https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97100
Bug ID: 97100
Summary: -Wformat checks all arms of _Generic leading to
irrelevant type expectation warnings
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: sherzberg+gcc at freeshell dot org
Target Milestone: ---
Created attachment 49238
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49238&action=edit
preprocessed output
The Wformat printf/scanf checker will produce warnings for all arms of a
generic expression, even those which will not be included in the program. This
can produce a fairly large number of warnings, since the macro below will
produce a warning for many of its arms for each use of the macro.
This is sort of code used in _Generic tutorials, and mostly nowhere else, that
can produce a large number of irrelevant warnings:
#define DISPLAY(x) \
_Generic(x, int: printf("%d\r\n", x), \
char: printf("%c\r\n", x), \
float: printf("%.3f\r\n", x))
$ gcc-10 -v -save-temps -Wall generic_test.c
Using built-in specs.
COLLECT_GCC=gcc-10
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/10/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
10-20200411-0ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-10/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-10
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-gnu-unique-object --disable-vtable-verify --enable-plugin
--enable-default-pie --with-system-zlib --enable-libphobos-checking=release
--with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch
--disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none,amdgcn-amdhsa,hsa --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.0.1 20200411 (experimental) [master revision
bb87d5cc77d:75961caccb7:f883c46b4877f637e0fa5025b4d6b5c9040ec566] (Ubuntu
10-20200411-0ubuntu1)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/10/cc1 -E -quiet -v -imultiarch x86_64-linux-gnu
generic_test.c -mtune=generic -march=x86-64 -Wall -fpch-preprocess
-fasynchronous-unwind-tables -fstack-protector-strong -Wformat-security
-fstack-clash-protection -fcf-protection -o generic_test.i
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/10/include-fixed"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-linux-gnu/10/include
/usr/local/include
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/10/cc1 -fpreprocessed generic_test.i -quiet
-dumpbase generic_test.c -mtune=generic -march=x86-64 -auxbase generic_test
-Wall -version -fasynchronous-unwind-tables -fstack-protector-strong
-Wformat-security -fstack-clash-protection -fcf-protection -o generic_test.s
GNU C17 (Ubuntu 10-20200411-0ubuntu1) version 10.0.1 20200411 (experimental)
[master revision
bb87d5cc77d:75961caccb7:f883c46b4877f637e0fa5025b4d6b5c9040ec566]
(x86_64-linux-gnu)
compiled by GNU C version 10.0.1 20200411 (experimental) [master
revision bb87d5cc77d:75961caccb7:f883c46b4877f637e0fa5025b4d6b5c9040ec566], GMP
version 6.2.0, MPFR version 4.0.2, MPC version 1.1.0, isl version
isl-0.22.1-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C17 (Ubuntu 10-20200411-0ubuntu1) version 10.0.1 20200411 (experimental)
[master revision
bb87d5cc77d:75961caccb7:f883c46b4877f637e0fa5025b4d6b5c9040ec566]
(x86_64-linux-gnu)
compiled by GNU C version 10.0.1 20200411 (experimental) [master
revision bb87d5cc77d:75961caccb7:f883c46b4877f637e0fa5025b4d6b5c9040ec566], GMP
version 6.2.0, MPFR version 4.0.2, MPC version 1.1.0, isl version
isl-0.22.1-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: d7d6d629e7a95e97eb10596483b5a39e
generic_test.c: In function ‘main’:
generic_test.c:10:32: warning: format ‘%d’ expects argument of type ‘int’, but
argument 2 has type ‘double’ [-Wformat=]
10 | DISPLAY(1.0f);
| ^
| |
| double
generic_test.c:10:62: warning: format ‘%c’ expects argument of type ‘int’, but
argument 2 has type ‘double’ [-Wformat=]
10 | DISPLAY(1.0f);
| ^
|
|
|
double
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-mtune=generic' '-march=x86-64'
as -v --64 -o generic_test.o generic_test.s
GNU assembler version 2.34 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Ubuntu) 2.34
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/10/collect2 -plugin
/usr/lib/gcc/x86_64-linux-gnu/10/liblto_plugin.so
-plugin-opt=/usr/lib/gcc/x86_64-linux-gnu/10/lto-wrapper
-plugin-opt=-fresolution=generic_test.res -plugin-opt=-pass-through=-lgcc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s --build-id
--eh-frame-hdr -m elf_x86_64 --hash-style=gnu --as-needed -dynamic-linker
/lib64/ld-linux-x86-64.so.2 -pie -z now -z relro
/usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/Scrt1.o
/usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/crti.o
/usr/lib/gcc/x86_64-linux-gnu/10/crtbeginS.o -L/usr/lib/gcc/x86_64-linux-gnu/10
-L/usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu
-L/usr/lib/gcc/x86_64-linux-gnu/10/../../../../lib -L/lib/x86_64-linux-gnu
-L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib
-L/usr/lib/gcc/x86_64-linux-gnu/10/../../.. generic_test.o -lgcc --push-state
--as-needed -lgcc_s --pop-state -lc -lgcc --push-state --as-needed -lgcc_s
--pop-state /usr/lib/gcc/x86_64-linux-gnu/10/crtendS.o
/usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/crtn.o
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-mtune=generic' '-march=x86-64'
