maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

[llvm-objdump] Exclude __mh_*_header symbols during MachO disassembly 

`__mh_(execute|dylib|dylinker|bundle|preload|object)_header` are special symbols whose values hold the VMA of the Mach header to support introspection. They are attached to the first section in `__TEXT`, even though their addresses are outside `__TEXT`, and they do not refer to code.

It is normally harmless, but when the first section of `__TEXT` has no other symbols, `__mh_*_header` is considered by the disassembler when determing function boundaries. Since `__mh_*_header` refers to an address outside `__TEXT`, the boundary determination fails and disassembly quits.

Since `__TEXT,__text` normally has symbols, this bug is obscured. Experiments placing `__stubs` and `__stub_helper` first exposed the bug, since neither has symbols.

Differential Revision: https://reviews.llvm.org/D101786
This commit is contained in:
Greg McGary 2021-05-02 19:08:02 -07:00
parent 46adccc5cc
commit 5a43901539
2 changed files with 100 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

92
llvm/test/tools/llvm-objdump/MachO/no-text-symbols-disassembly.test Normal file
View File

@ -0,0 +1,92 @@
## Verify that we see dissassembler output even when there are no
## symbols in __TEXT,__text.
# RUN: yaml2obj %s -o %t.o
# RUN: llvm-objdump -d %t.o | FileCheck %s
--- !mach-o
FileHeader:
magic: 0xFEEDFACF
cputype: 0x01000007
cpusubtype: 0x00000003
filetype: 0x00000002
ncmds: 4
sizeofcmds: 544
flags: 0x00000001
reserved: 0x00000000
LoadCommands:
- cmd: LC_SEGMENT_64
cmdsize: 72
segname: __PAGEZERO
vmaddr: 0
vmsize: 4294967296
fileoff: 0
filesize: 0
maxprot: 0
initprot: 0
nsects: 0
flags: 0
- cmd: LC_SEGMENT_64
cmdsize: 152
segname: __TEXT
vmaddr: 4294967296
vmsize: 4096
fileoff: 0
filesize: 4096
maxprot: 5
initprot: 5
nsects: 1
flags: 0
Sections:
- sectname: __text
segname: __TEXT
addr: 0x0000000100000FF7
size: 9
offset: 0x00000FF7
align: 0
reloff: 0x00000000
nreloc: 0
flags: 0x80000400
reserved1: 0x00000000
reserved2: 0x00000000
reserved3: 0x00000000
- cmd: LC_SEGMENT_64
cmdsize: 72
segname: __LINKEDIT
vmaddr: 4294971392
vmsize: 4096
fileoff: 4096
filesize: 64
maxprot: 1
initprot: 1
nsects: 0
flags: 0
- cmd: LC_SYMTAB
cmdsize: 24
symoff: 4096
nsyms: 2
stroff: 4128
strsize: 32
LinkEditData:
NameList:
- n_strx: 2
n_type: 0x03
n_sect: 1
n_desc: 16
n_value: 4294967296
- n_strx: 22
n_type: 0x01
n_sect: 0
n_desc: 0
n_value: 0
StringTable:
- ' '
- __mh_execute_header
- start
- ''
- ''
- ''
- ''
...
CHECK: Disassembly of section __TEXT,__text:

11
llvm/tools/llvm-objdump/llvm-objdump.cpp
View File

@ -1076,10 +1076,15 @@ static void disassembleObject(const Target *TheTarget, const ObjectFile *Obj,
if (Obj->isELF() && getElfSymbolType(Obj, Symbol) == ELF::STT_SECTION)
continue;
// Don't ask a Mach-O STAB symbol for its section unless you know that
// STAB symbol's section field refers to a valid section index. Otherwise
// the symbol may error trying to load a section that does not exist.
if (MachO) {
// __mh_(execute|dylib|dylinker|bundle|preload|object)_header are special
// symbols that support MachO header introspection. They do not bind to
// code locations and are irrelevant for disassembly.
if (NameOrErr->startswith("__mh_") && NameOrErr->endswith("_header"))
continue;
// Don't ask a Mach-O STAB symbol for its section unless you know that
// STAB symbol's section field refers to a valid section index. Otherwise
// the symbol may error trying to load a section that does not exist.
DataRefImpl SymDRI = Symbol.getRawDataRefImpl();
uint8_t NType = (MachO->is64Bit() ?
MachO->getSymbol64TableEntry(SymDRI).n_type: