From: Greg KH gregkh@linuxfoundation.org Date: Thu, 18 Aug 2022 14:26:14 +0200
On Thu, Aug 18, 2022 at 01:53:04PM +0200, Alexander Lobakin wrote:
Macro TO_NATIVE() directly takes a reference to its argument @x without making an intermediate variable. This makes compilers emit build warnings and errors if @x is an expression or a deref of a const pointer (when target Endianness != host Endianness):
scripts/mod/modpost.h:87:18: error: lvalue required as unary '&' operand
87 | __endian(&(x), &(__x), sizeof(__x)); \ | ^scripts/mod/sympath.c:19:25: note: in expansion of macro 'TO_NATIVE' 19 | #define t(x) TO_NATIVE(x) | ^~~~~~~~~ scripts/mod/sympath.c:100:31: note: in expansion of macro 't' 100 | eh->e_shoff = t(h(eh->e_shoff) + off);
scripts/mod/modpost.h:87:24: warning: passing argument 2 of '__endian'
discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers] 87 | __endian(&(x), &(__x), sizeof(__x)); \ | ^~~~~~ scripts/mod/sympath.c:18:25: note: in expansion of macro 'TO_NATIVE' 18 | #define h(x) TO_NATIVE(x) | ^~~~~~~~~ scripts/mod/sympath.c:178:48: note: in expansion of macro 'h' 178 | iter < end; iter = (void *)iter + h(eh->e_shentsize)) {
How come this hasn't shown up in cross-builds today?
It doesn't happen with the current code.
Create a temporary variable, assign @x to it and don't use @x after that. This makes it possible to pass expressions as an argument. Also, do a cast-away for the second argument when calling __endian() to avoid 'discarded qualifiers' warning, as typeof() preserves qualifiers and makes compilers think that we're passing pointer to a const.
Reported-by: kernel test robot lkp@intel.com Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org # 4.9+
Where are these build warnings showing up at that we don't see them today, yet this is needed to go back to all stable trees?
I thought all fixes should go to the applicable stable trees, am I wrong? If so, I'll drop the tag in the next spin.
I remember we had such discussion already regarding fixing stuff in modpost, which can happen only with never mainlained GCC LTO or with the in-dev code. At the end that fix made it into the stables IIRC.
still confused,
greg k-h
Thanks, Olek