[Lldb-commits] [PATCH] D122411: [lldb][AArch64] Fix corefile memory reads when there are non-address bits

[David Spickett via Phabricator via lldb-commits]

DavidSpickett updated this revision to Diff 418246.
DavidSpickett added a comment.

- Corefile down to 24k with some tweaking of coredump_filter
- Add some prints so when you generate the corefile you know what addresses to test

I also found another bug testing this where memory read works but printing
doesnt, like:

  (lldb) p (char*)0x0000ffff90027000
  (char *) $1 = 0x0000ffff90027000 "LLDB"
  (lldb) p (char*)0xff0afffff7ff9000
  (char *) $2 = 0xff0afffff7ff9000 ""

I think this may use the number of addressable bits setting, that could be missing
in a corefile. Planning changes to work on that and add tests for it.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D122411/new/

https://reviews.llvm.org/D122411

Files:
  lldb/source/Plugins/ABI/AArch64/ABISysV_arm64.cpp
  lldb/test/API/linux/aarch64/non_address_bit_memory_access/TestAArch64LinuxNonAddressBitMemoryAccess.py
  lldb/test/API/linux/aarch64/non_address_bit_memory_access/corefile
  lldb/test/API/linux/aarch64/non_address_bit_memory_access/main.c


Index: lldb/test/API/linux/aarch64/non_address_bit_memory_access/main.c
===================================================================
--- lldb/test/API/linux/aarch64/non_address_bit_memory_access/main.c
+++ lldb/test/API/linux/aarch64/non_address_bit_memory_access/main.c
@@ -13,6 +13,13 @@
   if (buf == MAP_FAILED)
     return 1;
 
+  // Some known values to go in the corefile, since we cannot
+  // write to corefile memory.
+  buf[0] = 'L';
+  buf[1] = 'L';
+  buf[2] = 'D';
+  buf[3] = 'B';
+
 #define sign_ptr(ptr) __asm__ __volatile__("pacdza %0" : "=r"(ptr) : "r"(ptr))
 
   // Set top byte to something.
@@ -21,5 +28,11 @@
   // Address is now:
   // <8 bit top byte tag><pointer signature><virtual address>
 
+  // Uncomment this line to crash and generate a corefile.
+  // Prints so we know what fixed address to look for in testing.
+  // printf("buf: %p\n", buf);
+  // printf("buf_with_non_address: %p\n", buf_with_non_address);
+  // *(char*)0 = 0;
+
   return 0; // Set break point at this line.
 }
Index: lldb/test/API/linux/aarch64/non_address_bit_memory_access/TestAArch64LinuxNonAddressBitMemoryAccess.py
===================================================================
--- lldb/test/API/linux/aarch64/non_address_bit_memory_access/TestAArch64LinuxNonAddressBitMemoryAccess.py
+++ lldb/test/API/linux/aarch64/non_address_bit_memory_access/TestAArch64LinuxNonAddressBitMemoryAccess.py
@@ -175,3 +175,19 @@
 
             if not found_read_buf:
                 self.fail("Did not find any reads of buf.")
+
+    @skipIfLLVMTargetMissing("AArch64")
+    def test_non_address_bit_memory_corefile(self):
+        self.runCmd("target create --core corefile")
+
+        self.expect("thread list", substrs=['stopped',
+                                            'stop reason = signal SIGSEGV'])
+
+        # No caching (the program/corefile are the cache) and no writing
+        # to memory. So just check that tagged/untagged addresses read
+        # the same location.
+
+        expected = ["4c 4c 44 42", "LLDB"]
+        # These are known addresses in the corefile.
+        self.expect("memory read 0x0000ffffa75a5000", substrs=expected)
+        self.expect("memory read 0xff0bffffa75a5000", substrs=expected)
Index: lldb/source/Plugins/ABI/AArch64/ABISysV_arm64.cpp
===================================================================
--- lldb/source/Plugins/ABI/AArch64/ABISysV_arm64.cpp
+++ lldb/source/Plugins/ABI/AArch64/ABISysV_arm64.cpp
@@ -794,14 +794,20 @@
 // Reads code or data address mask for the current Linux process.
 static lldb::addr_t ReadLinuxProcessAddressMask(lldb::ProcessSP process_sp,
                                                 llvm::StringRef reg_name) {
-  // Linux configures user-space virtual addresses with top byte ignored.
-  // We set default value of mask such that top byte is masked out.
-  uint64_t address_mask = ~((1ULL << 56) - 1);
-  // If Pointer Authentication feature is enabled then Linux exposes
-  // PAC data and code mask register. Try reading relevant register
-  // below and merge it with default address mask calculated above.
+  // 0 means there isn't a mask or it has not been read yet.
+  // We do not return the top byte mask unless thread_sp is valid.
+  // This prevents calls to this function before the thread is setup locking
+  // in the value to just the top byte mask, in cases where pointer authentication
+  // might also be active.
+  uint64_t address_mask = 0;
   lldb::ThreadSP thread_sp = process_sp->GetThreadList().GetSelectedThread();
   if (thread_sp) {
+    // Linux configures user-space virtual addresses with top byte ignored.
+    // We set default value of mask such that top byte is masked out.
+    address_mask = ~((1ULL << 56) - 1);
+    // If Pointer Authentication feature is enabled then Linux exposes
+    // PAC data and code mask register. Try reading relevant register
+    // below and merge it with default address mask calculated above.
     lldb::RegisterContextSP reg_ctx_sp = thread_sp->GetRegisterContext();
     if (reg_ctx_sp) {
       const RegisterInfo *reg_info =


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