Created attachment 1859018 [details]
preprocessed source

Description of problem:
On ppc64le:

=======================================================================
[mockbuild@3a00fe7f7f694de19171916d75a4f441 h5dump]$ cat test.c
#include <stdio.h>
#include <stdarg.h>

static char buf[4096];
static char gfmt[] = "%Lg";

static int __attribute__ ((noinline)) 
foo(char *str, const char *fmt, ...) {
	int ret;
	va_list ap;
	va_start(ap, fmt);
	ret = vsnprintf(str, 4096, fmt, ap);
	va_end(ap);
	return ret;
}

int main(void) {
	long double dval = 128;
	int ret = foo(buf, gfmt, dval);

	fprintf(stdout, "ret[%d]\n", ret);
	fprintf(stdout, "buf[%s]\n", buf);

	return 0;
}
[mockbuild@3a00fe7f7f694de19171916d75a4f441 h5dump]$ gcc -D_GNU_SOURCE -D_POSIX_C_SOURCE=200809L   -DNDEBUG -UH5_DEBUG_API -I../../../src  -std=c99  -Wall -Wcast-qual -Wconversion -Wextra -Wfloat-equal -Wformat=2 -Winit-self -Winvalid-pch -Wmissing-include-dirs -Wno-c++-compat -Wno-format-nonliteral -Wshadow -Wundef -Wwrite-strings -pedantic -Wlarger-than=2560 -Wlogical-op -Wframe-larger-than=16384 -Wpacked-bitfield-compat -Wsync-nand -Wstrict-overflow=5 -Wno-unsuffixed-float-constants -Wdouble-promotion -Wtrampolines -Wstack-usage=8192 -Wmaybe-uninitialized -Wdate-time -Warray-bounds=2 -Wc99-c11-compat -Wduplicated-cond -Whsa -Wnormalized -Wnull-dereference -Wunused-const-variable -Walloca -Walloc-zero -Wduplicated-branches -Wformat-overflow=2 -Wformat-truncation=1 -Wrestrict -Wattribute-alias -Wcast-align=strict -Wshift-overflow=2 -Wattribute-alias=2 -Wmissing-profile -Wc11-c2x-compat -fstdarg-opt -fdiagnostics-urls=never -fno-diagnostics-color -s -Wno-aggregate-return -Wno-inline -Wno-missing-format-attribute -Wno-missing-noreturn -Wno-overlength-strings -Wno-jump-misses-init -Wno-suggest-attribute=const -Wno-suggest-attribute=noreturn -Wno-suggest-attribute=pure -Wno-suggest-attribute=format -Wno-suggest-attribute=cold -Wno-suggest-attribute=malloc  -Wbad-function-cast -Wimplicit-function-declaration -Wmissing-declarations -Wmissing-prototypes -Wnested-externs -Wold-style-definition -Wpacked -Wpointer-sign -Wpointer-to-int-cast -Wredundant-decls -Wstrict-prototypes -Wswitch -Wunused-function -Wunused-variable -Wunused-parameter -Wcast-align -Wunused-but-set-variable -Wformat -Wincompatible-pointer-types -Wshadow -Wcast-function-type -Wmaybe-uninitialized -O3 -O2 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1  -m64 -mcpu=power8 -mtune=power8 -fasynchronous-unwind-tables -fstack-clash-protection -o testfoo test.c && ./testfoo
test.c:4:13: warning: size of 'buf' 4096 bytes exceeds maximum object size 2560 [-Wlarger-than=]
    4 | static char buf[4096];
      |             ^~~
ret[1]
buf[0]
=======================================================================


Apparently the result is not okay, with -O0:
ret[3]
buf[128]


Version-Release number of selected component (if applicable):
gcc-12.0.1-0.4.fc36.ppc64le

How reproducible:
100%