Suppress warning about stack_base_ptr with late-model GCC.

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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@ -381,6 +381,28 @@ fi])# PGAC_CHECK_BUILTIN_FUNC
# PGAC_CHECK_BUILTIN_FUNC_PTR
# -----------------------
# Like PGAC_CHECK_BUILTIN_FUNC, except that the function is assumed to
# return a pointer type, and the argument(s) should be given literally.
# This handles some cases that PGAC_CHECK_BUILTIN_FUNC doesn't.
AC_DEFUN([PGAC_CHECK_BUILTIN_FUNC_PTR],
[AC_CACHE_CHECK(for $1, pgac_cv$1,
[AC_LINK_IFELSE([AC_LANG_PROGRAM([
void *
call$1(void)
{
return $1($2);
}], [])],
[pgac_cv$1=yes],
[pgac_cv$1=no])])
if test x"${pgac_cv$1}" = xyes ; then
AC_DEFINE_UNQUOTED(AS_TR_CPP([HAVE$1]), 1,
[Define to 1 if your compiler understands $1.])
fi])# PGAC_CHECK_BUILTIN_FUNC_PTR
# PGAC_PROG_VARCC_VARFLAGS_OPT
# ----------------------------
# Given a compiler, variable name and a string, check if the compiler

40
configure vendored
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@ -15944,6 +15944,46 @@ cat >>confdefs.h <<_ACEOF
#define HAVE__BUILTIN_POPCOUNT 1
_ACEOF
fi
# __builtin_frame_address may draw a diagnostic for non-constant argument,
# so it needs a different test function.
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_frame_address" >&5
$as_echo_n "checking for __builtin_frame_address... " >&6; }
if ${pgac_cv__builtin_frame_address+:} false; then :
$as_echo_n "(cached) " >&6
else
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */
void *
call__builtin_frame_address(void)
{
return __builtin_frame_address(0);
}
int
main ()
{
;
return 0;
}
_ACEOF
if ac_fn_c_try_link "$LINENO"; then :
pgac_cv__builtin_frame_address=yes
else
pgac_cv__builtin_frame_address=no
fi
rm -f core conftest.err conftest.$ac_objext \
conftest$ac_exeext conftest.$ac_ext
fi
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv__builtin_frame_address" >&5
$as_echo "$pgac_cv__builtin_frame_address" >&6; }
if test x"${pgac_cv__builtin_frame_address}" = xyes ; then
cat >>confdefs.h <<_ACEOF
#define HAVE__BUILTIN_FRAME_ADDRESS 1
_ACEOF
fi
# We require 64-bit fseeko() to be available, but run this check anyway

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@ -1769,6 +1769,9 @@ PGAC_CHECK_BUILTIN_FUNC([__builtin_bswap64], [long int x])
PGAC_CHECK_BUILTIN_FUNC([__builtin_clz], [unsigned int x])
PGAC_CHECK_BUILTIN_FUNC([__builtin_ctz], [unsigned int x])
PGAC_CHECK_BUILTIN_FUNC([__builtin_popcount], [unsigned int x])
# __builtin_frame_address may draw a diagnostic for non-constant argument,
# so it needs a different test function.
PGAC_CHECK_BUILTIN_FUNC_PTR([__builtin_frame_address], [0])
# We require 64-bit fseeko() to be available, but run this check anyway
# in case it finds that _LARGEFILE_SOURCE has to be #define'd for that.

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@ -1033,7 +1033,7 @@ 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

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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

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@ -95,13 +95,12 @@ 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();

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@ -745,6 +745,9 @@
/* Define to 1 if your compiler understands __builtin_ctz. */
#undef HAVE__BUILTIN_CTZ
/* Define to 1 if your compiler understands __builtin_frame_address. */
#undef HAVE__BUILTIN_FRAME_ADDRESS
/* Define to 1 if your compiler understands __builtin_$op_overflow. */
#undef HAVE__BUILTIN_OP_OVERFLOW

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@ -441,6 +441,7 @@ sub GenerateFiles
HAVE__BUILTIN_CLZ => undef,
HAVE__BUILTIN_CONSTANT_P => undef,
HAVE__BUILTIN_CTZ => undef,
HAVE__BUILTIN_FRAME_ADDRESS => undef,
HAVE__BUILTIN_OP_OVERFLOW => undef,
HAVE__BUILTIN_POPCOUNT => undef,
HAVE__BUILTIN_TYPES_COMPATIBLE_P => undef,