Summary:
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
Reviewers: labath, JDevlieghere, bkoropoff, clayborg, espindola, alexshap, stella.stamenova
Reviewed By: labath, clayborg
Subscribers: probinson, emaste, aprantl, arichardson, MaskRay, AlexDenisov, yurydelendik, lldb-commits
Tags: #lldb
Differential Revision: https://reviews.llvm.org/D61611
llvm-svn: 360354