sgraenitz created this revision.
sgraenitz added reviewers: labath, JDevlieghere, bkoropoff, clayborg.
Herald added subscribers: MaskRay, arichardson, aprantl, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLDB.
First part of a fix for JITed code debugging. This has been a regression from
5.0 to 6.0 and it's is still reproducible on current master:
https://bugs.llvm.org/show_bug.cgi?id=36209
The address of the breakpoint site is corrupt: the 0x4 value we end up with,
looks like an offset on a zero base address. When we parse the ELF section
headers from the JIT descriptor, the load address for the text section we find
in `header.sh_addr` is correct.
The bug manifests in `VMAddressProvider::GetVMRange(const ELFSectionHeader &)`
(follow it from `ObjectFileELF::CreateSections()`). Here we think the object
type was `eTypeObjectFile` and unleash some extra logic [1] which essentially
overwrites the address with a zero value.
The object type is deduced from the ELF header's `e_type` in
`ObjectFileELF::CalculateType()`. It never returns `eTypeJIT`, because the ELF
header has no representation for it [2]. Instead the in-memory ELF object
states `ET_REL`, which leads to `eTypeObjectFile`. This is what we get from
`lli` at least since 3.x. (Might it be better to write `ET_EXEC` on the JIT
side instead? In fact, relocations were already applied at this point, so
"Relocatable" is not quite exact.)
So, this patch proposes to set `eTypeJIT` explicitly whenever we read from a
JIT descriptor. In `ObjectFileELF::CreateSections()` we can then call
`GetType()`, which returns the explicit value or otherwise falls back to
`CalculateType()`.
LLDB then sets the breakpoint successfully. Next step: debug info.
Process 1056 stopped
* thread #1, name = 'lli', stop reason = breakpoint 1.2
frame #0: 0x00007ffff7ff7000 JIT(0x3ba2030)`jitbp()
JIT(0x3ba2030)`jitbp:
-> 0x7ffff7ff7000 <+0>: pushq %rbp
0x7ffff7ff7001 <+1>: movq %rsp, %rbp
0x7ffff7ff7004 <+4>: movabsq $0x7ffff7ff6000, %rdi ; imm =
0x7FFFF7FF6000
0x7ffff7ff700e <+14>: movabsq $0x7ffff6697e80, %rcx ; imm =
0x7FFFF6697E80
[1] It was first introduced with
https://reviews.llvm.org/D38142#change-lF6csxV8HdlL, which has also been the
original breaking change. The code has changed a lot since then.
[2] ELF object types:
https://github.com/llvm/llvm-project/blob/2d2277f5/llvm/include/llvm/BinaryFormat/ELF.h#L110
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D61611
Files:
lldb/source/Plugins/JITLoader/GDB/JITLoaderGDB.cpp
lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
Index: lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
===================================================================
--- lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
+++ lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
@@ -1865,7 +1865,7 @@
return;
m_sections_up = llvm::make_unique<SectionList>();
- VMAddressProvider address_provider(CalculateType());
+ VMAddressProvider address_provider(GetType());
size_t LoadID = 0;
for (const auto &EnumPHdr : llvm::enumerate(ProgramHeaders())) {
Index: lldb/source/Plugins/JITLoader/GDB/JITLoaderGDB.cpp
===================================================================
--- lldb/source/Plugins/JITLoader/GDB/JITLoaderGDB.cpp
+++ lldb/source/Plugins/JITLoader/GDB/JITLoaderGDB.cpp
@@ -327,6 +327,10 @@
FileSpec(jit_name), symbolfile_addr, symbolfile_size);
if (module_sp && module_sp->GetObjectFile()) {
+ // Object formats (like ELF) have no representation for a JIT type.
+ // We will get it wrong, if we deduce it from the header.
+ module_sp->GetObjectFile()->SetType(ObjectFile::eTypeJIT);
+
// load the symbol table right away
module_sp->GetObjectFile()->GetSymtab();
Index: lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
===================================================================
--- lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
+++ lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
@@ -1865,7 +1865,7 @@
return;
m_sections_up = llvm::make_unique<SectionList>();
- VMAddressProvider address_provider(CalculateType());
+ VMAddressProvider address_provider(GetType());
size_t LoadID = 0;
for (const auto &EnumPHdr : llvm::enumerate(ProgramHeaders())) {
Index: lldb/source/Plugins/JITLoader/GDB/JITLoaderGDB.cpp
===================================================================
--- lldb/source/Plugins/JITLoader/GDB/JITLoaderGDB.cpp
+++ lldb/source/Plugins/JITLoader/GDB/JITLoaderGDB.cpp
@@ -327,6 +327,10 @@
FileSpec(jit_name), symbolfile_addr, symbolfile_size);
if (module_sp && module_sp->GetObjectFile()) {
+ // Object formats (like ELF) have no representation for a JIT type.
+ // We will get it wrong, if we deduce it from the header.
+ module_sp->GetObjectFile()->SetType(ObjectFile::eTypeJIT);
+
// load the symbol table right away
module_sp->GetObjectFile()->GetSymtab();
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