Incorrect CIE version 3 in object files for platforms defaulting to DWARF2

[DimitryAndric]

Bugzilla Link	22046
Version	trunk
OS	All
CC	@emaste,@pogo59

Extended Description

As discussed on the llvm-commits list [1], for platforms which default to emitting DWARF2, such as *BSD, Darwin and Solaris, clang can output an incorrect CIE version field in object files, depending on whether -g is used or not.

This behavior was introduced by r211272. A simple demonstration (as already shown on the mailing list):

$ cat build-config-test.c
int f (void) { return 0; }
$ ~/obj/llvm-r211272/bin/clang -c build-config-test.c -o test-r211272-without-g.o
$ ~/obj/llvm-r211272/bin/clang -c -g build-config-test.c -o test-r211272-with-g.o
$ strip test-r211272-without-g.o
$ strip test-r211272-with-g.o
$ dwarfdump -v -F test-r211272-without-g.o

.eh_frame

fde:
< 0><0x00000020:0x0000002b><><fde offset 0x00000018 length: 0x0000001c><eh aug data len 0x0>
0x00000020:
0x00000021:
0x00000024:

cie:
< 0> version 3
cie section offset 0 0x00000000
augmentation zR
code_alignment_factor 1
data_alignment_factor -8
return_address_register 16
eh aug data len 0x1 bytes 0x1b
bytes of initial instructions 7
cie length 20
initial instructions
0 DW_CFA_def_cfa r7 8
3 DW_CFA_offset r16 -8 (1 * -8)
5 DW_CFA_nop
6 DW_CFA_nop

$ dwarfdump -v -F test-r211272-with-g.o

.eh_frame

fde:
< 0><0x00000020:0x0000002b><><fde offset 0x00000018 length: 0x0000001c><eh aug data len 0x0>
0x00000020:
0x00000021:
0x00000024:

cie:
< 0> version 1
cie section offset 0 0x00000000
augmentation zR
code_alignment_factor 1
data_alignment_factor -8
return_address_register 16
eh aug data len 0x1 bytes 0x1b
bytes of initial instructions 7
cie length 20
initial instructions
0 DW_CFA_def_cfa r7 8
3 DW_CFA_offset r16 -8 (1 * -8)
5 DW_CFA_nop
6 DW_CFA_nop

E.g., without the -g option, the CIE version is incorrectly set to 3, while with the -g option, the CIE version is correctly set to 1.

This still reproduces on trunk r224901, as of 2014-12-28.

[1] http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20141222/250134.html

[DimitryAndric]

*** Bug llvm/llvm-bugzilla-archive#23192 has been marked as a duplicate of this bug. ***

[llvmbot]

Using the test from my report of...

echo "int f (void) { return 0; }" > conftest.c
clang-3.7 -emit-llvm -g -c conftest.c

it see the following walk in lldb...

% lldb /sw/opt/llvm-3.7.0/bin/llc
(lldb) target create "/sw/opt/llvm-3.7.0/bin/llc"
Current executable set to '/sw/opt/llvm-3.7.0/bin/llc' (x86_64).
(lldb) b Module.cpp:460
Breakpoint 1: where = llc`llvm::Module::getDwarfVersion() const + 68 at Module.cpp:460, address = 0x0000000100bd47c4
(lldb) r conftest.bc
Process 47262 launched: '/sw/opt/llvm-3.7.0/bin/llc' (x86_64)
Process 47262 stopped

