[llvm] 5899278 - [llvm-objcopy] Exclude empty sections in IHexWriter output
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Sat Jun 12 12:23:17 PDT 2021
Author: Ian McIntyre
Date: 2021-06-12T12:23:07-07:00
New Revision: 5899278758b66a5e72c1ae9695651c2aef7406c4
URL: https://github.com/llvm/llvm-project/commit/5899278758b66a5e72c1ae9695651c2aef7406c4
DIFF: https://github.com/llvm/llvm-project/commit/5899278758b66a5e72c1ae9695651c2aef7406c4.diff
LOG: [llvm-objcopy] Exclude empty sections in IHexWriter output
IHexWriter was evaluating a section's physical address when deciding if
that section should be written to an output. This approach does not
account for a zero-sized section that has the same physical address as a
sized section. The behavior varies from GNU objcopy, and may result in a
HEX file that does not include all program sections.
The IHexWriter now excludes zero-sized sections when deciding what
should be written to the output. This affects the contents of the
writer's `Sections` collection; we will not try to insert multiple
sections that could have the same physical address. The behavior seems
consistent with GNU objcopy, which always excludes empty sections,
no matter the address.
The new test case evaluates the IHexWriter behavior when provided a
variety of empty sections that overlap or append a filled section. See
the input file's comments for more information. Given that test input,
and the change to the IHexWriter, GNU objcopy and llvm-objcopy produce
the same output.
Reviewed By: jhenderson, MaskRay, evgeny777
Differential Revision: https://reviews.llvm.org/D101332
Added:
llvm/test/tools/llvm-objcopy/ELF/ihex-writer-empty-sections.test
Modified:
llvm/test/tools/llvm-objcopy/ELF/Inputs/ihex-elf-sections2.yaml
llvm/tools/llvm-objcopy/ELF/Object.cpp
Removed:
################################################################################
diff --git a/llvm/test/tools/llvm-objcopy/ELF/Inputs/ihex-elf-sections2.yaml b/llvm/test/tools/llvm-objcopy/ELF/Inputs/ihex-elf-sections2.yaml
index 224340cbcc92e..9452e64babe95 100644
--- a/llvm/test/tools/llvm-objcopy/ELF/Inputs/ihex-elf-sections2.yaml
+++ b/llvm/test/tools/llvm-objcopy/ELF/Inputs/ihex-elf-sections2.yaml
@@ -5,15 +5,6 @@ FileHeader:
Type: ET_EXEC
Machine: EM_X86_64
Sections:
- - Name: .text
-# Zero length sections are not exported to IHex
-# 'SegmentAddr' and 'ExtendedAddr' records aren't
-# created either.
- Type: SHT_PROGBITS
- Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
- Address: 0x7FFFFFFF
- AddressAlign: 0x8
- Size: 0
- Name: .text1
# Section address is sign-extended 32-bit address
# Data fits 32-bit range
diff --git a/llvm/test/tools/llvm-objcopy/ELF/ihex-writer-empty-sections.test b/llvm/test/tools/llvm-objcopy/ELF/ihex-writer-empty-sections.test
new file mode 100644
index 0000000000000..d961fe7453a0a
--- /dev/null
+++ b/llvm/test/tools/llvm-objcopy/ELF/ihex-writer-empty-sections.test
@@ -0,0 +1,186 @@
+## Evaluates the hex writer behavior with empty sections and segments.
+##
+## Show that the presence of an empty section placed at the same address of a
+## filled section doesn't affect the hex output. Also, show that the presence of
+## an empty section placed behind the filled section doesn't affect the hex
+## output. And, show that this happens regardless of the section ordering in the
+## section header table. (Two filled sections, and four empty sections, to
+## realize this test.)
+##
+## Then, show the same kind of behaviors for segments. (One filled section, four
+## empty sections, each in a single segment.)
+
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-objcopy -O ihex %t - | FileCheck %s --implicit-check-not={{.}}
+
+## .data0 address
+# CHECK: :02000004333394
+## .data0 offset, contents, checksum
+# CHECK-NEXT: :020000000123DA
+
+## .data1 address
+# CHECK-NEXT: :02000004444472
+## .data1 offset, contents, checksum
+# CHECK-NEXT: :02000000456752
+
+## .data2 address
+# CHECK-NEXT: :0200000477770C
+## .data2 offset, contents, checksum
+# CHECK-NEXT: :0200000089ABCA
+
+## End of file
+# CHECK-NEXT: :00000001FF
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS32
+ Data: ELFDATA2LSB
+ Type: ET_EXEC
+ Machine: EM_ARM
+Sections:
+## An empty section that's placed at the same address as a populated section.
+## This won't be in the output. It also won't affect how the subsequent section
+## is written.
+ - Name: .empty_at_data0
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x33330000
+ Size: 0
+## A section populated with data. This is in the output.
+ - Name: .data0
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x33330000
+ Content: "0123"
+## An empty section that's placed at the end of .data0. This won't be in the
+## output.
