[Lldb-commits] [PATCH] D68533: Explicitly set entry point arch when it's thumb [Second Try]

[António Afonso via Phabricator via lldb-commits]

aadsm created this revision.
aadsm added reviewers: clayborg, labath, wallace, espindola.
aadsm added a project: LLDB.

This is a redo of D68069 <https://reviews.llvm.org/D68069> because I reverted it due to some concerns that were now addressed along with the new comments that @labath added.

I found a case where the main android binary (app_process32) had thumb code at its entry point but no entry in the symbol table indicating this. This made lldb set a 4 byte breakpoint at that address (we default to arm code) instead of a 2 byte one (like we should for thumb).
The big deal with this is that the expression evaluator uses the entry point as a way to know when a JITed expression has finished executing by putting a breakpoint there. Because of this, evaluating expressions on certain android devices (Google Pixel something) made the process crash.
This was fixed by checking this specific situation when we parse the symbol table and add an artificial symbol for this 2 byte range and indicating that it's arm thumb.

I created 2 unit tests for this, one to check that now we know that the entry point is arm thumb, and the other to make sure we didn't change the behaviour for arm code.

I also run the following on the command line with the `app_process32` where I found the issue:
**Before:**

  (lldb) dis -s 0x1640 -e 0x1644
  app_process32[0x1640]: .long  0xf0004668                ; unknown opcode

**After:**

  (lldb) dis -s 0x1640 -e 0x1644
  app_process32`:
  app_process32[0x1640] <+0>: mov    r0, sp
  app_process32[0x1642]:      andeq  r0, r0, r0


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D68533

Files:
  lldb/lit/SymbolFile/Breakpad/symtab.test
  lldb/lit/SymbolFile/dissassemble-entry-point.s
  lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
  lldb/unittests/ObjectFile/ELF/TestObjectFileELF.cpp

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