From cd55085b07e03aba28cc5a5358852efb1beb1a15 Mon Sep 17 00:00:00 2001
From: Luis Machado <luis.machado@linaro.org>
Date: Mon, 15 Jun 2020 15:44:20 -0300
Subject: AArch64: Report tag violation error information

Whenever a memory tag violation occurs, we get a SIGSEGV. Additional
information can be obtained through the siginfo data structure.

For AArch64 the Linux kernel may expose the fault address and tag
information, if we have a synchronous event. Otherwise there is
not fault address available.

gdb/ChangeLog:

YYYY-MM-DD  Luis Machado  <luis.machado@linaro.org>

	* aarch64-linux-tdep.c
	(aarch64_linux_handle_segmentation_fault): New function.
	(aarch64_linux_init_abi): Register
	aarch64_linux_handle_segmentation_fault as segmentation fault hook.
	* arch/aarch64-linux.h (SEGV_MTEAERR): Define.
	(SEGV_MTESERR): Define.
---
 gdb/aarch64-linux-tdep.c     | 54 ++++++++++++++++++++++++++++++++++++++++++++
 gdb/arch/aarch64-mte-linux.h |  6 +++++
 2 files changed, 60 insertions(+)

diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
index 892977d..c8fccdd 100644
--- a/gdb/aarch64-linux-tdep.c
+++ b/gdb/aarch64-linux-tdep.c
@@ -1644,6 +1644,57 @@ aarch64_linux_memtag_to_string (struct gdbarch *gdbarch,
   return string_printf ("0x%s", phex_nz (tag, sizeof (tag)));
 }
 
+/* AArch64 Linux implementation of the handle_segmentation_fault gdbarch
+   hook.  Displays information about possible memory tag violations.  */
+
+static void
+aarch64_linux_handle_segmentation_fault (struct gdbarch *gdbarch,
+					 struct ui_out *uiout)
+{
+  CORE_ADDR fault_addr = 0;
+  long si_code = 0;
+  CORE_ADDR ltag;
+  CORE_ADDR atag;
+
+  try
+    {
+      /* Sigcode tells us if the segfault is actually a memory tag
+	 violation.  */
+      si_code = parse_and_eval_long ("$_siginfo.si_code\n");
+
+      fault_addr
+	= parse_and_eval_long ("$_siginfo._sifields._sigfault.si_addr");
+    }
+  catch (const gdb_exception &exception)
+    {
+      return;
+    }
+
+  /* If this is not a memory tag violation, just return.  */
+  if (si_code != SEGV_MTEAERR && si_code != SEGV_MTESERR)
+    return;
+
+  uiout->text ("\n");
+
+  uiout->field_string ("sigcode-meaning", _("Memory tag violation"));
+  uiout->text (_(" while accessing address "));
+  uiout->field_core_addr ("fault-addr", gdbarch, fault_addr);
+  uiout->text ("\n");
+
+  uiout->text (_("Logical tag "));
+  ltag = aarch64_linux_get_ltag (fault_addr);
+  uiout->field_core_addr ("logical-tag", gdbarch, ltag);
+  uiout->text ("\n");
+
+  if (aarch64_linux_get_atag (fault_addr, &atag) != 0)
+    uiout->text (_("Allocation tag unavailable"));
+  else
+    {
+      uiout->text (_("Allocation tag "));
+      uiout->field_core_addr ("allocation-tag", gdbarch, atag);
+    }
+}
+
 static void
 aarch64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 {
@@ -1724,6 +1775,9 @@ aarch64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 
       /* Register a hook for converting a memory tag to a string.  */
       set_gdbarch_memtag_to_string (gdbarch, aarch64_linux_memtag_to_string);
+
+      set_gdbarch_handle_segmentation_fault (gdbarch,
+				      aarch64_linux_handle_segmentation_fault);
     }
 
   /* Initialize the aarch64_linux_record_tdep.  */
diff --git a/gdb/arch/aarch64-mte-linux.h b/gdb/arch/aarch64-mte-linux.h
index 4ee6de3..79c662c 100644
--- a/gdb/arch/aarch64-mte-linux.h
+++ b/gdb/arch/aarch64-mte-linux.h
@@ -35,6 +35,12 @@
 #define MTE_LOGICAL_TAG_START_BIT   56
 #define MTE_LOGICAL_MAX_VALUE	    0xf
 
+/* Memory tagging definitions.  */
+#ifndef SEGV_MTEAERR
+# define SEGV_MTEAERR 8
+# define SEGV_MTESERR 9
+#endif
+
 /* Return the number of tag granules in the memory range
    [ADDR, ADDR + LEN) given GRANULE_SIZE.  */
 extern int get_tag_granules (CORE_ADDR addr, size_t len,
-- 
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