On Fri, 9 Nov 2018 14:34:59 -0600 Josh Poimboeuf <[email protected]> wrote:
I'm slowly massaging this to work with tracepoints. But I hit a snag on this patch. > On Fri, Nov 09, 2018 at 02:57:46PM -0500, Steven Rostedt wrote: > > On Fri, 9 Nov 2018 13:35:05 -0600 > > Josh Poimboeuf <[email protected]> wrote: > > > > > > > > > +#define DECLARE_STATIC_CALL(key, func) > > > > > \ > > > > > + extern struct static_call_key key; > > > > > \ > > > > > + extern typeof(func) STATIC_CALL_TRAMP(key); > > > > > \ > > > > > + /* Preserve the ELF symbol so objtool can access it: */ > > > > > \ > > > > > + __ADDRESSABLE(key) > > > > > > > > Does the __ADDRESSABLE(key) need to be in the DECLARE part? > > > > If so, there needs to be more explanation than just the comment above > > > > it. > > > > > > For each call site, objtool creates a struct in .static_call_sites: > > > > > > struct static_call_site { > > > s32 addr; > > > s32 key; > > > }; > > > > > > In order to do that, it needs to create a relocation which references > > > the key symbol. If the key is defined in another .o file, then the > > > current .o will not have an ELF symbol associated with the key. The > > > __ADDRESSABLE(key) thing tells GCC to leave the key symbol in the .o > > > file, even though it's not referenced anywhere. That makes objtool's > > > job easier, so it doesn't have to edit the symbol table. > > > > > > I could add a comment saying as much, though it's hard to explain it in > > > fewer words than I just did :-) > > > > Does this have to do with adding the references by relative address? > > > > In record_mcount, I just picked an existing symbol and referenced that.. > > But perhaps this is a cleaner way. > > I think recordmcount is different. It creates references (in > __mcount_loc) to functions which are already in the object file, so they > already have symbols associated with them. > > But in this case, when objtool is creating references, the symbol it > needs to reference is outside the .o file, so there's no symbol to > associate it with. > The __ADDRESSABLE() appears to fail if you have a header with a DECLARE_STATIC_CALL() that is included where the DEFINE_STATIC_CALL() is, because I'm getting this: In file included from <command-line>: /work/git/linux-trace.git/include/linux/compiler.h:285:11: error: redefinition of ‘__addressable___tp_func_sys_enter40’ __PASTE(__addressable_##sym, __LINE__) = (void *)&sym; ^~~~~~~~~~~~~~ /work/git/linux-trace.git/include/linux/compiler_types.h:53:23: note: in definition of macro ‘___PASTE’ #define ___PASTE(a,b) a##b ^ /work/git/linux-trace.git/include/linux/compiler.h:285:3: note: in expansion of macro ‘__PASTE’ __PASTE(__addressable_##sym, __LINE__) = (void *)&sym; ^~~~~~~ /work/git/linux-trace.git/include/linux/static_call.h:112:2: note: in expansion of macro ‘__ADDRESSABLE’ __ADDRESSABLE(key) ^~~~~~~~~~~~~ /work/git/linux-trace.git/include/linux/static_call.h:115:2: note: in expansion of macro ‘DECLARE_STATIC_CALL’ DECLARE_STATIC_CALL(key, _func); \ ^~~~~~~~~~~~~~~~~~~ /work/git/linux-trace.git/include/linux/tracepoint.h:310:2: note: in expansion of macro ‘DEFINE_STATIC_CALL’ DEFINE_STATIC_CALL(__tp_func_##name, __tracepoint_iter_##name); ^~~~~~~~~~~~~~~~~~ /work/git/linux-trace.git/include/trace/define_trace.h:42:2: note: in expansion of macro ‘DEFINE_TRACE_FN’ DEFINE_TRACE_FN(name, reg, unreg, PARAMS(proto), PARAMS(args)) ^~~~~~~~~~~~~~~ /work/git/linux-trace.git/include/trace/events/syscalls.h:18:1: note: in expansion of macro ‘TRACE_EVENT_FN’ TRACE_EVENT_FN(sys_enter, ^~~~~~~~~~~~~~ /work/git/linux-trace.git/include/linux/compiler.h:285:11: note: previous definition of ‘__addressable___tp_func_sys_enter40’ was here __PASTE(__addressable_##sym, __LINE__) = (void *)&sym; ^~~~~~~~~~~~~~ /work/git/linux-trace.git/include/linux/compiler_types.h:53:23: note: in definition of macro ‘___PASTE’ #define ___PASTE(a,b) a##b ^ /work/git/linux-trace.git/include/linux/compiler.h:285:3: note: in expansion of macro ‘__PASTE’ __PASTE(__addressable_##sym, __LINE__) = (void *)&sym; ^~~~~~~ /work/git/linux-trace.git/include/linux/static_call.h:112:2: note: in expansion of macro ‘__ADDRESSABLE’ __ADDRESSABLE(key) ^~~~~~~~~~~~~ /work/git/linux-trace.git/include/linux/tracepoint.h:234:2: note: in expansion of macro ‘DECLARE_STATIC_CALL’ DECLARE_STATIC_CALL(__tp_func_##name, __tracepoint_iter_##name); \ ^~~~~~~~~~~~~~~~~~~ /work/git/linux-trace.git/include/linux/tracepoint.h:421:2: note: in expansion of macro ‘__DECLARE_TRACE’ __DECLARE_TRACE(name, PARAMS(proto), PARAMS(args), \ ^~~~~~~~~~~~~~~ /work/git/linux-trace.git/include/linux/tracepoint.h:560:2: note: in expansion of macro ‘DECLARE_TRACE’ DECLARE_TRACE(name, PARAMS(proto), PARAMS(args)) ^~~~~~~~~~~~~ /work/git/linux-trace.git/include/trace/events/syscalls.h:18:1: note: in expansion of macro ‘TRACE_EVENT_FN’ TRACE_EVENT_FN(sys_enter, The complaint is on: DEFINE_STATIC_CALL(__tp_func_##name, __tracepoint_iter_##name); And the previous definition is on: DECLARE_STATIC_CALL(__tp_func_##name, __tracepoint_iter_##name); \ -- Steve