• thread #​1: tid = 0xe183d1, 0x0000000100bd47c4 llcllvm::Module::getDwarfVersion(this=0x0000000102c0a960) const + 68 at Module.cpp:460, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1 frame #​0: 0x0000000100bd47c4 llcllvm::Module::getDwarfVersion(this=0x0000000102c0a960) const + 68 at Module.cpp:460
  457
  458 unsigned Module::getDwarfVersion() const {
  459 auto *Val = cast_or_null(getModuleFlag("Dwarf Version"));
  -> 460 if (!Val)
  461 return dwarf::DWARF_VERSION;
  462 return cast(Val->getValue())->getZExtValue();
  463 }
  (lldb) s
  Process 47262 stopped
• thread #​1: tid = 0xe183d1, 0x0000000100bd47de llcllvm::Module::getDwarfVersion(this=0x0000000102c0a960) const + 94 at Module.cpp:462, queue = 'com.apple.main-thread', stop reason = step in frame #​0: 0x0000000100bd47de llcllvm::Module::getDwarfVersion(this=0x0000000102c0a960) const + 94 at Module.cpp:462
  459 auto *Val = cast_or_null(getModuleFlag("Dwarf Version"));
  460 if (!Val)
  461 return dwarf::DWARF_VERSION;
  -> 462 return cast(Val->getValue())->getZExtValue();
  463 }
  464
  465 Comdat *Module::getOrInsertComdat(StringRef Name) {

whereas for...

clang-3.7 -emit-llvm -c conftest.c
lldb /sw/opt/llvm-3.7.0/bin/llc
(lldb) target create "/sw/opt/llvm-3.7.0/bin/llc"
Current executable set to '/sw/opt/llvm-3.7.0/bin/llc' (x86_64).
(lldb) b Module.cpp:460
Breakpoint 1: where = llc`llvm::Module::getDwarfVersion() const + 68 at Module.cpp:460, address = 0x0000000100bd47c4
(lldb) r conftest.bc
Process 47413 launched: '/sw/opt/llvm-3.7.0/bin/llc' (x86_64)
Process 47413 stopped

• thread #​1: tid = 0xe18ba1, 0x0000000100bd47c4 llcllvm::Module::getDwarfVersion(this=0x0000000102c0a960) const + 68 at Module.cpp:460, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1 frame #​0: 0x0000000100bd47c4 llcllvm::Module::getDwarfVersion(this=0x0000000102c0a960) const + 68 at Module.cpp:460
  457
  458 unsigned Module::getDwarfVersion() const {
  459 auto *Val = cast_or_null(getModuleFlag("Dwarf Version"));
  -> 460 if (!Val)
  461 return dwarf::DWARF_VERSION;
  462 return cast(Val->getValue())->getZExtValue();
  463 }
  (lldb) s
  Process 47413 stopped
• thread #​1: tid = 0xe18ba1, 0x0000000100bd47d2 llcllvm::Module::getDwarfVersion(this=0x0000000102c0a960) const + 82 at Module.cpp:461, queue = 'com.apple.main-thread', stop reason = step in frame #​0: 0x0000000100bd47d2 llcllvm::Module::getDwarfVersion(this=0x0000000102c0a960) const + 82 at Module.cpp:461
  458 unsigned Module::getDwarfVersion() const {
  459 auto *Val = cast_or_null(getModuleFlag("Dwarf Version"));
  460 if (!Val)
  -> 461 return dwarf::DWARF_VERSION;
  462 return cast(Val->getValue())->getZExtValue();
  463 }
  464
  (lldb) s
  Process 47413 stopped
• thread #​1: tid = 0xe18ba1, 0x0000000100bd47fc llcllvm::Module::getDwarfVersion(this=0x0000000102c0a960) const + 124 at Module.cpp:463, queue = 'com.apple.main-thread', stop reason = step in frame #​0: 0x0000000100bd47fc llcllvm::Module::getDwarfVersion(this=0x0000000102c0a960) const + 124 at Module.cpp:463
  460 if (!Val)
  461 return dwarf::DWARF_VERSION;
  462 return cast(Val->getValue())->getZExtValue();
  -> 463 }
  464
  465 Comdat *Module::getOrInsertComdat(StringRef Name) {
  466 auto &Entry = *ComdatSymTab.insert(std::make_pair(Name, Comdat())).first;

[llvmbot]

Any idea how to get lldb to display the value of the returned dwarf::DWARF_VERSION in the case with -g?

[DimitryAndric]

mentioned in issue llvm/llvm-bugzilla-archive#23192