https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77837
Bug ID: 77837
Summary: missing -Wformat-length warning for %p with null
argument on powerpc64
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
When configured for most *-linux targets with Glibc, including s390x, sparc,
and x86_64, GCC prints the warnings below for the following program as expected
because Glibc %p formats null arguments as "(nil)":
$ cat t.c && /build/sysroot/sparc-unknown-linux/bin/sparc-unknown-linux-gcc -S
-Wall t.c
char d[5];
void f (void)
{
__builtin_sprintf (d + 0, "%p", (void*)0);
__builtin_sprintf (d + 4, "%p", (void*)0);
}
t.c: In function 'f':
t.c:5:32: warning: writing a terminating nul past the end of the destination
[-Wformat-length=]
__builtin_sprintf (d + 0, "%p", (void*)0);
~~^
t.c:5:3: note: format output 6 bytes into a destination of size 5
__builtin_sprintf (d + 0, "%p", (void*)0);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
t.c:6:30: warning: '%p' directive writing 5 bytes into a region of size 1
[-Wformat-length=]
__builtin_sprintf (d + 4, "%p", (void*)0);
^~
t.c:6:3: note: format output 6 bytes into a destination of size 1
__builtin_sprintf (d + 4, "%p", (void*)0);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
However, when configured for powerpc64* (either as a native compiler or a
cross-compiler), it prints just the following, indicating that it thinks that
%p with a null argument produces a single digit, which is contrary to the Glibc
implementation:
t.c:6:32: warning: writing a terminating nul past the end of the destination
[-Wformat-length=]
__builtin_sprintf (d + 4, "%p", (void*)0);
~~^
t.c:6:3: note: format output 2 bytes into a destination of size 1
__builtin_sprintf (d + 4, "%p", (void*)0);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This appears to be because the %p format expected by GCC is determined by a
printf_pointer_format target hook which is initialized to the
gnu_libc_printf_pointer_format function in most back ends for Linux except in
rs6000.o. There it's initialized to the default_printf_pointer_format
function. The target hook initialization is the result of expanding the
TARGET_PRINTF_POINTER_FORMAT macro, which is defined to
gnu_libc_printf_pointer_format in the config/linux.h header. This header is,
in turn, included by most back ends for Linux but not by rs6000.c
