Le 12/12/2019 à 13:51, Christoph Hellwig a écrit :
Why can't current_stack_pointer be turned into an inline function using inline assembly? That would reduce the overhead for all callers.
In the old days, it was a macro, and it was changed into an assembly function by commit https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=bfe9a2cfe91a
It was later renamed from __get_SP() to current_stack_pointer() by commit https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=acf620ecf56cfc4edaffaf158250e128539cdd26
But in fact this function is badly named as it doesn't provide the current stack pointer but a pointer to the parent's stack frame.
Having it as an extern function forces GCC to set a stack frame in the calling function. If inline assembly is used instead, there's a risk of not getting a stack frame in the calling function, in which case the current_stack_pointer() will return the grandparent's stackframe pointer instead of the parent's one.
Christophe
