llvm/llvm-projectPublic

NotificationsYou must be signed in to change notification settings
Fork14.5k
Star33.6k

[lld][elf] Skip BP ordering input sections with null data#149265

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to ourterms of service andprivacy statement. We’ll occasionally send you account related emails.

Already on GitHub?Sign in to your account

Jump to bottom

Merged

ellishg merged 2 commits intollvm:mainfromColibrow:colibrow/fix-elf-bss-bp

Jul 18, 2025

Merged

[lld][elf] Skip BP ordering input sections with null data#149265

ellishg merged 2 commits intollvm:mainfromColibrow:colibrow/fix-elf-bss-bp

Jul 18, 2025

Conversation

Copy link

Contributor

Colibrow commentedJul 17, 2025•
edited
Loading

LLD crashes when BP (Balanced Partitioning) ordering is applied to the.bss section, since.bss has a non-zero size but its data pointer is null.

This patch adds a null check for section data in ELF's BPSectionOrderer to avoid crash.

The fix is consistent with the Mach-O implementation in#137906.

llvmbot added lld lld:ELF labels

Jul 17, 2025

Copy link

Member

llvmbot commentedJul 17, 2025•
edited
Loading

@llvm/pr-subscribers-lld-elf

@llvm/pr-subscribers-lld

Author: Pengying Xu (Colibrow)

Changes

Same as#137906.

Full diff:https://github.com/llvm/llvm-project/pull/149265.diff

2 Files Affected:

(modified) lld/ELF/BPSectionOrderer.cpp (+2-2)
(modified) lld/test/ELF/bp-section-orderer.s (+15-6)

diff --git a/lld/ELF/BPSectionOrderer.cpp b/lld/ELF/BPSectionOrderer.cppindex f464b1d4518a4..c471ab163708f 100644--- a/lld/ELF/BPSectionOrderer.cpp+++ b/lld/ELF/BPSectionOrderer.cpp@@ -76,10 +76,10 @@ DenseMap<const InputSectionBase *, int> elf::runBalancedPartitioning(     if (!d)       return;     auto *sec = dyn_cast_or_null<InputSection>(d->section);-    // Skip empty, discarded, ICF folded sections. Skipping ICF folded sections+    // Skip empty, discarded, ICF folded sections, .bss. Skipping ICF folded sections     // reduces duplicate detection work in BPSectionOrderer.     if (!sec || sec->size == 0 || !sec->isLive() || sec->repl != sec ||-        !orderer.secToSym.try_emplace(sec, d).second)+        !orderer.secToSym.try_emplace(sec, d).second || !sec->content().data())       return;     rootSymbolToSectionIdxs[CachedHashStringRef(                                 lld::utils::getRootSymbol(sym.getName()))]diff --git a/lld/test/ELF/bp-section-orderer.s b/lld/test/ELF/bp-section-orderer.sindex 4df2e8d43022e..438d7c2da0f76 100644--- a/lld/test/ELF/bp-section-orderer.s+++ b/lld/test/ELF/bp-section-orderer.s@@ -26,28 +26,28 @@  # RUN: ld.lld -o out.s a.o --irpgo-profile=a.profdata --bp-startup-sort=function # RUN: llvm-nm -jn out.s | tr '\n' , | FileCheck %s --check-prefix=STARTUP-# STARTUP: s5,s4,s3,s2,s1,A,B,C,F,E,D,merged1,merged2,_start,d4,d3,d2,d1,{{$}}+# STARTUP: s5,s4,s3,s2,s1,A,B,C,F,E,D,merged1,merged2,_start,d4,d3,d2,d1,g1,{{$}}  # RUN: ld.lld -o out.os a.o --irpgo-profile=a.profdata --bp-startup-sort=function --symbol-ordering-file a.txt # RUN: llvm-nm -jn out.os | tr '\n' , | FileCheck %s --check-prefix=ORDER-STARTUP-# ORDER-STARTUP: s2,s1,s5,s4,s3,A,F,E,D,B,C,merged1,merged2,_start,d3,d2,d4,d1,{{$}}+# ORDER-STARTUP: s2,s1,s5,s4,s3,A,F,E,D,B,C,merged1,merged2,_start,d3,d2,d4,d1,g1,{{$}}  # RUN: ld.lld -o out.cf a.o --verbose-bp-section-orderer --bp-compression-sort=function 2>&1 | FileCheck %s --check-prefix=BP-COMPRESSION-FUNC # RUN: ld.lld -o out.cf.icf a.o --verbose-bp-section-orderer --bp-compression-sort=function --icf=all --gc-sections 2>&1 | FileCheck %s --check-prefix=BP-COMPRESSION-ICF-FUNC # RUN: llvm-nm -jn out.cf | tr '\n' , | FileCheck %s --check-prefix=CFUNC-# CFUNC: s5,s4,s3,s2,s1,A,F,merged1,merged2,C,E,D,B,_start,d4,d3,d2,d1,{{$}}+# CFUNC: s5,s4,s3,s2,s1,A,F,merged1,merged2,C,E,D,B,_start,d4,d3,d2,d1,g1,{{$}}  # RUN: ld.lld -o out.cd a.o --verbose-bp-section-orderer --bp-compression-sort=data 2>&1 | FileCheck %s --check-prefix=BP-COMPRESSION-DATA # RUN: llvm-nm -jn out.cd | tr '\n' , | FileCheck %s --check-prefix=CDATA-# CDATA: s5,s3,s4,s2,s1,F,C,E,D,B,A,merged1,merged2,_start,d4,d1,d3,d2,{{$}}+# CDATA: s5,s3,s4,s2,s1,F,C,E,D,B,A,merged1,merged2,_start,d4,d1,d3,d2,g1,{{$}}  # RUN: ld.lld -o out.cb a.o --verbose-bp-section-orderer --bp-compression-sort=both 2>&1 | FileCheck %s --check-prefix=BP-COMPRESSION-BOTH # RUN: llvm-nm -jn out.cb | tr '\n' , | FileCheck %s --check-prefix=CBOTH-# CBOTH: s5,s3,s4,s2,s1,A,F,merged1,merged2,C,E,D,B,_start,d4,d1,d3,d2,{{$}}+# CBOTH: s5,s3,s4,s2,s1,A,F,merged1,merged2,C,E,D,B,_start,d4,d1,d3,d2,g1,{{$}}  # RUN: ld.lld -o out.cbs a.o --verbose-bp-section-orderer --bp-compression-sort=both --irpgo-profile=a.profdata --bp-startup-sort=function 2>&1 | FileCheck %s --check-prefix=BP-COMPRESSION-BOTH # RUN: llvm-nm -jn out.cbs | tr '\n' , | FileCheck %s --check-prefix=CBOTH-STARTUP-# CBOTH-STARTUP: s5,s3,s4,s2,s1,A,B,C,F,E,D,merged1,merged2,_start,d4,d1,d3,d2,{{$}}+# CBOTH-STARTUP: s5,s3,s4,s2,s1,A,B,C,F,E,D,merged1,merged2,_start,d4,d1,d3,d2,g1,{{$}}  # BP-COMPRESSION-FUNC: Ordered 9 sections ([[#]] bytes) using balanced partitioning # BP-COMPRESSION-ICF-FUNC: Ordered 8 sections ([[#]] bytes) using balanced partitioning@@ -108,6 +108,7 @@ d3 d2  #--- a.c+int g1; const char s5[] = "engineering"; const char s4[] = "computer program"; const char s3[] = "hardware engineer";@@ -377,6 +378,14 @@ d1: .word6                               // 0x6 .sized1, 16+.typeg1,@object                      // @g1+.section.bss.g1,"aw",@nobits+.globlg1+.p2align2, 0x0+g1:+.word0                               // 0x0+.sizeg1, 4+ .section".note.GNU-stack","",@progbits .addrsig .addrsig_sym F