+ - Name: .empty_behind_data0
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x33330002
+ Size: 0
+## An empty section declared before .data1, but placed behind .data1. This
+## won't be in the output.
+ - Name: .empty_behind_data1
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x44440002
+ Size: 0
+## A section populated with data. This is in the output.
+ - Name: .data1
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x44440000
+ Content: "4567"
+## An empty section declared after .data1, but placed at the start of .data1.
+## This won't be in the output.
+ - Name: .empty_at_data1
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x44440000
+ Size: 0
+## An empty section that's isolated (by address) from all others. This won't be
+## in the output.
+ - Name: .empty_isolated
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x7FFFFFFF
+ AddressAlign: 0x1
+ Size: 0
+## The sections below are placed into segments of varying configurations.
+## Populated section in its own segment. This is in the output.
+ - Name: .data2
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x77770000
+ Content: "89AB"
+## Empty section in its own segment. That segment is declared before the .data2
+## segment in the program headers, and placed at an address just behind .data2.
+## This won't be in the output.
+ - Name: .empty0
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x88880000
+ Size: 0
+## Empty section in its own segment. That segment is declared before the .data2
+## segment in the program headers, and placed at the same address as .data2.
+## This won't be in the output.
+ - Name: .empty1
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x99990000
+ Size: 0
+## Empty section in its own segment. That segment is declared after the .data2
+## segment in the program headers, and placed at the same address as .data2.
+## This won't be in the output.
+ - Name: .empty2
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0xAAAA0000
+ Size: 0
+## Empty section in its own segment. That segment is declared after the .data2
+## segment in the program headers, and placed at an address just behind .data2.
+## This won't be in the output.
+ - Name: .empty3
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0xBBBB0000
+ Size: 0
+ProgramHeaders:
+## .data0 sections, with empty bookends.
+ - Type: PT_LOAD
+ Flags: [ PF_R ]
+ PAddr: 0x33330000
+ VAddr: 0x33330000
+ FirstSec: .empty_at_data0
+ LastSec: .empty_behind_data0
+## .data1 sections, with empty bookends.
+ - Type: PT_LOAD
+ Flags: [ PF_R ]
+ PAddr: 0x44440000
+ VAddr: 0x44440000
+ FirstSec: .empty_behind_data1
+ LastSec: .empty_at_data1
+## .empty_isolated section.
+ - Type: PT_LOAD
+ Flags: [ PF_R ]
+ PAddr: 0x7FFFFFFF
+ VAddr: 0x7FFFFFFF
+ FirstSec: .empty_isolated
+ LastSec: .empty_isolated
+## Segments below include a single empty segment, and are positioned around
+## .data2 in various ways. Declared before, placed behind .data2 segment.
+ - Type: PT_LOAD
+ Flags: [ PF_R ]
+ PAddr: 0x77770002
+ VAddr: 0x77770002
+ FirstSec: .empty0
+ LastSec: .empty0
+## Declared before, placed at .data2 segment.
+ - Type: PT_LOAD
+ Flags: [ PF_R ]
+ PAddr: 0x77770000
+ VAddr: 0x77770000
+ FirstSec: .empty1
+ LastSec: .empty1
+## Segment for .data2.
+ - Type: PT_LOAD
+ Flags: [ PF_R ]
+ PAddr: 0x77770000
+ VAddr: 0x77770000
+ FirstSec: .data2
+ LastSec: .data2
+## Declared after, placed at .data2 segment.
+ - Type: PT_LOAD
+ Flags: [ PF_R ]
+ PAddr: 0x77770000
+ VAddr: 0x77770000
+ FirstSec: .empty2
+ LastSec: .empty2
+## Declared after, placed behind .data2 segment.
+ - Type: PT_LOAD
+ Flags: [ PF_R ]
+ PAddr: 0x77770002
+ VAddr: 0x77770002
+ FirstSec: .empty3
+ LastSec: .empty3
diff --git a/llvm/tools/llvm-objcopy/ELF/Object.cpp b/llvm/tools/llvm-objcopy/ELF/Object.cpp
index 6764b30c9feb7..4b6028189e0dd 100644
--- a/llvm/tools/llvm-objcopy/ELF/Object.cpp
+++ b/llvm/tools/llvm-objcopy/ELF/Object.cpp
@@ -2668,7 +2668,8 @@ Error IHexWriter::checkSection(const SectionBase &Sec) {
Error IHexWriter::finalize() {
bool UseSegments = false;
auto ShouldWrite = [](const SectionBase &Sec) {
- return (Sec.Flags & ELF::SHF_ALLOC) && (Sec.Type != ELF::SHT_NOBITS);
+ return (Sec.Flags & ELF::SHF_ALLOC) && Sec.Type != ELF::SHT_NOBITS &&
+ Sec.Size > 0;
};
auto IsInPtLoad = [](const SectionBase &Sec) {
return Sec.ParentSegment && Sec.ParentSegment->Type == ELF::PT_LOAD;
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