On Mon, Oct 02, 2017 at 12:29:45PM -0700, Kees Cook wrote: > On Mon, Sep 25, 2017 at 12:41 PM, Segher Boessenkool > <segher@xxxxxxxxxxxxxxxxxxx> wrote: > > On Mon, Sep 25, 2017 at 04:01:55PM +0000, David Laight wrote: > >> From: Segher Boessenkool > >> > The compiler puts this item in .sdata, for 32-bit. There is no .srodata, > >> > so if it wants to use a small data section, it must use .sdata . > >> > > >> > Non-external, non-referenced symbols are not put in .sdata, that is the > >> > difference you see with the "static". > >> > > >> > I don't think there is a bug here. If you think there is, please open > >> > a GCC bug. > >> > >> The .sxxx sections are for 'small' data that can be accessed (typically) > >> using small offsets from a global register. > >> This means that all sections must be adjacent in the image. > >> So you can't really have readonly small data. > >> > >> My guess is that the linker script is putting .srodata in with .sdata. > > > > .srodata does not *exist* (in the ABI). > > So, I still think this is a bug. The variable is marked const: this is > not a _suggestion_. :) If the compiler produces output where the > variable is writable, that's a bug. C11 6.7.3/6: "If an attempt is made to modify an object defined with a const-qualified type through use of an lvalue with non-const-qualified type, the behavior is undefined." And that is all that "const" means. The compiler is free to put this var in *no* data section, or to copy it to the stack before using it, or anything else it thinks is a good idea. If you think it would be a good idea for the compiler to change its behaviour here, please file a PR (or send a patch). Please bring arguments why we would want to change this. > I can't tell if this bug is related: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=9571 I don't think so: the only remaining bug there is that a copy of the constant is put in .rodata.cst8 (although there is a copy in .sdata2 already). Thanks, Segher -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
