[PATCH] D60189: [llvm-objcopy] Simplify SHT_NOBITS -> SHT_PROGBITS promotion
Fangrui Song via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Wed Apr 3 03:05:44 PDT 2019
MaskRay created this revision.
MaskRay added reviewers: rupprecht, jhenderson, grimar, jakehehrlich, alexshap.
Herald added subscribers: llvm-commits, arichardson, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.
GNU objcopy uses bfd_elf_get_default_section_type to decide the candidate section type,
which roughly translates to our [a] (I assume SEC_COMMON implies SHF_ALLOC):
(!(Sec.Flags & ELF::SHF_ALLOC) || Flags & (SectionFlag::SecContents | SectionFlag::SecLoad)))
Then, it updates the section type in bfd/elf.c:elf_fake_sections if:
if (this_hdr->sh_type == SHT_NULL)
this_hdr->sh_type = sh_type; // common case
else if (this_hdr->sh_type == SHT_NOBITS
&& sh_type == SHT_PROGBITS
&& (asect->flags & SEC_ALLOC) != 0) // uncommon case
...
this_hdr->sh_type = sh_type;
If the following condition is met the uncommon branch is executed:
if (elf_section_type (osec) == SHT_NULL
&& (osec->flags == isec->flags
|| (final_link
&& ((osec->flags ^ isec->flags)
& ~(SEC_LINK_ONCE | SEC_LINK_DUPLICATES | SEC_RELOC)) == 0)))
I suggest we just ignore this clause and follow the common case
behavior, which is done in this patch. Rationales to do so:
If --set-section-flags is a no-op (osec->flags == isec->flags)
(corresponds to the "readonly" test in set-section-flags.test), GNU
objcopy will require (Sec.Flags & ELF::SHF_ALLOC). [a] is essentially:
Flags & (SectionFlag::SecContents | SectionFlag::SecLoad)
This special case is not really useful. Non-SHF_ALLOC SHT_NOBITS
sections do not make much sense and it doesn't matter if they are
SHT_NOBITS or SHT_PROGBITS.
For all other RUN lines in set-section-flags.test, the new behavior
matches GNU objcopy, i.e. this patch improves compatibility.
Repository:
rL LLVM
https://reviews.llvm.org/D60189
Files:
test/tools/llvm-objcopy/ELF/rename-section-flag.test
test/tools/llvm-objcopy/ELF/set-section-flags.test
tools/llvm-objcopy/ELF/ELFObjcopy.cpp
Index: tools/llvm-objcopy/ELF/ELFObjcopy.cpp
===================================================================
--- tools/llvm-objcopy/ELF/ELFObjcopy.cpp
+++ tools/llvm-objcopy/ELF/ELFObjcopy.cpp
@@ -101,11 +101,10 @@
// Certain flags also promote SHT_NOBITS to SHT_PROGBITS. Don't change other
// section types (RELA, SYMTAB, etc.).
- const SectionFlag NoBitsToProgBitsMask =
- SectionFlag::SecContents | SectionFlag::SecLoad | SectionFlag::SecNoload |
- SectionFlag::SecCode | SectionFlag::SecData | SectionFlag::SecRom |
- SectionFlag::SecDebug;
- if (Sec.Type == SHT_NOBITS && (Flags & NoBitsToProgBitsMask))
+
+ if (Sec.Type == SHT_NOBITS &&
+ (!(Sec.Flags & ELF::SHF_ALLOC) ||
+ Flags & (SectionFlag::SecContents | SectionFlag::SecLoad)))
Sec.Type = SHT_PROGBITS;
}
Index: test/tools/llvm-objcopy/ELF/set-section-flags.test
===================================================================
--- test/tools/llvm-objcopy/ELF/set-section-flags.test
+++ test/tools/llvm-objcopy/ELF/set-section-flags.test
@@ -12,7 +12,7 @@
# RUN: llvm-readobj --sections %t.noload | FileCheck %s --check-prefixes=CHECK,PROGBITS,WRITE
# RUN: llvm-objcopy --set-section-flags=.foo=readonly \
# RUN: --set-section-flags=.baz=readonly --set-section-flags=.rela.baz=readonly %t %t.readonly
-# RUN: llvm-readobj --sections %t.readonly | FileCheck %s --check-prefixes=CHECK,NOBITS
+# RUN: llvm-readobj --sections %t.readonly | FileCheck %s --check-prefixes=CHECK,PROGBITS
# RUN: llvm-objcopy --set-section-flags=.foo=debug \
# RUN: --set-section-flags=.baz=debug --set-section-flags=.rela.baz=debug %t %t.debug
# RUN: llvm-readobj --sections %t.debug | FileCheck %s --check-prefixes=CHECK,PROGBITS,WRITE
@@ -30,13 +30,13 @@
# RUN: llvm-readobj --sections %t.contents | FileCheck %s --check-prefixes=CHECK,PROGBITS,WRITE
# RUN: llvm-objcopy --set-section-flags=.foo=merge \
# RUN: --set-section-flags=.baz=merge --set-section-flags=.rela.baz=merge %t %t.merge
-# RUN: llvm-readobj --sections %t.merge | FileCheck %s --check-prefixes=CHECK,MERGE,NOBITS,WRITE
