[PATCH 3/3] scripts/qemu-gdb: Support coroutine dumps in coredumps

[Peter Xu]

Dumping coroutines don't yet work with coredumps.  Let's make it work.

We still kept most of the old code because they can be either more
flexible, or prettier.  Only add the fallbacks when they stop working.

Currently the raw unwind is pretty ugly, but it works, like this:

(gdb) qemu bt
Coroutine at 0x7fc474728748:

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 scripts/qemugdb/coroutine.py | 50 +++++++++++++++++++++++++++++++-----
 1 file changed, 43 insertions(+), 7 deletions(-)

diff --git a/scripts/qemugdb/coroutine.py b/scripts/qemugdb/coroutine.py
index 20f76ed37b..b29ee16205 100644
--- a/scripts/qemugdb/coroutine.py
+++ b/scripts/qemugdb/coroutine.py
@@ -46,9 +46,30 @@ def get_jmpbuf_regs(jmpbuf):
         'r15': jmpbuf[JB_R15],
         'rip': glibc_ptr_demangle(jmpbuf[JB_PC], pointer_guard) }
 
-def bt_jmpbuf(jmpbuf):
-    '''Backtrace a jmpbuf'''
-    regs = get_jmpbuf_regs(jmpbuf)
+def symbol_lookup(addr):
+    # Example: "__clone3 + 44 in section .text of /lib64/libc.so.6"
+    result = gdb.execute(f"info symbol {hex(addr)}", to_string=True).strip()
+    return result.split(" in ")[0]
+
+def dump_backtrace(regs):
+    '''
+    Backtrace dump with raw registers, mimic GDB command 'bt'.
+    '''
+    # Here only rbp and rip that matter..
+    rbp = regs['rbp']
+    rip = regs['rip']
+    i = 0
+
+    while rbp:
+        print(f"#{i}\t{symbol_lookup(rip)}")
+        rip = gdb.parse_and_eval(f"*(uint64_t *)(uint64_t)({hex(rbp)} + 8)")
+        rbp = gdb.parse_and_eval(f"*(uint64_t *)(uint64_t)({hex(rbp)})")
+        i += 1
+
+def dump_backtrace_live(regs):
+    '''
+    Backtrace dump with gdb's 'bt' command, only usable in a live session.
+    '''
     old = dict()
 
     # remember current stack frame and select the topmost
@@ -69,6 +90,17 @@ def bt_jmpbuf(jmpbuf):
 
     selected_frame.select()
 
+def bt_jmpbuf(jmpbuf):
+    '''Backtrace a jmpbuf'''
+    regs = get_jmpbuf_regs(jmpbuf)
+    try:
+        # This reuses gdb's "bt" command, which can be slightly prettier
+        # but only works with live sessions.
+        dump_backtrace_live(regs)
+    except:
+        # If above doesn't work, fallback to poor man's unwind
+        dump_backtrace(regs)
+
 def co_cast(co):
     return co.cast(gdb.lookup_type('CoroutineUContext').pointer())
 
@@ -101,10 +133,14 @@ def invoke(self, arg, from_tty):
 
         gdb.execute("bt")
 
-        if gdb.parse_and_eval("qemu_in_coroutine()") == False:
-            return
-
-        co_ptr = gdb.parse_and_eval("qemu_coroutine_self()")
+        try:
+            # This only works with a live session
+            co_ptr = gdb.parse_and_eval("qemu_coroutine_self()")
+            if co_ptr == False:
+                return
+        except:
+            # Fallback to use hard-coded ucontext vars if it's coredump
+            co_ptr = gdb.parse_and_eval("co_tls_current")
 
         while True:
             co = co_cast(co_ptr)
-- 
2.47.0