld/ELF/LinkerScript.h
+++ b/lld/ELF/LinkerScript.h
@@ -311,6 +311,7 @@ class LinkerScript final {
MemoryRegion *lmaRegion = nullptr;
uint64_t lmaOffset = 0;
uint64_t tbssAddr = 0;
+ uint64_t overlaySize = 0;
};
Ctx &ctx;
diff --git a/lld/ELF/OutputSections.h b/lld/ELF/OutputSections.h
index 3ab36a21ce488..33516a62ecb43 100644
--- a/lld/ELF/OutputSections.h
+++ b/lld/ELF/OutputSections.h
@@ -102,6 +102,7 @@ class OutputSection final : public SectionBase {
bool expressionsUseSymbols = false;
bool usedInExpression = false;
bool inOverlay = false;
+ bool lastInOverlay = false;
// Tracks whether the section has ever had an input section added to it, even
// if the section was later removed (e.g. because it is a synthetic section
diff --git a/lld/ELF/ScriptParser.cpp b/lld/ELF/ScriptParser.cpp
index 4c52bfda7a70e..09786aebaf337 100644
--- a/lld/ELF/ScriptParser.cpp
+++ b/lld/ELF/ScriptParser.cpp
@@ -561,37 +561,40 @@ void ScriptParser::readSearchDir() {
// https://sourceware.org/binutils/docs/ld/Overlay-Description.html#Overlay-Description
SmallVector<SectionCommand *, 0> ScriptParser::readOverlay() {
Expr addrExpr;
- if (consume(":")) {
- addrExpr = [s = ctx.script] { return s->getDot(); };
- } else {
+ if (!consume(":")) {
addrExpr = readExpr();
expect(":");
}
- // When AT is omitted, LMA should equal VMA. script->getDot() when evaluating
- // lmaExpr will ensure this, even if the start address is specified.
- Expr lmaExpr = consume("AT") ? readParenExpr()
- : [s = ctx.script] { return s->getDot(); };
+ Expr lmaExpr = consume("AT") ? readParenExpr() : Expr{};
expect("{");
SmallVector<SectionCommand *, 0> v;
OutputSection *prev = nullptr;
while (!errCount(ctx) && !consume("}")) {
// VA is the same for all sections. The LMAs are consecutive in memory
- // starting from the base load address specified.
+ // starting from the base load address.
OutputDesc *osd = readOverlaySectionDescription();
osd->osec.addrExpr = addrExpr;
if (prev) {
osd->osec.lmaExpr = [=] { return prev->getLMA() + prev->size; };
} else {
osd->osec.lmaExpr = lmaExpr;
- // Use first section address for subsequent sections as initial addrExpr
- // can be DOT. Ensure the first section, even if empty, is not discarded.
+ // Use first section address for subsequent sections. Ensure the first
+ // section, even if empty, is not discarded.
osd->osec.usedInExpression = true;
addrExpr = [=]() -> ExprValue { return {&osd->osec, false, 0, ""}; };
}
v.push_back(osd);
prev = &osd->osec;
}
+ if (!v.empty())
+ static_cast<OutputDesc *>(v.back())->osec.lastInOverlay = true;
+ if (consume(">")) {
+ StringRef regionName = readName();
+ for (SectionCommand *od : v)
+ static_cast<OutputDesc *>(od)->osec.memoryRegionName =
+ std::string(regionName);
+ }
// According to the specification, at the end of the overlay, the location
// counter should be equal to the overlay base address plus size of the
diff --git a/lld/test/ELF/linkerscript/overlay.test b/lld/test/ELF/linkerscript/overlay.test
index 7c64303b45659..8324c81a57092 100644
--- a/lld/test/ELF/linkerscript/overlay.test
+++ b/lld/test/ELF/linkerscript/overlay.test
@@ -9,6 +9,7 @@
## .text does not cause overlapping error and that
## .text's VA is 0x1000 + max(sizeof(.out.big), sizeof(.out.small)).
+# RUN: ld.lld a.o -T a.t -o a
# RUN: llvm-readelf --sections -l a | FileCheck %s
# CHECK: Name Type Address Off Size
@@ -41,6 +42,23 @@
# ERR2-NEXT:>>> .out.aaa { *(.aaa) } > AX AT>FLASH
# ERR2-NEXT:>>> ^
+# RUN: ld.lld a.o -T region.t -o region
+# RUN: llvm-readelf --sections -l region | FileCheck --check-prefix=REGION %s
+
+# REGION: Name Type Address Off Size
+# REGION: .big1 PROGBITS 0000000000001000 001000 000008
+# REGION-NEXT: .small1 PROGBITS 0000000000001000 002000 000004
+# REGION: .big2 PROGBITS 0000000000001008 002008 000008
+# REGION-NEXT: .small2 PROGBITS 0000000000001008 003008 000004
+# REGION-NEXT: .text PROGBITS 0000000000001010 003010 000001
+
+# REGION: Program Headers:
+# REGION: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
+# REGION-NEXT: LOAD 0x001000 0x0000000000001000 0x0000000000001000 0x000008 0x000008 R 0x1000
+# REGION-NEXT: LOAD 0x002000 0x0000000000001000 0x0000000000001008 0x000010 0x000010 R 0x1000
+# REGION-NEXT: LOAD 0x003008 0x0000000000001008 0x0000000000001018 0x000004 0x000004 R 0x1000
+# REGION-NEXT: LOAD 0x003010 0x0000000000001010 0x0000000000001020 0x000001 0x000001 R E 0x1000
+
#--- a.s
.globl _start
_start:
@@ -76,6 +94,22 @@ SECTIONS {
.text : { *(.text) }
}
+#--- region.t
+MEMORY { region : ORIGIN = 0x1000, LENGTH = 0x1000 }
+SECTIONS {
+## Memory region instead of explicit address.
+ OVERLAY : {
+ .big1 { *(.big1) }
+ .small1 { *(.small1) }
+ } >region
+ OVERLAY : {
+ .big2 { *(.big2) }
+ .small2 { *(.small2) }
+ } >region
+ .text : { *(.text) } >region
+ /DISCARD/ : { *(.big* .small*) }
+}
+
#--- err1.t
SECTIONS {
OVERLAY 0x1000 : AT ( 0x2000 ) {
>From c7293b45b0aa3a6784d64c16e0459184ced6b287 Mon Sep 17 00:00:00 2001
From: Daniel Thornburgh <mysterymath at gmail.com>
Date: Mon, 31 Mar 2025 09:56:45 -0700
Subject: [PATCH 2/2] Remove spurious RUN line
---
lld/test/ELF/linkerscript/overlay.test | 1 -
1 file changed, 1 deletion(-)
diff --git a/lld/test/ELF/linkerscript/overlay.test b/lld/test/ELF/linkerscript/overlay.test
index 8324c81a57092..e230134ad5541 100644
--- a/lld/test/ELF/linkerscript/overlay.test
+++ b/lld/test/ELF/linkerscript/overlay.test
@@ -9,7 +9,6 @@
## .text does not cause overlapping error and that
## .text's VA is 0x1000 + max(sizeof(.out.big), sizeof(.out.small)).
-# RUN: ld.lld a.o -T a.t -o a
# RUN: llvm-readelf --sections -l a | FileCheck %s
# CHECK: Name Type Address Off Size
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