* Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx> wrote: > > One more fundamental question: why do we have the __do_sys_waitid() and > > __inline_sys_waitid() distinction - aren't the function call signatures the same > > with no conversion done? > > > > I.e. couldn't we just do a single, static __do_sys_waitid(), where the compiler > > would decide to what extent inlining is justified? This would allow the compiler > > to inline all the intermediate code into the stubs themselves. > > > > Or is this a side effect of the error injection feature, which needs to add extra > > logic at this intermediate level? That too should be able to use the > > __do_sys_waitid() variant though. > > Error injection is unrelated. It seems to be for three reasons, if I read > the code (include/linux/syscalls.h) correctly: > > asmlinkage long __do_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) > > 1) This takes arguments of type long (to protect against CVE-2009-0029); > see https://lwn.net/Articles/604287/ : "Digging into the history of > this, it turns out that the long version ensures that 32-bit values > are correctly sign-extended for some 64-bit kernel platforms, > preventing a historical vulnerability." > > { > long ret = __in_sys##name(__MAP(x,__SC_CAST,__VA_ARGS__)); > __MAP(x,__SC_TEST,__VA_ARGS__); I see - so it's _not_ the same function call signature, but a wrapper with a sign-extended version, which is fair and useful. So on architectures where this matters there's type conversion and active code generated. Thanks, Ingo
