From: Ian Jackson <ian.jackson@eu.citrix.com>
Date: Tue, 24 Oct 2017 16:00:44 +0000 (+0100)
Subject: fishdescriptor: try parse_eval_via_print
X-Git-Tag: archive/debian/6.0.0~1^2~14
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=chiark-utils.git;a=commitdiff_plain;h=33545a21597767a50443a717b015fc9e3c8dd553;ds=sidebyside

fishdescriptor: try parse_eval_via_print

Actually this works for reading errno but not for setting it.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
---

diff --git a/fishdescriptor/py/fishdescriptor/indonor.py b/fishdescriptor/py/fishdescriptor/indonor.py
index f01f9eb..f701434 100644
--- a/fishdescriptor/py/fishdescriptor/indonor.py
+++ b/fishdescriptor/py/fishdescriptor/indonor.py
@@ -6,6 +6,7 @@ import copy
 import os
 import sys
 import socket
+import re
 
 def _string_bytearray(s):
     # gets us bytes in py2 and py3
@@ -56,6 +57,15 @@ def parse_eval(expr):
     sys.stderr.flush()
     return x
 
+def parse_eval_via_print(expr):
+    # works only with things whose value is an int and where expr is simple
+    sys.stderr.write("##  EVAL-VIA-PRINT %s\n" % repr(expr))
+    x = gdb.execute('print %s' % expr, to_string=True)
+    m = re.match('\$\d+ = (\d+)\n$', x) # seriously !
+    r = int(m.group(1))
+    sys.stderr.write('##  => %s\n' % r)
+    return 4
+
 class DonorStructLayout():
     def __init__(l, typename):
         x = gdb.lookup_type(typename)
@@ -172,13 +182,22 @@ class DonorImplementation():
         return 1
 
     def _errno_save(di):
-        di._saved_errno = parse_eval('errno')
+        # incomprehensibly, gdb.parse_and_eval('errno') can sometimes
+        # fail with
+        #   gdb.error: Cannot find thread-local variables on this target
+        # even though plain gdb `print errno' works.
+        # OMG.  This may be related to:
+        #  https://github.com/cloudburst/libheap/issues/24
+        # although I can't find it in the gdb bug db (which is half-broken
+        # in my browser)
+        # Anyway:
+        di._saved_errno = parse_eval_via_print('errno')
 
     def _errno_restore(di):
         to_restore = di._saved_errno
         di._saved_errno = None
         if to_restore is not None:
-            parse_eval('errno = %d' % to_restore)
+            parse_eval_via_print('errno = %d' % to_restore)
 
     def _result(di, output):
         sys.stderr.write("#> %s" % output)