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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 a9e186da81
commit 2e30d77a19
8 changed files with 86 additions and 8 deletions
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12
src/backend/tcop/postgres.c
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@ -3415,7 +3415,9 @@ 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)
@ -3425,8 +3427,16 @@ 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