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[llvm-readobj] - Report a warning when an unexpected DT_SYMENT tag value is met.

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There was a short discussion about this:
https://reviews.llvm.org/D73484#inline-676942

To summarize:
It is a bit unclear to me why the `DT_SYMENT` tag exist.
LLD has the code that does:
"addInt(DT_SYMENT, sizeof(Elf_Sym));" and I guess other linkers has the same logic.
It is unclear why it can be possible to have other values rather than values of
a size of platform symbol. Seems it is not possible, and atm for me it looks that
this tag should not be used. This patch starts reporting the warning when the
value it contains differs from a symbol size for a 32/64 bit platform for safety.
It keeps the rest of the logic we have unchanged. Before this patch we did not handle
the tag at all.

Differential review: https://reviews.llvm.org/D74479
This commit is contained in:
Georgii Rymar 2020-02-12 16:12:09 +03:00
parent 2799d4faca
commit eef8b0bedf
2 changed files with 40 additions and 2 deletions
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32
test/tools/llvm-readobj/ELF/dyn-symbols.test
View File

@ -355,6 +355,9 @@ DynamicSymbols: []
# RUN: yaml2obj %s --docnum=10 -o %t10
# RUN: llvm-readobj --dyn-symbols %t10 2>&1 | FileCheck %s -DFILE=%t10 --check-prefix=DYNSYM-SIZE-INVALID1
# RUN: llvm-readelf --dyn-symbols %t10 2>&1 | FileCheck %s -DFILE=%t10 --check-prefix=DYNSYM-SIZE-INVALID1
# DYNSYM-SIZE-INVALID1: warning: '[[FILE]]': section with index 1 has invalid size (0x1) or entry size (0x10)
## b) The same, but the DT_SYMTAB tag is present. In this case the dynamic tag has priority over the
## information about a location and an entity size of the dynamic symbol table from the section header.
## The code uses sizeof(Elf_Sym) for an entity size, so it can't be incorrect and
@ -363,10 +366,20 @@ DynamicSymbols: []
# RUN: llvm-readobj --dyn-symbols %t11 2>&1 | FileCheck %s -DFILE=%t11 --check-prefix=DYNSYM-SIZE-INVALID2
# RUN: llvm-readelf --dyn-symbols %t11 2>&1 | FileCheck %s -DFILE=%t11 --check-prefix=DYNSYM-SIZE-INVALID2
# DYNSYM-SIZE-INVALID1: warning: '[[FILE]]': section with index 1 has invalid size (0x1) or entry size (0x10)
# DYNSYM-SIZE-INVALID2: warning: '[[FILE]]': section with index 2 has invalid size (0x1){{$}}
## c) In the case when the DT_SYMENT tag is present, we report when it's value does not match the
# value of the symbol size for the platform.
# RUN: yaml2obj %s -D BITS=32 --docnum=12 -o %t12
# RUN: llvm-readobj --dyn-symbols %t12 2>&1 | FileCheck %s -DFILE=%t12 --check-prefix=DYNSYM-SIZE-INVALID3
# RUN: llvm-readelf --dyn-symbols %t12 2>&1 | FileCheck %s -DFILE=%t12 --check-prefix=DYNSYM-SIZE-INVALID3
# RUN: yaml2obj %s -D BITS=64 --docnum=12 -o %t13
# RUN: llvm-readobj --dyn-symbols %t13 2>&1 | FileCheck %s -DFILE=%t13 --check-prefix=DYNSYM-SIZE-INVALID4
# RUN: llvm-readelf --dyn-symbols %t13 2>&1 | FileCheck %s -DFILE=%t13 --check-prefix=DYNSYM-SIZE-INVALID4
# DYNSYM-SIZE-INVALID3: warning: '[[FILE]]': DT_SYMENT value of 0x123 is not the size of a symbol (0x10){{$}}
# DYNSYM-SIZE-INVALID4: warning: '[[FILE]]': DT_SYMENT value of 0x123 is not the size of a symbol (0x18){{$}}
--- !ELF
FileHeader:
Class: ELFCLASS32
@ -401,3 +414,18 @@ ProgramHeaders:
VAddr: 0x100
Sections:
- Section: .dynsym
--- !ELF
FileHeader:
Class: ELFCLASS[[BITS]]
Data: ELFDATA2LSB
Type: ET_DYN
Machine: EM_X86_64
Sections:
- Name: .dynamic
Type: SHT_DYNAMIC
Entries:
- Tag: DT_SYMENT
Value: 0x123
- Tag: DT_NULL
Value: 0

10
tools/llvm-readobj/ELFDumper.cpp
View File

@ -2098,6 +2098,16 @@ void ELFDumper<ELFT>::parseDynamicTable(const ELFFile<ELFT> *Obj) {
}
break;
}
case ELF::DT_SYMENT: {
uint64_t Val = Dyn.getVal();
if (Val != sizeof(Elf_Sym))
reportWarning(createError("DT_SYMENT value of 0x" +
Twine::utohexstr(Val) +
" is not the size of a symbol (0x" +
Twine::utohexstr(sizeof(Elf_Sym)) + ")"),
ObjF->getFileName());
break;
}
case ELF::DT_RELA:
DynRelaRegion.Addr = toMappedAddr(Dyn.getTag(), Dyn.getPtr());
break;