On 26 March 2015 at 23:15, Andrew Morton <a...@linux-foundation.org> wrote: > On Thu, 26 Mar 2015 14:58:40 -0700 Joe Perches <j...@perches.com> wrote: > >> > I'd have thought that a function-wide >> > __attribute__((__string_section__(foo)) >> > wouldn't be a ton of work to implement. >> >> Maybe not. >> >> Could some future version of gcc move string constants >> in a function to a specific section marked in a manner >> similar to what Andrew described above? > > One thing which might complexicate this is > > void foo() > { > p("bar"); > } > > void __attribute__((__string_section__(.init.rodata)) zot() > { > p("bar"); > } > > It would be silly to create two instances of "bar".
No it wouldn't, because the "bar" in foo() has a different life time than the "bar" in zot(). The compiler simply cannot know what the life time of a section will be, so can only merge string within the same section. Beside that, your example is wrong and would generate a section mismatch because zot() is not marked with __init so it's a function that can be called after init. If one does, however, that p() will get passed a dangling pointer. That's what modpost will complain about. > > Change it thusly: > > > #define __mark_str(str) \ > ({ static const char var[] > __attribute__((__section__(".init.string"))) = str; var; }) > > void foo() > { > p("bar"); > } > > void zot() > { > p(__mark_str("bar")); > } > > > and we indeed get two copies of "bar". > > It would be nice not to do that, but I guess that losing this > optimization is a reasonable compromise. As I said, it's legit to get two copies here, as the compiler simply cannot deduce any semantics from the section name. However, this is a synthetic example as in real life use-cases you'll only seldom have the same format string be used twice. So this is, at best, a minor issue. Thanks, Mathias