[lld] [ELF] Warn if specified section address is smaller than image base (PR #140187)
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Thu May 15 21:43:56 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-lld-elf
Author: Fangrui Song (MaskRay)
<details>
<summary>Changes</summary>
When -Ttext= or --section-start specifies an address lower than the
image base, this creates a read-only PT_LOAD segment covering the ELF
and program headers but not any sections. This is likely unintentional
and may result in non-ascending PT_LOAD segment p_vaddr values, which
some loaders reject (#<!-- -->138584). Warn and suggest --image-base in this scenario.
---
Full diff: https://github.com/llvm/llvm-project/pull/140187.diff
4 Files Affected:
- (modified) lld/ELF/Writer.cpp (+23-9)
- (modified) lld/test/ELF/linkerscript/out-of-order.s (+12)
- (modified) lld/test/ELF/linkerscript/section-align2.test (+1-1)
- (modified) lld/test/ELF/sectionstart.s (+13-4)
``````````diff
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index 6a0552e808c7b..ea11841731d27 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -1615,17 +1615,31 @@ template <class ELFT> void Writer<ELFT>::finalizeAddressDependentContent() {
sec->addr = 0;
// If addrExpr is set, the address may not be a multiple of the alignment.
- // Warn because this is error-prone.
- for (SectionCommand *cmd : ctx.script->sectionCommands)
- if (auto *osd = dyn_cast<OutputDesc>(cmd)) {
- OutputSection *osec = &osd->osec;
- if (osec->addr % osec->addralign != 0)
- Warn(ctx) << "address (0x" << Twine::utohexstr(osec->addr)
- << ") of section " << osec->name
- << " is not a multiple of alignment (" << osec->addralign
- << ")";
+ // Warn because this is error-prone. In addition, warn if the address
+ // is smaller than the image base when SECTIONS is absent (e.g. when -Ttext
+ // is specified and smaller than the default target image base for no-pie).
+ uint64_t imageBase = ctx.script->hasSectionsCommand || ctx.arg.relocatable
+ ? 0
+ : ctx.target->getImageBase();
+ for (SectionCommand *cmd : ctx.script->sectionCommands) {
+ auto *osd = dyn_cast<OutputDesc>(cmd);
+ if (!osd)
+ continue;
+ OutputSection *osec = &osd->osec;
+ if (osec->addr < imageBase && (osec->flags & SHF_ALLOC)) {
+ Warn(ctx) << "section '" << osec->name << "' address (0x"
+ << Twine::utohexstr(osec->addr)
+ << ") is smaller than image base (0x"
+ << Twine::utohexstr(imageBase) << "); specify --image-base";
}
+ if (osec->addr % osec->addralign != 0)
+ Warn(ctx) << "address (0x" << Twine::utohexstr(osec->addr)
+ << ") of section " << osec->name
+ << " is not a multiple of alignment (" << osec->addralign
+ << ")";
+ }
+
// Sizes are no longer allowed to grow, so all allowable spills have been
// taken. Remove any leftover potential spills.
