[Lldb-commits] [lldb] [lldb] Infer GPR base size from registers when target arch is unset (PR #203498)

[Charles Zablit via lldb-commits]

https://github.com/charles-zablit created https://github.com/llvm/llvm-project/pull/203498

`ABIX86::AugmentRegisterInfo()` picks between the i386 and amd64 register maps using `process->GetTarget().GetArchitecture().GetAddressByteSize()`. However, on Windows, `process attach -p` reaches this code with an empty Target ArchSpec. `GetAddressByteSize()` returns 0 and lldb falls through to the i386 map.

This patch falls back to scanning the register list itself:
- `rax/rsp/rip`: amd64
- `eax/esp/eip`: i386.

This patch fixes `TestRegisters::test_convenience_registers_with_process_attach` and `TestRegisters::test_convenience_registers_16bit_with_process_attach` on Windows using `LLDB_USE_LLDB_SERVER=1`.

>From a3c29c43098bcd8ff36938d837a7bc977b3ad835 Mon Sep 17 00:00:00 2001
From: Charles Zablit <c_zablit at apple.com>
Date: Fri, 12 Jun 2026 11:28:22 +0100
Subject: [PATCH] [lldb] Infer GPR base size from registers when target arch is
 unset

---
 lldb/source/Plugins/ABI/X86/ABIX86.cpp | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/lldb/source/Plugins/ABI/X86/ABIX86.cpp b/lldb/source/Plugins/ABI/X86/ABIX86.cpp
index db170700d3f65..e905aed21d1af 100644
--- a/lldb/source/Plugins/ABI/X86/ABIX86.cpp
+++ b/lldb/source/Plugins/ABI/X86/ABIX86.cpp
@@ -207,6 +207,20 @@ void ABIX86::AugmentRegisterInfo(
 
   uint32_t gpr_base_size =
       process_sp->GetTarget().GetArchitecture().GetAddressByteSize();
+  // Determine the GPR base size. Prefer the target architecture, but fall
+  // back to the register list itself when the target arch isn't set yet
+  if (gpr_base_size == 0) {
+    for (const auto &reg : regs) {
+      if (reg.name == "rax" || reg.name == "rsp" || reg.name == "rip") {
+        gpr_base_size = 8;
+        break;
+      }
+      if (reg.name == "eax" || reg.name == "esp" || reg.name == "eip") {
+        gpr_base_size = 4;
+        break;
+      }
+    }
+  }
 
   // primary map from a base register to its subregisters
   BaseRegToRegsMap base_reg_map = makeBaseRegMap(gpr_base_size == 8);