2018-08-28 19:55 GMT+09:00 Arnd Bergmann <arnd@xxxxxxxx>: > On Mon, Aug 27, 2018 at 10:44 PM Daniel Santos <daniel.santos@xxxxxxxxx> wrote: >> >> On 08/27/2018 03:09 PM, Nick Desaulniers wrote: >> >> Now we're back to the question of "what do you mean by 'constant'"? If >> >> you mean a C constant expression (as defined in the C standard) than >> >> almost none of this code fits that criteria. For these compile-time >> >> assertions to work, we are concerned with the data flow analysis and >> >> constant propagation performed by the compiler during optimization. You >> >> will notice in include/linux/compiler.h that __compiletime_assert is a >> >> no-op when __OPTIMIZE__ is not defined. >> > Depending on optimizations for static assertions sounds problematic. >> >> (with my best Palpatine voice) It is unavoidable. >> >> Actually it's theoretically possible, but the compiler would have to do >> something akin to copying it's control flow graph et. al, run -O2-ish >> optimizations, perform the static assertions and then throw away the >> optimized control flow graph and emit code based upon the original. > > In the context of the kernel, compiling with anything less than -O2 or > -Os is not an issue, we don't do it anyway. -O0 never worked, and > AFAICT we only build one file with -O1, but that is something we can do > away with as well: > > from fs/reiserfs/Makefile: > # gcc -O2 (the kernel default) is overaggressive on ppc32 when many inline > # functions are used. This causes the compiler to advance the stack > # pointer out of the available stack space, corrupting kernel space, > # and causing a panic. Since this behavior only affects ppc32, this ifeq > # will work around it. If any other architecture displays this behavior, > # add it here. > ccflags-$(CONFIG_PPC32) := $(call cc-ifversion, -lt, 0400, -O1) > > Arnd Recently, I sent out patches to remove redundant GCC version checks, including this one. https://lore.kernel.org/patchwork/patch/977808/ I do not know who is maintaining reiserfs, though. -- Best Regards Masahiro Yamada
