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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 0dc0284ade
commit 46b738ffc2
8 changed files with 86 additions and 8 deletions
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2
src/backend/postmaster/postmaster.c
View File

@@ -1028,7 +1028,7 @@ PostmasterMain(int argc, char *argv[])
/*
* Set reference point for stack-depth checking.
*/
set_stack_base();
(void) set_stack_base();
/*
* Initialize pipe (or process handle on Windows) that allows children to

12
src/backend/tcop/postgres.c
View File

@@ -3280,7 +3280,9 @@ 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)
@@ -3290,8 +3292,16 @@ 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

11
src/backend/utils/init/miscinit.c
View File

@@ -93,13 +93,12 @@ InitPostmasterChild(void)
IsUnderPostmaster = true; /* we are a postmaster subprocess now */
/*
* Set reference point for stack-depth checking. We re-do that even in the
* !EXEC_BACKEND case, because there are some edge cases where processes
* are started with an alternative stack (e.g. starting bgworkers when
* running postgres using the rr debugger, as bgworkers are launched from
* signal handlers).
* Set reference point for stack-depth checking. This might seem
* redundant in !EXEC_BACKEND builds; but it's not because the postmaster
* launches its children from signal handlers, so we might be running on
* an alternative stack.
*/
set_stack_base();
(void) set_stack_base();
InitProcessGlobals();