Strange compiler message related to legacystorage.c

[vdr-projects]

Strange compiler message related to legacystorage.c

[madmartin]

Hi, can you please add the compiler name and version and the full commandline where this messages occur?

[pbiering]

command line in front of the error:

g++  -O3 -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  -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -fPIC -Werror=overloaded-virtual -Wno-parentheses -std=gnu++14 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -Wl,-z,relro -Wl,--as-needed  -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld  -shared osdteletext.o menu.o txtfont.o txtrecv.o txtrender.o displaybase.o display.o storage.o legacystorage.o packedstorage.o rootdir.o setup.o -o libvdr-osdteletext.so
In member function 'write',
    inlined from 'save' at txtrecv.c:194:21:
legacystorage.c:131:25: warning: 'write' reading 3612 bytes from a region of size 12 [-Wstringop-overread]
  131 |    if (!(written=::write((int)stream, ptr, size)) ) {
      |                         ^
legacystorage.c: In member function 'save':
storage.h:34:18: note: source object 'pageheader' of size 12
   34 |    unsigned char pageheader[12];     // 12 chars (extracted from 8 chars of line X/0)
      |                  ^
/usr/include/unistd.h:367:16: note: in a call to function 'write' declared with attribute 'access (read_only, 2, 3)'
  367 | extern ssize_t write (int __fd, const void *__buf, size_t __n) __wur
      |                ^
In member function 'write',
    inlined from 'write' at legacystorage.c:129:9,
    inlined from 'save' at txtrecv.c:194:21:
legacystorage.c:135:24: warning: 'write' reading 3612 bytes from a region of size 12 [-Wstringop-overread]
  135 |          return ::write((int)stream, ptr, size);
      |                        ^
legacystorage.c: In member function 'save':
storage.h:34:18: note: source object 'pageheader' of size 12
   34 |    unsigned char pageheader[12];     // 12 chars (extracted from 8 chars of line X/0)
      |                  ^
/usr/include/unistd.h:367:16: note: in a call to function 'write' declared with attribute 'access (read_only, 2, 3)'
  367 | extern ssize_t write (int __fd, const void *__buf, size_t __n) __wur
      |                ^

Compiler

g++ -v
Using built-in specs.
COLLECT_GCC=/usr/bin/g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/11/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,objc,obj-c++,ada,go,d,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl=/builddir/build/BUILD/gcc-11.2.1-20210728/obj-x86_64-redhat-linux/isl-install --enable-offload-targets=nvptx-none --without-cuda-driver --enable-gnu-indirect-function --enable-cet --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.1 20210728 (Red Hat 11.2.1-1) (GCC) 

Potentially the issue can get circumvented in case of a "union" will be defined mapping the structure into a simple byte-array and use the byte-array pointer to store the content.