[lld] [LLD][ELF] Don't spill to same memory region (PR #129795)
Daniel Thornburgh via llvm-commits
llvm-commits at lists.llvm.org
Wed Mar 5 16:35:19 PST 2025
https://github.com/mysterymath updated https://github.com/llvm/llvm-project/pull/129795
>From f7e8896a170eaca14d30f0c66161e0151ef378f9 Mon Sep 17 00:00:00 2001
From: Daniel Thornburgh <dthorn at google.com>
Date: Tue, 4 Mar 2025 11:46:19 -0800
Subject: [PATCH 1/2] [LLD][ELF] Don't spill to same memory region
This prevents spills to the same memory region from causing spilling to
take too many passes to converge.
Handling this at spilling time allows us to relax the generation of
spill sections; specifically, multiple spills can now be generated per
output section. This should be fairly benign, and it would eventually
allow allow linker scripts to express things like holes or minimum
addresses for parts of output sections. The linker could then spill
within an output section whenever address constraints are violated.
---
lld/ELF/LinkerScript.cpp | 31 +++++++++----
lld/test/ELF/linkerscript/section-class.test | 48 ++++++++++++++++++++
2 files changed, 70 insertions(+), 9 deletions(-)
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 120f5271cf229..07f5ad974f754 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -563,7 +563,7 @@ LinkerScript::computeInputSections(const InputSectionDescription *cmd,
continue;
if (!cmd->matchesFile(*sec->file) || pat.excludesFile(*sec->file) ||
- sec->parent == &outCmd || !flagsMatch(sec))
+ !flagsMatch(sec))
continue;
if (sec->parent) {
@@ -626,7 +626,7 @@ LinkerScript::computeInputSections(const InputSectionDescription *cmd,
for (InputSectionDescription *isd : scd->sc.commands) {
for (InputSectionBase *sec : isd->sectionBases) {
- if (sec->parent == &outCmd || !flagsMatch(sec))
+ if (!flagsMatch(sec))
continue;
bool isSpill = sec->parent && isa<OutputSection>(sec->parent);
if (!sec->parent || (isSpill && outCmd.name == "/DISCARD/")) {
@@ -1585,16 +1585,29 @@ bool LinkerScript::spillSections() {
if (isa<PotentialSpillSection>(isec))
continue;
- // Find the next potential spill location and remove it from the list.
auto it = potentialSpillLists.find(isec);
if (it == potentialSpillLists.end())
- continue;
+ break;
+
+ // Consume spills until finding one that might help, then consume it.
PotentialSpillList &list = it->second;
- PotentialSpillSection *spill = list.head;
- if (spill->next)
- list.head = spill->next;
- else
- potentialSpillLists.erase(isec);
+ PotentialSpillSection *spill;
+ for (spill = list.head; spill; spill = spill->next) {
+ if (list.head->next)
+ list.head = spill->next;
+ else
+ potentialSpillLists.erase(isec);
+
+ // Spills to the same regions cannot help.
+ if (spill->getParent()->memRegion == osec->memRegion &&
+ spill->getParent()->lmaRegion == osec->lmaRegion)
+ continue;
+
+ // This spill might resolve the overflow.
+ break;
+ }
+ if (!spill)
+ continue;
// Replace the next spill location with the spilled section and adjust
// its properties to match the new location. Note that the alignment of
diff --git a/lld/test/ELF/linkerscript/section-class.test b/lld/test/ELF/linkerscript/section-class.test
index 5c30b6343653e..0938fe32de81a 100644
--- a/lld/test/ELF/linkerscript/section-class.test
+++ b/lld/test/ELF/linkerscript/section-class.test
@@ -450,3 +450,51 @@ SECTIONS {
# TO-DISCARD: error: section '.two_byte_section' cannot spill from/to /DISCARD/
# TO-DISCARD-WARN: warning: section '.two_byte_section' cannot spill from/to /DISCARD/
+
+#--- same-mem-region.lds
+## Spills to the same memory region do not consume address assignment passes.
