Re: [PATCH 05/08] PR jit/63854: Fix double-initialization within tree-pretty-print.c

[Jeff Law <law@redhat.com>]

On 11/25/14 18:39, David Malcolm wrote:
> Running various JIT testcases under valgrid showed this one-time leak:
>
> 8,464 (336 direct, 8,128 indirect) bytes in 1 blocks are definitely lost in loss record 144 of 147
>     at 0x4A081D4: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
>     by 0x5DF4EA0: xcalloc (xmalloc.c:162)
>     by 0x5DB0D9C: pretty_printer::pretty_printer(char const*, int) (pretty-print.c:777)
>     by 0x54DA67D: __static_initialization_and_destruction_0(int, int) (tree-pretty-print.c:66)
>     by 0x54DA6AF: _GLOBAL__sub_I_tree_pretty_print.c (tree-pretty-print.c:3542)
>     by 0x309540F2D9: call_init.part.0 (dl-init.c:82)
>     by 0x309540F3C2: _dl_init (dl-init.c:34)
>     by 0x3095401229: ??? (in /usr/lib64/ld-2.18.so)
>     by 0x1: ???
>     by 0xFFEFFFFBE: ???
>     by 0xFFEFFFFDA: ???
>
> tree-pretty-print.c:66 is:
>    static pretty_printer buffer;
>
> pretty-print.c:777 is:
> pretty_printer::pretty_printer (const char *p, int l)
>    : buffer (new (XCNEW (output_buffer)) output_buffer ()),
>
> This is the ctor of "buffer" (the pretty_printer) running at startup
> by the dynamic linker, allocating its "buffer" output_buffer field
> and the pair of obstacks it contains.
>
> [Arguably "buffer" is a poor name for a pretty_printer, and these
> should be named "pp" or somesuch, though that seems like it should
> be a separate patch, which I'll do as a followup].
>
> However, this ctor gets rerun the first time that
> maybe_init_pretty_print is called, reallocating the output_buffer and
> its obstacks, leaking the old ones:
>
>   static void
>   maybe_init_pretty_print (FILE *file)
>   {
>     if (!initialized)
>       {
>         new (&buffer) pretty_printer ();
>         /* etc */
>       }
>     /* etc */
>   }
>
> This is a one-time leak, so it's worth fixing mostly for the sake of
> keeping the valgrind output clean.
>
> Having objects with non-empty ctors/dtors in a statically-allocated
> section feels like too much C++ to me: we can't rely on the order in
> which they run, and in the past I've been bitten by runtimes that
> didn't support them fully (where the compiler worked, but the
> linker/startup code didn't).
>
> Hence this patch fixes the leak by rewriting the global "buffer" to
> be a pointer, allocating the pp on the heap, eliminating the
> before-main static ctor/dtor pair.
>
> gcc/ChangeLog:
> 	PR jit/63854
> 	* tree-pretty-print.c: Eliminate include of <new>.
> 	(buffer): Convert this variable from a pretty_printer to a
> 	pretty_printer *.
> 	(initialized): Eliminate this variable in favor of the NULL-ness
> 	of "buffer".
> 	(print_generic_decl): Update for "buffer" becoming a pointer.
> 	(print_generic_stmt): Likewise.
> 	(print_generic_stmt_indented): Likewise.
> 	(print_generic_expr): Likewise.
> 	(maybe_init_pretty_print): Likewise, allocating "buffer" on the
> 	heap and using its non-NULL-ness to ensure idempotency.
OK.

Jeff