Copy link

github-actionsbot commentedJul 17, 2025•
edited
Loading

✅ With the latest revision this PR passed the C/C++ code formatter.

[lld][elf] Skip BP ordering input sections with null data

4fba85b

Colibrow force-pushed thecolibrow/fix-elf-bss-bp branch frome7afef3 to4fba85bCompare

July 17, 2025 07:01

Copy link

ContributorAuthor

Colibrow commentedJul 17, 2025

@ellishg @MaskRay Can you take a look at this PR?

ellishg reviewed

Jul 17, 2025

View reviewed changes

lld/ELF/BPSectionOrderer.cpp Outdated

		if (!sec \|\| sec->size == 0 \|\| !sec->isLive() \|\| sec->repl != sec \|\|
		!orderer.secToSym.try_emplace(sec, d).second)
		!orderer.secToSym.try_emplace(sec, d).second \|\| !sec->content().data())

Copy link

Contributor

ellishgJul 17, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others.Learn more.

Why not move the check to before we add the section tosecToSym?

Copy link

ContributorAuthor

ColibrowJul 17, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others.Learn more.

Yeah. Fixed it.

Address comments.

f0944cc

Copy link

Member

MaskRay commentedJul 17, 2025

Same as#137906.

The description is too brief. Does a .bss lead to a crash?

Copy link

ContributorAuthor

Colibrow commentedJul 17, 2025

@MaskRay Yes. I encountered a crash after updating lld to the latest version and enabling BP (Balanced Partitioning) ordering for the .data section in the ELF output.

The ld.lld command returned non-zero exit code: 139.output:PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.Stack dump:0.Program arguments: ld.lld --export ...1.0x00000001025f7432 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (ld.lld+0x101934324)2.0x00000001025f4998 llvm::sys::RunSignalHandlers() (ld.lld+0x101932768)3.0x00000001025f4998 SignalHandler(int) (ld.lld+0x101932768)4.0x0000000193ecfe04 (/usr/lib/system/libsystem_platform.dylib+0x10842e04)5.0x0000000101ac1f1c llvm::SmallVectorBase::unsigned int, 12u>::base::grow_pod(void*, unsigned long, unsigned long) (ld.lld+0x100b6271c)6.0x0000000101e56f14 lld::elf::runBalancedPartitioning(lld::elf::PartitioningParams const&) (ld.lld+0x100eccc14)7.0x0000000101e58204 lld::elf::Ctx::Ctx() (ld.lld+0x100ecde14)8.0x0000000101e5d268 lld::elf::LinkerDriver::LinkerDriver() (ld.lld+0x100ed2c78)9.0x0000000101e5eb74 void lld::elf::writeResult<llvm::object::ELFType<llvm::endianness::little, true>>(lld::elf::Ctx&) (ld.lld+0x100ed4644)10.0x0000000101e5ed3c lld::elf::LinkerDriver::link(llvm::ArrayRef<char const*>) (ld.lld+0x100ed47f4)11.0x0000000101e5ef54 lld::elf::Link(llvm::ArrayRef<char const*>, bool, llvm::raw_ostream&, bool, bool) (ld.lld+0x100ed4a0c)12.0x0000000100003798 lld_main(int, char**, llvm::ToolContext const&) (ld.lld+0x100003798)13.0x0000000100003c98 main (ld.lld+0x100003c98)14.0x000000019fb0274b (/usr/lib/dyld+0x10004274b)

After investigation, I found that the crash occurs inBPSectionOrderer.cpp, where data.data() is nullptr, leading to a segmentation fault.