ctx.script->erasePotentialSpillSections();
diff --git a/lld/test/ELF/linkerscript/out-of-order.s b/lld/test/ELF/linkerscript/out-of-order.s
index 9b834cf712038..2f990e0205f0e 100644
--- a/lld/test/ELF/linkerscript/out-of-order.s
+++ b/lld/test/ELF/linkerscript/out-of-order.s
@@ -31,6 +31,18 @@
# CHECK-NEXT: 5 .hash 00000010 000000000000201c
# CHECK-NEXT: 6 .text 00000008 000000000000202c
+# RUN: ld.lld -e 0 -o %t --script %t.script %t.o --fatal-warnings
+# RUN: llvm-readelf -Sl %t | FileCheck %s --check-prefix=CHECK1
+
+# CHECK1: Name Type Address Off Size ES Flg Lk Inf Al
+# CHECK1-NEXT: NULL 0000000000000000 000000 000000 00 0 0 0
+# CHECK1-NEXT: .text PROGBITS 0000000000000000 001000 000008 00 AX 0 0 4
+# CHECK1-NEXT: .data PROGBITS 0000000000004000 002000 000008 00 WA 0 0 1
+# CHECK1: Program Headers:
+# CHECK1-NEXT: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
+# CHECK1-NEXT: LOAD 0x001000 0x0000000000000000 0x0000000000000000 0x000008 0x000008 R E 0x1000
+# CHECK1-NEXT: LOAD 0x002000 0x0000000000004000 0x0000000000004000 0x000008 0x000008 RW 0x1000
+
.quad 0
.data
.quad 0
diff --git a/lld/test/ELF/linkerscript/section-align2.test b/lld/test/ELF/linkerscript/section-align2.test
index 3eb42cadc059e..3269633b92930 100644
--- a/lld/test/ELF/linkerscript/section-align2.test
+++ b/lld/test/ELF/linkerscript/section-align2.test
@@ -10,7 +10,7 @@
# RUN: llvm-readelf -S %t | FileCheck %s
## Check we don't warn in the absence of SECTIONS.
-# RUN: ld.lld --fatal-warnings -Ttext=0x10000 %t.o -o /dev/null
+# RUN: ld.lld --fatal-warnings -Ttext=0x10000 --image-base=0x10000 %t.o -o /dev/null
# WARN: warning: address (0x10004) of section .data.rel.ro is not a multiple of alignment (16)
# WARN: warning: address (0x20001) of section .data2 is not a multiple of alignment (8)
diff --git a/lld/test/ELF/sectionstart.s b/lld/test/ELF/sectionstart.s
index d694c9375fd80..a1202bc185a70 100644
--- a/lld/test/ELF/sectionstart.s
+++ b/lld/test/ELF/sectionstart.s
@@ -1,9 +1,13 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
# RUN: ld.lld %t.o --section-start .text=0x100000 \
-# RUN: --section-start=.data=0x110000 --section-start .bss=0x200000 -o %t
+# RUN: --section-start=.data=0x110000 --section-start .bss=0x200000 -o %t 2>&1 | \
+# RUN: FileCheck %s --check-prefix=LINK --implicit-check-not=warning:
# RUN: llvm-objdump --section-headers %t | FileCheck %s
+# LINK: warning: section '.text' address (0x100000) is smaller than image base (0x200000); specify --image-base
+# LINK-NEXT: warning: section '.data' address (0x110000) is smaller than image base (0x200000); specify --image-base
+
# CHECK: Sections:
# CHECK-NEXT: Idx Name Size VMA Type
# CHECK-NEXT: 0 00000000 0000000000000000
@@ -11,9 +15,14 @@
# CHECK-NEXT: 2 .data 00000004 0000000000110000 DATA
# CHECK-NEXT: 3 .bss 00000004 0000000000200000 BSS
-## The same, but dropped "0x" prefix.
-# RUN: ld.lld %t.o --section-start .text=100000 \
-# RUN: --section-start .data=110000 --section-start .bss=0x200000 -o %t1
+## The warnings go away when the image base is 0.
+# RUN: ld.lld %t.o -pie --section-start .text=0x100000 \
+# RUN: --section-start=.data=0x110000 --section-start .bss=0x200000 -o %t --noinhibit-exec
+# RUN: llvm-objdump --section-headers %t | FileCheck %s
+
+## The same, but dropped "0x" prefix. Specify a smaller --image-base to suppress warnings.
+# RUN: ld.lld %t.o --image-base=0x90000 --section-start .text=100000 \
+# RUN: --section-start .data=110000 --section-start .bss=0x200000 -o %t1 --noinhibit-exec
# RUN: llvm-objdump --section-headers %t1 | FileCheck %s
## Use -Ttext, -Tdata, -Tbss as replacement for --section-start:
``````````
</details>
https://github.com/llvm/llvm-project/pull/140187
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