Re: [PATCH] gdb: add HtabPrinter to gdb-gdb.py.in

[Simon Marchi <simark@simark.ca>]

On 2/27/23 13:10, Tom Tromey wrote:
>>>>>> "Simon" == Simon Marchi via Gdb-patches <gdb-patches@sourceware.org> writes:
> 
> Simon> When debugging GDB, I find it a bit tedious to inspect htab_t objects.
> Simon> It is possible to find the entries by poking at the fields, but it's
> Simon> annoying to do each time.  I think a pretty printer would help.  Add a
> Simon> basic one to gdb-gdb.py.
> 
> I could have used this today :-}
> 
> Simon> +    def _children_generator(self):
> Simon> +        size = int(self._val["size"])
> Simon> +        entries = self._val["entries"]
> Simon> +
> Simon> +        child_i = 0
> Simon> +        for entries_i in range(size):
> Simon> +            entry = entries[entries_i]
> Simon> +            # 0 (NULL pointer) means there's nothing, 1 (HTAB_DELETED_ENTRY)
> Simon> +            # means there was something, but is now deleted.
> Simon> +            if int(entry) in (0, 1):
> Simon> +                continue
> Simon> +
> Simon> +            yield (str(child_i), entry)
> Simon> +            child_i += 1
> Simon> +
> Simon> +    def children(self):
> Simon> +        return self._children_generator()
> 
> I don't think the indirection here is needed, you can just have children
> yield.  But, either way seems fine to me.
> 
> Reviewed-By: Tom Tromey <tom@tromey.com>

Ah, you're right.  Well, here's an updated version that also adds a test
in gdb.gdb/python-helper.exp.


From 69259c470aaad72b28b4d34a5f1d0a999f660582 Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@efficios.com>
Date: Thu, 9 Feb 2023 14:50:56 -0500
Subject: [PATCH] gdb: add HtabPrinter to gdb-gdb.py.in

When debugging GDB, I find it a bit tedious to inspect htab_t objects.
It is possible to find the entries by poking at the fields, but it's
annoying to do each time.  I think a pretty printer would help.  Add a
basic one to gdb-gdb.py.

The pretty printer advertises itself as "array-like", and the result
looks like:

    (top-gdb) p bfcache
    $3 = htab_t with 3 elements = {0x6210003252a0, 0x62100032caa0, 0x62100033baa0}

The htab_t itself doesn't know about the type of pointed objects.  But
it's easy enough to cast the addresses to the right type to use them:

    (top-gdb) print *((btrace_frame_cache *) 0x6210003252a0)
    $6 = {tp = 0x61700002ed80, frame = 0x6210003251e0, bfun = 0x62000000b390}

Change-Id: Ia692e3555fe7a117b7ec087840246b1260a704c6
Reviewed-By: Tom Tromey <tom@tromey.com>
---
 gdb/gdb-gdb.py.in                       | 31 +++++++++++++++++++++++++
 gdb/testsuite/gdb.gdb/python-helper.exp |  3 +++
 2 files changed, 34 insertions(+)

diff --git a/gdb/gdb-gdb.py.in b/gdb/gdb-gdb.py.in
index 95b7d84966f0..56d063cd506b 100644
--- a/gdb/gdb-gdb.py.in
+++ b/gdb/gdb-gdb.py.in
@@ -369,6 +369,35 @@ class IntrusiveListPrinter:
         return self._children_generator()
 
 
+class HtabPrinter:
+    """Pretty-printer for htab_t hash tables."""
+
+    def __init__(self, val):
+        self._val = val
+
+    def display_hint(self):
+        return "array"
+
+    def to_string(self):
+        n = int(self._val["n_elements"]) - int(self._val["n_deleted"])
+        return "htab_t with {} elements".format(n)
+
+    def children(self):
+        size = int(self._val["size"])
+        entries = self._val["entries"]
+
+        child_i = 0
+        for entries_i in range(size):
+            entry = entries[entries_i]
+            # 0 (NULL pointer) means there's nothing, 1 (HTAB_DELETED_ENTRY)
+            # means there was something, but is now deleted.
+            if int(entry) in (0, 1):
+                continue
+
+            yield (str(child_i), entry)
+            child_i += 1
+
+
 def type_lookup_function(val):
     """A routine that returns the correct pretty printer for VAL
     if appropriate.  Returns None otherwise.
@@ -383,6 +412,8 @@ def type_lookup_function(val):
         return CoreAddrPrettyPrinter(val)
     elif tag is not None and tag.startswith("intrusive_list<"):
         return IntrusiveListPrinter(val)
+    elif name == "htab_t":
+        return HtabPrinter(val)
     return None
 
 
diff --git a/gdb/testsuite/gdb.gdb/python-helper.exp b/gdb/testsuite/gdb.gdb/python-helper.exp
index f1e95fbe5ee7..16b419984cf3 100644
--- a/gdb/testsuite/gdb.gdb/python-helper.exp
+++ b/gdb/testsuite/gdb.gdb/python-helper.exp
@@ -208,6 +208,9 @@ proc test_python_helper {} {
 		    " cplus_stuff = $hex}"]
     gdb_test -prompt $outer_prompt_re "print *type->main_type" $answer
 
+    # Test the htab_t pretty-printer.
+    gdb_test -prompt $outer_prompt_re "print all_bfds" "htab_t with ${::decimal} elements = \\{${::hex}.*\\}"
+
     return 0
 }
 

base-commit: 26c294bd1b8d95b421487294863eb1560b65580d
-- 
2.39.2