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Suppress warning about stack_base_ptr with late-model GCC.

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GCC 12 complains that set_stack_base is storing the address of
a local variable in a long-lived pointer.  This is an entirely
reasonable warning (indeed, it just helped us find a bug);
but that behavior is intentional here.  We can work around it
by using __builtin_frame_address(0) instead of a specific local
variable; that produces an address a dozen or so bytes different,
in my testing, but we don't care about such a small difference.
Maybe someday a compiler lacking that function will start to issue
a similar warning, but we'll worry about that when it happens.

Patch by me, per a suggestion from Andres Freund.  Back-patch to
v12, which is as far back as the patch will go without some pain.
(Recently-established project policy would permit a back-patch as
far as 9.2, but I'm disinclined to expend the work until GCC 12
is much more widespread.)

Discussion: https://postgr.es/m/3773792.1645141467@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2022-02-17 22:45:34 -05:00
parent f927a6ec3e
commit de447bb8e6
8 changed files with 89 additions and 13 deletions
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20
src/backend/tcop/postgres.c
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@ -129,17 +129,15 @@ static long max_stack_depth_bytes = 100 * 1024L;
/*
* Stack base pointer -- initialized by PostmasterMain and inherited by
* subprocesses. This is not static because old versions of PL/Java modify
* it directly. Newer versions use set_stack_base(), but we want to stay
* binary-compatible for the time being.
* subprocesses (but see also InitPostmasterChild).
*/
char *stack_base_ptr = NULL;
static char *stack_base_ptr = NULL;
/*
* On IA64 we also have to remember the register stack base.
*/
#if defined(__ia64__) || defined(__ia64)
char *register_stack_base_ptr = NULL;
static char *register_stack_base_ptr = NULL;
#endif
/*
@ -3416,7 +3414,9 @@ ia64_get_bsp(void)
pg_stack_base_t
set_stack_base(void)
{
#ifndef HAVE__BUILTIN_FRAME_ADDRESS
char stack_base;
#endif
pg_stack_base_t old;
#if defined(__ia64__) || defined(__ia64)
@ -3426,8 +3426,16 @@ set_stack_base(void)
old = stack_base_ptr;
#endif
/* Set up reference point for stack depth checking */
/*
* Set up reference point for stack depth checking. On recent gcc we use
* __builtin_frame_address() to avoid a warning about storing a local
* variable's address in a long-lived variable.
*/
#ifdef HAVE__BUILTIN_FRAME_ADDRESS
stack_base_ptr = __builtin_frame_address(0);
#else
stack_base_ptr = &stack_base;
#endif
#if defined(__ia64__) || defined(__ia64)
register_stack_base_ptr = ia64_get_bsp();
#endif