+MEMORY {
+ a : ORIGIN = 0, LENGTH = 0
+ b : ORIGIN = 0, LENGTH = 3
+}
+SECTIONS {
+ CLASS(class) { *(.one_byte_section .two_byte_section) }
+ .a00 : { CLASS(class) } >a
+ .a01 : { CLASS(class) } >a
+ .a02 : { CLASS(class) } >a
+ .a03 : { CLASS(class) } >a
+ .a04 : { CLASS(class) } >a
+ .a05 : { CLASS(class) } >a
+ .a06 : { CLASS(class) } >a
+ .a07 : { CLASS(class) } >a
+ .a08 : { CLASS(class) } >a
+ .a09 : { CLASS(class) } >a
+ .a10 : { CLASS(class) } >a
+ .a11 : { CLASS(class) } >a
+ .a12 : { CLASS(class) } >a
+ .a13 : { CLASS(class) } >a
+ .a14 : { CLASS(class) } >a
+ .a15 : { CLASS(class) } >a
+ .a16 : { CLASS(class) } >a
+ .a17 : { CLASS(class) } >a
+ .a18 : { CLASS(class) } >a
+ .a19 : { CLASS(class) } >a
+ .a20 : { CLASS(class) } >a
+ .a21 : { CLASS(class) } >a
+ .a22 : { CLASS(class) } >a
+ .a23 : { CLASS(class) } >a
+ .a24 : { CLASS(class) } >a
+ .a25 : { CLASS(class) } >a
+ .a26 : { CLASS(class) } >a
+ .a27 : { CLASS(class) } >a
+ .a28 : { CLASS(class) } >a
+ .a29 : { CLASS(class) } >a
+ .a30 : { CLASS(class) } >a
+ .b : { CLASS(class) } >b
+}
+
+# RUN: ld.lld -T same-mem-region.lds -o same-mem-region spill.o
+# RUN: llvm-readelf -S same-mem-region | FileCheck %s --check-prefix=SAME-MEM-REGION
+
+# SAME-MEM-REGION: Name Type Address Off Size
+# SAME-MEM-REGION: .b PROGBITS 0000000000000000 001000 000003
>From b1ddf300cd545adb54589f31bed6da580693b01a Mon Sep 17 00:00:00 2001
From: Daniel Thornburgh <dthorn at google.com>
Date: Wed, 5 Mar 2025 16:35:06 -0800
Subject: [PATCH 2/2] Test VMA vs LMA; add fix
---
lld/ELF/LinkerScript.cpp | 7 +-
lld/test/ELF/linkerscript/section-class.test | 118 +++++++++++++------
2 files changed, 90 insertions(+), 35 deletions(-)
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 07f5ad974f754..45c03965d9601 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -1598,8 +1598,11 @@ bool LinkerScript::spillSections() {
else
potentialSpillLists.erase(isec);
- // Spills to the same regions cannot help.
- if (spill->getParent()->memRegion == osec->memRegion &&
+ // Spills to the same region that overflowed cannot help.
+ if (hasRegionOverflowed(osec->memRegion) &&
+ spill->getParent()->memRegion == osec->memRegion)
+ continue;
+ if (hasRegionOverflowed(osec->lmaRegion) &&
spill->getParent()->lmaRegion == osec->lmaRegion)
continue;
diff --git a/lld/test/ELF/linkerscript/section-class.test b/lld/test/ELF/linkerscript/section-class.test
index 0938fe32de81a..5238076439e1b 100644
--- a/lld/test/ELF/linkerscript/section-class.test
+++ b/lld/test/ELF/linkerscript/section-class.test
@@ -452,45 +452,47 @@ SECTIONS {
# TO-DISCARD-WARN: warning: section '.two_byte_section' cannot spill from/to /DISCARD/
#--- same-mem-region.lds
-## Spills to the same memory region do not consume address assignment passes.
+## Spills to the same memory region that overflowed do not consume address assignment passes.
MEMORY {
a : ORIGIN = 0, LENGTH = 0
b : ORIGIN = 0, LENGTH = 3
+ c : ORIGIN = 3, LENGTH = 3
+ d : ORIGIN = 6, LENGTH = 3
}
SECTIONS {
CLASS(class) { *(.one_byte_section .two_byte_section) }
- .a00 : { CLASS(class) } >a
- .a01 : { CLASS(class) } >a
- .a02 : { CLASS(class) } >a
- .a03 : { CLASS(class) } >a
- .a04 : { CLASS(class) } >a
- .a05 : { CLASS(class) } >a
- .a06 : { CLASS(class) } >a
- .a07 : { CLASS(class) } >a
- .a08 : { CLASS(class) } >a
- .a09 : { CLASS(class) } >a
- .a10 : { CLASS(class) } >a
- .a11 : { CLASS(class) } >a
- .a12 : { CLASS(class) } >a
- .a13 : { CLASS(class) } >a
- .a14 : { CLASS(class) } >a