+# RUN: llvm-readobj --sections %t.merge | FileCheck %s --check-prefixes=CHECK,MERGE,PROGBITS,WRITE
# RUN: llvm-objcopy --set-section-flags=.foo=strings \
# RUN: --set-section-flags=.baz=strings --set-section-flags=.rela.baz=strings %t %t.strings
-# RUN: llvm-readobj --sections %t.strings | FileCheck %s --check-prefixes=CHECK,STRINGS,NOBITS,WRITE
+# RUN: llvm-readobj --sections %t.strings | FileCheck %s --check-prefixes=CHECK,STRINGS,PROGBITS,WRITE
# RUN: llvm-objcopy --set-section-flags=.foo=share \
# RUN: --set-section-flags=.baz=share --set-section-flags=.rela.baz=share %t %t.share
-# RUN: llvm-readobj --sections %t.share | FileCheck %s --check-prefixes=CHECK,NOBITS,WRITE
+# RUN: llvm-readobj --sections %t.share | FileCheck %s --check-prefixes=CHECK,PROGBITS,WRITE
# Multiple flags:
# RUN: llvm-objcopy --set-section-flags=.foo=alloc,readonly,strings \
@@ -46,7 +46,7 @@
# RUN: llvm-objcopy --set-section-flags=.foo=alloc,code \
# RUN: --set-section-flags=.baz=alloc,code \
# RUN: --set-section-flags=.rela.baz=alloc,code %t %t.alloc_code
-# RUN: llvm-readobj --sections %t.alloc_code | FileCheck %s --check-prefixes=CHECK,PROGBITS,ALLOC,EXEC,WRITE
+# RUN: llvm-readobj --sections %t.alloc_code | FileCheck %s --check-prefixes=CHECK,NOBITS,ALLOC,EXEC,WRITE
# Invalid flags:
# RUN: not llvm-objcopy --set-section-flags=.foo=xyzzy %t %t.xyzzy 2>&1 | FileCheck %s --check-prefix=BAD-FLAG
Index: test/tools/llvm-objcopy/ELF/rename-section-flag.test
===================================================================
--- test/tools/llvm-objcopy/ELF/rename-section-flag.test
+++ test/tools/llvm-objcopy/ELF/rename-section-flag.test
@@ -12,7 +12,7 @@
# RUN: llvm-readobj --sections %t.noload | FileCheck %s --check-prefixes=CHECK,PROGBITS,WRITE
# RUN: llvm-objcopy --rename-section=.foo=.bar,readonly \
# RUN: --rename-section=.baz=.blah,readonly %t %t.readonly
-# RUN: llvm-readobj --sections %t.readonly | FileCheck %s --check-prefixes=CHECK,NOBITS
+# RUN: llvm-readobj --sections %t.readonly | FileCheck %s --check-prefixes=CHECK,PROGBITS
# RUN: llvm-objcopy --rename-section=.foo=.bar,debug \
# RUN: --rename-section=.baz=.blah,debug %t %t.debug
# RUN: llvm-readobj --sections %t.debug | FileCheck %s --check-prefixes=CHECK,PROGBITS,WRITE
@@ -30,13 +30,13 @@
# RUN: llvm-readobj --sections %t.contents | FileCheck %s --check-prefixes=CHECK,PROGBITS,WRITE
# RUN: llvm-objcopy --rename-section=.foo=.bar,merge \
# RUN: --rename-section=.baz=.blah,merge %t %t.merge
-# RUN: llvm-readobj --sections %t.merge | FileCheck %s --check-prefixes=CHECK,NOBITS,MERGE,WRITE
+# RUN: llvm-readobj --sections %t.merge | FileCheck %s --check-prefixes=CHECK,PROGBITS,MERGE,WRITE
# RUN: llvm-objcopy --rename-section=.foo=.bar,strings \
# RUN: --rename-section=.baz=.blah,strings %t %t.strings
-# RUN: llvm-readobj --sections %t.strings | FileCheck %s --check-prefixes=CHECK,NOBITS,STRINGS,WRITE
+# RUN: llvm-readobj --sections %t.strings | FileCheck %s --check-prefixes=CHECK,PROGBITS,STRINGS,WRITE
# RUN: llvm-objcopy --rename-section=.foo=.bar,share \
# RUN: --rename-section=.baz=.blah,share %t %t.share
-# RUN: llvm-readobj --sections %t.share | FileCheck %s --check-prefixes=CHECK,NOBITS,WRITE
+# RUN: llvm-readobj --sections %t.share | FileCheck %s --check-prefixes=CHECK,PROGBITS,WRITE
# Multiple flags:
# RUN: llvm-objcopy --rename-section=.foo=.bar,alloc,readonly,strings \
@@ -44,7 +44,7 @@
# RUN: llvm-readobj --sections %t.alloc_ro_strings | FileCheck %s --check-prefixes=CHECK,NOBITS,ALLOC,STRINGS
# RUN: llvm-objcopy --rename-section=.foo=.bar,alloc,code \
# RUN: --rename-section=.baz=.blah,alloc,code %t %t.alloc_code
-# RUN: llvm-readobj --sections %t.alloc_code | FileCheck %s --check-prefixes=CHECK,PROGBITS,ALLOC,EXEC,WRITE
+# RUN: llvm-readobj --sections %t.alloc_code | FileCheck %s --check-prefixes=CHECK,NOBITS,ALLOC,EXEC,WRITE
# Invalid flags:
# RUN: not llvm-objcopy --rename-section=.foo=.bar,xyzzy %t %t.xyzzy 2>&1 | FileCheck %s --check-prefix=BAD-FLAG
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