[llvm-branch-commits] [llvm] d4d4c6b - [llvm-objcopy] -O binary: skip empty sections
Fangrui Song via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Fri May 1 20:43:24 PDT 2020
Author: Fangrui Song
Date: 2020-05-01T20:42:53-07:00
New Revision: d4d4c6bf834142326301a743d2939e868d9f0f0f
URL: https://github.com/llvm/llvm-project/commit/d4d4c6bf834142326301a743d2939e868d9f0f0f
DIFF: https://github.com/llvm/llvm-project/commit/d4d4c6bf834142326301a743d2939e868d9f0f0f.diff
LOG: [llvm-objcopy] -O binary: skip empty sections
After SHF_ALLOC sections are ordered by LMA:
* If initial sections are empty, GNU objcopy skips their contents while we
emit leading zeros. (binary-paddr.test %t4)
* If trailing sections are empty, GNU objcopy skips their contents while we
emit trailing zeros. (binary-paddr.test %t5)
This patch matches GNU objcopy's behavior. Linkers don't keep p_memsz
PT_LOAD segments. Such empty sections would not have a containing
PT_LOAD and `Section::ParentSegment` might be null if linkers fail to
optimize the file offsets (lld D79254).
In particular, without D79254, the arm Linux kernel's multi_v5_defconfig
depends on this behavior: in `vmlinux`, an empty .text_itcm is mapped at
a very high address (0xfffe0000) but the kernel does not expect
`objcopy -O binary` to create a very large `arch/arm/boot/Image`
(0xfffe0000-0xc0000000 ~= 1GiB). See https://bugs.llvm.org/show_bug.cgi?id=45632
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D79229
(cherry picked from commit ec786906f5feb4dceba1b5338927079e63e78095)
Added:
Modified:
llvm/test/tools/llvm-objcopy/ELF/binary-paddr.test
llvm/tools/llvm-objcopy/ELF/Object.cpp
Removed:
################################################################################
diff --git a/llvm/test/tools/llvm-objcopy/ELF/binary-paddr.test b/llvm/test/tools/llvm-objcopy/ELF/binary-paddr.test
index 5ac692dc5f86..af961422a155 100644
--- a/llvm/test/tools/llvm-objcopy/ELF/binary-paddr.test
+++ b/llvm/test/tools/llvm-objcopy/ELF/binary-paddr.test
@@ -48,7 +48,7 @@ ProgramHeaders:
# RUN: od -A x -t x2 %t2.out | FileCheck %s --check-prefix=CHECK2 --ignore-case
# RUN: wc -c %t2.out | FileCheck %s --check-prefix=SIZE2
-## The computed LMA of .data is 0x4000. The minimum LMA of all sections is 0x1000.
+## The computed LMA of .data is 0x4000. The minimum LMA of all non-empty sections is 0x1000.
## The content of .data will be written at 0x4000-0x1000 = 0x3000.
# CHECK2: 000000 c3c3 c3c3 0000 0000 0000 0000 0000 0000
# CHECK2-NEXT: 000010 0000 0000 0000 0000 0000 0000 0000 0000
@@ -93,7 +93,7 @@ ProgramHeaders:
# RUN: od -A x -t x2 %t3.out | FileCheck %s --check-prefix=CHECK3 --ignore-case
# RUN: wc -c %t3.out | FileCheck %s --check-prefix=SIZE3
-## The minimum LMA of all sections is 0x1000.
+## The minimum LMA of all non-empty sections is 0x1000.
## The content of .data will be written at 0x3000-0x1000 = 0x2000.
# CHECK3: 000000 c3c3 c3c3 0000 0000 0000 0000 0000 0000
# CHECK3-NEXT: 000010 0000 0000 0000 0000 0000 0000 0000 0000
@@ -130,3 +130,58 @@ ProgramHeaders:
PAddr: 0x3000
Sections:
- Section: .data
+
+## The first section (.text) is empty. Test that we skip its LMA until the first
+## non-empty section, otherwise we would leave a large number of leading zeroes.
+# RUN: yaml2obj --docnum=4 %s -o %t4
+# RUN: llvm-objcopy -O binary %t4 %t4.out
+# RUN: od -A x -t x2 %t4.out | FileCheck %s --check-prefix=SKIPEMPTY
+
+# SKIPEMPTY: 000000 3232
+# SKIPEMPTY-NEXT: 000002
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_EXEC
+ Machine: EM_X86_64
+Sections:
+ - Name: .text
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
+ Address: 0x1000
+ AddressAlign: 0x1000
+ - Name: gap
+ Type: Fill
+ Size: 0x1000
+ - Name: .data
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC, SHF_WRITE ]
+ Content: "3232"
+
+## The last section (.data) is empty. Test that we stop dumping after the last
+## non-empty section, otherwise we would leave a large number of trailing zeroes.
+# RUN: yaml2obj --docnum=5 %s -o %t5
+# RUN: llvm-objcopy -O binary %t5 %t5.out
+# RUN: od -A x -t x2 %t5.out | FileCheck %s --check-prefix=SKIPEMPTY
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_EXEC
+ Machine: EM_X86_64
+Sections:
+ - Name: .text
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
+ Address: 0x1000
+ AddressAlign: 0x1000
+ Content: "3232"
+ - Name: gap
+ Type: Fill
+ Size: 0xffd
+ - Name: .data
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC, SHF_WRITE ]
diff --git a/llvm/tools/llvm-objcopy/ELF/Object.cpp b/llvm/tools/llvm-objcopy/ELF/Object.cpp
index ad53c75663ec..98f72959ae55 100644
--- a/llvm/tools/llvm-objcopy/ELF/Object.cpp
+++ b/llvm/tools/llvm-objcopy/ELF/Object.cpp
@@ -2254,25 +2254,26 @@ Error BinaryWriter::finalize() {
OrderedSegments.erase(End, std::end(OrderedSegments));
// Compute the section LMA based on its sh_offset and the containing segment's
- // p_offset and p_paddr. Also compute the minimum LMA of all sections as
- // MinAddr. In the output, the contents between address 0 and MinAddr will be
- // skipped.
+ // p_offset and p_paddr. Also compute the minimum LMA of all non-empty
+ // sections as MinAddr. In the output, the contents between address 0 and
+ // MinAddr will be skipped.
uint64_t MinAddr = UINT64_MAX;
for (SectionBase &Sec : Obj.allocSections()) {
if (Sec.ParentSegment != nullptr)
Sec.Addr =
Sec.Offset - Sec.ParentSegment->Offset + Sec.ParentSegment->PAddr;
- MinAddr = std::min(MinAddr, Sec.Addr);
+ if (Sec.Size > 0)
+ MinAddr = std::min(MinAddr, Sec.Addr);
}
// Now that every section has been laid out we just need to compute the total
// file size. This might not be the same as the offset returned by
// layoutSections, because we want to truncate the last segment to the end of
- // its last section, to match GNU objcopy's behaviour.
+ // its last non-empty section, to match GNU objcopy's behaviour.
TotalSize = 0;
for (SectionBase &Sec : Obj.allocSections()) {
Sec.Offset = Sec.Addr - MinAddr;
- if (Sec.Type != SHT_NOBITS)
+ if (Sec.Type != SHT_NOBITS && Sec.Size > 0)
TotalSize = std::max(TotalSize, Sec.Offset + Sec.Size);
}
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