Re: [PATCH v2 2/5] avoid -Wuse-after-free [BZ #26779]

[Martin Sebor <msebor@gmail.com>]

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On 1/24/22 17:52, Martin Sebor wrote:
> This is a repost of the original patch but broken down by source
> file and with some suppression done by #pragma GCC diagnostic
> instead of conversion to intptr_t.  It also adds fixes for
> the same problem in the test suite that I overlooked before.

The attached patch suppresses the -Wuse-after-free instance in
intl/localealias.c.

> 
> On 1/15/22 17:21, Martin Sebor wrote:
>> GCC 12 features a couple of new warnings designed to detect uses
>> of pointers made invalid by the pointees lifetimes having ended.
>> Building Glibc with the enhanced GCC exposes a few such uses,
>> mostly after successful calls to realloc.  The attached patch
>> avoids the new warnings by converting the pointers to uintptr_t
>> first and using the converted integers instead.
>>
>> The patch suppresses all instances of the warning at the strictest
>> setting (-Wuse-after-free=3), which includes even uses in equality
>> expressions.  The default setting approved for GCC 12 is
>> -Wuse-after-free=2, which doesn't warn on such uses to accommodate
>> the pointer-adjustment-after-realloc idiom.  At the default setting,
>> the changes to ldconfig.c and setenv are not necessary.
>>
>> Martin
> 

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diff --git a/intl/localealias.c b/intl/localealias.c
index 3ae360f40d..b36092363a 100644
--- a/intl/localealias.c
+++ b/intl/localealias.c
@@ -318,7 +318,15 @@ read_alias_file (const char *fname, int fname_len)
 
 		  if (string_space_act + alias_len + value_len > string_space_max)
 		    {
-		      /* Increase size of memory pool.  */
+#pragma GCC diagnostic push
+
+#if defined __GNUC__ && __GNUC__ >= 12
+  /* Suppress the valid GCC 12 warning until the code below is changed
+     to avoid using pointers to the reallocated block.  */
+#  pragma GCC diagnostic ignored "-Wuse-after-free"
+#endif
+
+		    /* Increase size of memory pool.  */
 		      size_t new_size = (string_space_max
 					 + (alias_len + value_len > 1024
 					    ? alias_len + value_len : 1024));
@@ -351,6 +359,8 @@ read_alias_file (const char *fname, int fname_len)
 					   value, value_len);
 		  string_space_act += value_len;
 
+#pragma GCC diagnostic pop
+
 		  ++nmap;
 		  ++added;
 		}