- .a15 : { CLASS(class) } >a
- .a16 : { CLASS(class) } >a
- .a17 : { CLASS(class) } >a
- .a18 : { CLASS(class) } >a
- .a19 : { CLASS(class) } >a
- .a20 : { CLASS(class) } >a
- .a21 : { CLASS(class) } >a
- .a22 : { CLASS(class) } >a
- .a23 : { CLASS(class) } >a
- .a24 : { CLASS(class) } >a
- .a25 : { CLASS(class) } >a
- .a26 : { CLASS(class) } >a
- .a27 : { CLASS(class) } >a
- .a28 : { CLASS(class) } >a
- .a29 : { CLASS(class) } >a
- .a30 : { CLASS(class) } >a
- .b : { CLASS(class) } >b
+ .a00 : { CLASS(class) } >a AT>c
+ .a01 : { CLASS(class) } >a AT>d
+ .a02 : { CLASS(class) } >a AT>d
+ .a03 : { CLASS(class) } >a AT>d
+ .a04 : { CLASS(class) } >a AT>d
+ .a05 : { CLASS(class) } >a AT>d
+ .a06 : { CLASS(class) } >a AT>d
+ .a07 : { CLASS(class) } >a AT>d
+ .a08 : { CLASS(class) } >a AT>d
+ .a09 : { CLASS(class) } >a AT>d
+ .a10 : { CLASS(class) } >a AT>d
+ .a11 : { CLASS(class) } >a AT>d
+ .a12 : { CLASS(class) } >a AT>d
+ .a13 : { CLASS(class) } >a AT>d
+ .a14 : { CLASS(class) } >a AT>d
+ .a15 : { CLASS(class) } >a AT>d
+ .a16 : { CLASS(class) } >a AT>d
+ .a17 : { CLASS(class) } >a AT>d
+ .a18 : { CLASS(class) } >a AT>d
+ .a19 : { CLASS(class) } >a AT>d
+ .a20 : { CLASS(class) } >a AT>d
+ .a21 : { CLASS(class) } >a AT>d
+ .a22 : { CLASS(class) } >a AT>d
+ .a23 : { CLASS(class) } >a AT>d
+ .a24 : { CLASS(class) } >a AT>d
+ .a25 : { CLASS(class) } >a AT>d
+ .a26 : { CLASS(class) } >a AT>d
+ .a27 : { CLASS(class) } >a AT>d
+ .a28 : { CLASS(class) } >a AT>d
+ .a29 : { CLASS(class) } >a AT>d
+ .a30 : { CLASS(class) } >a AT>d
+ .b : { CLASS(class) } >b AT>d
}
# RUN: ld.lld -T same-mem-region.lds -o same-mem-region spill.o
@@ -498,3 +500,53 @@ SECTIONS {
# SAME-MEM-REGION: Name Type Address Off Size
# SAME-MEM-REGION: .b PROGBITS 0000000000000000 001000 000003
+
+#--- same-lma-region.lds
+## Spills to the same load region that overflowed do not consume address assignment passes.
+MEMORY {
+ a : ORIGIN = 0, LENGTH = 0
+ b : ORIGIN = 0, LENGTH = 3
+ c : ORIGIN = 3, LENGTH = 3
+ d : ORIGIN = 6, LENGTH = 3
+}
+SECTIONS {
+ CLASS(class) { *(.one_byte_section .two_byte_section) }
+ .a00 : { CLASS(class) } >c AT>a
+ .a01 : { CLASS(class) } >c AT>a
+ .a02 : { CLASS(class) } >c AT>a
+ .a03 : { CLASS(class) } >c AT>a
+ .a04 : { CLASS(class) } >c AT>a
+ .a05 : { CLASS(class) } >c AT>a
+ .a06 : { CLASS(class) } >c AT>a
+ .a07 : { CLASS(class) } >c AT>a
+ .a08 : { CLASS(class) } >c AT>a
+ .a09 : { CLASS(class) } >c AT>a
+ .a10 : { CLASS(class) } >c AT>a
+ .a11 : { CLASS(class) } >c AT>a
+ .a12 : { CLASS(class) } >c AT>a
+ .a13 : { CLASS(class) } >c AT>a
+ .a14 : { CLASS(class) } >c AT>a
+ .a15 : { CLASS(class) } >c AT>a
+ .a16 : { CLASS(class) } >c AT>a
+ .a17 : { CLASS(class) } >c AT>a
+ .a18 : { CLASS(class) } >c AT>a
+ .a19 : { CLASS(class) } >c AT>a
+ .a20 : { CLASS(class) } >c AT>a
+ .a21 : { CLASS(class) } >c AT>a
+ .a22 : { CLASS(class) } >c AT>a
+ .a23 : { CLASS(class) } >c AT>a
+ .a24 : { CLASS(class) } >c AT>a
+ .a25 : { CLASS(class) } >c AT>a
+ .a26 : { CLASS(class) } >c AT>a
+ .a27 : { CLASS(class) } >c AT>a
+ .a28 : { CLASS(class) } >c AT>a
+ .a29 : { CLASS(class) } >c AT>a
+ .a30 : { CLASS(class) } >c AT>a
+ .b : { CLASS(class) } >c AT>b
+}
+
+# RUN: ld.lld -T same-lma-region.lds -o same-lma-region spill.o
+# RUN: llvm-readelf -S same-lma-region | FileCheck %s --check-prefix=SAME-LMA-REGION
+
+# SAME-LMA-REGION: Name Type Address Off Size
+# SAME-LMA-REGION: .b PROGBITS 0000000000000003 001003 000003
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