[PATCH v3 10/10] scripts/gdb: Decode compressed stack depot frames

[Matt Fleming <matt@readmodwrite.com>]

From: Matt Fleming <mfleming@cloudflare.com>

lx-stack_depot_lookup reads stack_record->entries directly and would
misread compressed frames as full-width addresses. Export
STACK_RECORD_COMPRESSED through constants.py.in and decompress frames
the same way as arch_stack_depot_frame_decompress() on x86-64 and
arm64.

Other architectures never compress frames (the generic hook rejects
compression), but the helper raises an error if it meets compressed
frames there.

Signed-off-by: Matt Fleming <mfleming@cloudflare.com>
---
 scripts/gdb/linux/constants.py.in |  5 +++++
 scripts/gdb/linux/stackdepot.py   | 23 +++++++++++++++++++----
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/scripts/gdb/linux/constants.py.in b/scripts/gdb/linux/constants.py.in
index dab8b80bed69..da6b39c3dc13 100644
--- a/scripts/gdb/linux/constants.py.in
+++ b/scripts/gdb/linux/constants.py.in
@@ -22,6 +22,7 @@
 #include <linux/radix-tree.h>
 #include <linux/maple_tree.h>
 #include <linux/slab.h>
+#include <linux/stackdepot.h>
 #include <linux/threads.h>
 #include <linux/vmalloc.h>
 
@@ -112,6 +113,10 @@ if IS_BUILTIN(CONFIG_PAGE_OWNER):
     LX_GDBPARSED(PAGE_EXT_OWNER)
     LX_GDBPARSED(PAGE_EXT_OWNER_ALLOCATED)
 
+/* linux/stackdepot.h */
+if IS_BUILTIN(CONFIG_STACKDEPOT):
+    LX_GDBPARSED(STACK_RECORD_COMPRESSED)
+
 /* linux/slab.h */
 LX_GDBPARSED(SLAB_RED_ZONE)
 LX_GDBPARSED(SLAB_POISON)
diff --git a/scripts/gdb/linux/stackdepot.py b/scripts/gdb/linux/stackdepot.py
index aaa18af25cd1..f689cacb3cb7 100644
--- a/scripts/gdb/linux/stackdepot.py
+++ b/scripts/gdb/linux/stackdepot.py
@@ -20,6 +20,21 @@ def help():
     gdb.write("Unrecognized command\n")
     raise gdb.GdbError(t)
 
+def stack_record_entry(stack, i):
+    if not int(stack['flags']) & constants.LX_STACK_RECORD_COMPRESSED:
+        return int(stack['entries'][i])
+
+    # Mirror arch_stack_depot_frame_decompress().
+    payload = int(stack['compressed_entries'][i])
+    if utils.is_target_arch("x86-64"):
+        return 0xffffffff00000000 | payload
+    if utils.is_target_arch("aarch64"):
+        text = int(gdb.parse_and_eval("(unsigned long)_text"))
+        if payload & 0x80000000:
+            payload -= 1 << 32
+        return (text + payload) & 0xffffffffffffffff
+    raise gdb.GdbError("compressed stack depot frames are not supported on this architecture\n")
+
 def stack_depot_fetch(handle):
     global DEPOT_STACK_ALIGN
     global stack_record_type
@@ -40,7 +55,7 @@ def stack_depot_fetch(handle):
     pool_index = parts['pool_index_plus_1'] - 1
     if pool_index >= pools_num:
         gdb.write("pool index %d out of bounds (%d) for stack id 0x%08x\n" % (pool_index, pools_num, handle))
-        return gdb.Value(0), 0
+        return [], 0
 
     stack_pools = gdb.parse_and_eval('stack_pools')
 
@@ -48,10 +63,10 @@ def stack_depot_fetch(handle):
         pool = stack_pools[pool_index]
         stack = (pool + gdb.Value(offset).cast(utils.get_size_t_type())).cast(stack_record_type.get_type().pointer())
         size = int(stack['size'].cast(utils.get_ulong_type()))
-        return stack['entries'], size
+        return [stack_record_entry(stack, i) for i in range(size)], size
     except Exception as e:
         gdb.write("%s\n" % e)
-        return gdb.Value(0), 0
+        return [], 0
 
 def stack_depot_print(handle):
     if not constants.LX_CONFIG_STACKDEPOT:
@@ -61,7 +76,7 @@ def stack_depot_print(handle):
     if nr_entries > 0:
         for i in range(0, nr_entries):
             try:
-                gdb.execute("x /i 0x%x" % (int(entries[i])))
+                gdb.execute("x /i 0x%x" % entries[i])
             except Exception as e:
                 gdb.write("%s\n" % e)
 
-- 
2.43.0