Messages in this thread | | | Date | Mon, 16 Nov 2020 16:18:19 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH] samples/ftrace: mark my_tramp[12]? global |
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On Mon, 16 Nov 2020 13:10:57 -0800 Sami Tolvanen <samitolvanen@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?
-- Steve
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