On Thu, May 09, 2019 at 03:49:02PM -0400, Steven Rostedt wrote: > > From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx> > > There's two methods of enabling function tracing in Linux on x86. One is > with just "gcc -pg" and the other is "gcc -pg -mfentry". The former will use > calls to a special function "mcount" after the frame is set up in all C > functions. The latter will add calls to a special function called "fentry" > as the very first instruction of all C functions. > > At compile time, there is a check to see if gcc supports, -mfentry, and if > it does, it will use that, because it is more versatile and less error prone > for function tracing. > > Starting with v4.19, the minimum gcc supported to build the Linux kernel, > was raised to version 4.6. That also happens to be the first gcc version to > support -mfentry. Since on x86, using gcc versions from 4.6 and beyond will > unconditionally enable the -mfentry, it will no longer use mcount as the > method for inserting calls into the C functions of the kernel. This means > that there is no point in continuing to maintain mcount in x86. > > Remove support for using mcount. This makes the code less complex, and will > also allow it to be simplified in the future. > > Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
