On 9/23/20 9:44 AM, Szabolcs Nagy wrote:
The 09/23/2020 09:22, Szabolcs Nagy wrote:
The 09/21/2020 12:45, Martin Sebor via Gcc-patches wrote:
On 9/21/20 12:20 PM, Vaseeharan Vinayagamoorthy wrote:
After this patch, I am seeing this -Warray-parameter error:
In file included from ../include/pthread.h:1,
from ../sysdeps/nptl/thread_db.h:25,
from ../nptl/descr.h:32,
from ../sysdeps/aarch64/nptl/tls.h:44,
from ../include/errno.h:25,
from ../sysdeps/unix/sysv/linux/sysdep.h:23,
from ../sysdeps/unix/sysv/linux/generic/sysdep.h:22,
from ../sysdeps/unix/sysv/linux/aarch64/sysdep.h:24,
from <stdin>:1:
../sysdeps/nptl/pthread.h:734:47: error: argument 1 of type ‘struct
__jmp_buf_tag *’ declared as a pointer [-Werror=array-parameter=]
734 | extern int __sigsetjmp (struct __jmp_buf_tag *__env, int __savemask)
__THROWNL;
| ~~~~~~~~~~~~~~~~~~~~~~^~~~~
In file included from ../include/setjmp.h:2,
from ../nptl/descr.h:24,
from ../sysdeps/aarch64/nptl/tls.h:44,
from ../include/errno.h:25,
from ../sysdeps/unix/sysv/linux/sysdep.h:23,
from ../sysdeps/unix/sysv/linux/generic/sysdep.h:22,
from ../sysdeps/unix/sysv/linux/aarch64/sysdep.h:24,
from <stdin>:1:
../setjmp/setjmp.h:54:46: note: previously declared as an array ‘struct
__jmp_buf_tag[1]’
54 | extern int __sigsetjmp (struct __jmp_buf_tag __env[1], int
__savemask) __THROWNL;
| ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
cc1: all warnings being treated as errors
The warning flags differences between the forms of array parameters
in redeclarations of the same function, including pointers vs arrays
as in this instance. It needs to be suppressed in glibc, either by
making the function declarations consistent, or by #pragma diagnostic.
(IIRC, the pointer declaration comes before struct __jmp_buf_tag has
been defined so simply using the array form there doesn't work without
defining the type first.)
I would expect the warning to be suppressed when using the installed
library thanks to -Wno-system-headers.
why is this a warning? i'm not convinced it
should be in -Wall.
The main motivation for the warning is to detect unintentional
inconsistencies between function redeclarations that make deriving
true true intent difficult or impossible (e.g, T[3] vs T[1], or
T[] vs T[1], or equivalently T* vs T[1]).
One goal is to support the convention where a constant array bound
in a function array parameter is used in lieu of the [static N]
notation (i.e., the minimum number of elements the caller is
expected to make available). The [static N] notation is little
known, used only exceedingly rarely, and isn't available in C++.
The array notation is used more often, although by no means common.
The ultimate goal is to motivate users to take advantage of GCC's
ability to check ordinary functions for out-of-bounds accesses to
array arguments. The checking is only feasible if all declarations
of the same function, including its definition, use a consistent
notation to specify the same bound. Including the strict
-Warray-parameter=2 setting in -Wall helps support this goal
(-Warray-parameter=1 doesn't warn for mismatches in the forms
of ordinary array bounds without [static].)
I mentioned the results of testing the patch with a number of
packages, including Glibc, Binutils/GDB, Glibc, and the kernel,
in the overview of the patch series:
https://gcc.gnu.org/pipermail/gcc-patches/2020-July/550920.html
It explains why I chose not to relax the warning to accommodate
the Glibc use case.
Based on my admittedly limited testing I'm not concerned about
the warning having adverse effects. But if broader excposure
shows that it is prone to some it can certainly be adjusted.
Jeff does periodic mass rebuilds of all of Fedora with the top
of GCC trunk so we should know soon.
Martin
this is a warning with false positives that
have no portable workaround and does not
really help catching bugs (at least i doubt
inconsistent array vs pointer declaration
is causing common problems).
what gcc should warn about is if there is an
array style argument declaration and a caller
passes an array that's provably shorter than
that.
i take this back: such warning only makes
sense when the static keyword is used in
the array declarator.
i really think this issue should be fixed
in gcc and not in glibc: it's not true that
the argument has array type, the standard
requires the parameter type to be adjusted:
A declaration of a parameter as "array of type"
shall be adjusted to "qualified pointer to type"
this warning will just confuse users and
make them believe that the two declaration
styles for pointer arguments are somehow
different.
