On Mon, Nov 16, 2020 at 1:18 PM Steven Rostedt <rost...@goodmis.org> wrote: > > On Mon, 16 Nov 2020 13:10:57 -0800 > Sami Tolvanen <samitolva...@google.com> wrote: > > > Clang doesn't warn about this as we're building a module, it just > > generates a reference to a non-existing global "my_tramp" symbol, > > because the one defined in inline assembly has a local binding: > > > > $ readelf --symbols --wide ftrace-direct.lto.o | grep my_tramp > > 16: 0000000000000000 13 FUNC LOCAL DEFAULT 1 my_tramp > > 33: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND my_tramp > > 42: 0000000000000000 8 FUNC GLOBAL HIDDEN 8 my_tramp.cfi_jt > > > > This would prevent the module from loading, which modpost catches: > > > > ERROR: modpost: "my_tramp" [samples/ftrace/ftrace-direct.ko] undefined! > > > > > From user space, I'm just using the following file: > > > > As this error happens only with Control-Flow Integrity, we need to > > take the address of the "test" function to force the compiler to > > generate a jump table entry for it. Here's a slightly tweaked > > stand-alone reproducer: > > > > https://godbolt.org/z/GnzjE4 > > Thanks, we don't need to look more into this. It was mostly my curiosity to > find a way to have the compiler know about a function declared statically > in inline assembly. Maybe I'm asking for too much ;-) > > I'll take your original patch. Does it need to go to stable, or is this not > that big of an issue to allow it to be added in the next merge window?
Thanks! This is definitely not a big issue, it just fixes the allyesconfig build with CFI, and it's not needed in -stable. Sami
