linux-dev/arch/riscv/kernel/mcount-dyn.S, branch linus/master

riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT

2021-01-14T23:09:05Z

This patch changes the current detour mechanism of dynamic ftrace which has been discussed during LPC 2020 RISCV-MC [1]. Before the patch, we used mcount for detour: : addi sp,sp,-16 sd ra,8(sp) sd s0,0(sp) addi s0,sp,16 mv a5,ra mv a0,a5 auipc ra,0x0 -> nop jalr -296(ra) <_mcount@plt> ->nop ... After the patch, we use nop call site area for detour: : nop -> REG_S ra, -SZREG(sp) nop -> auipc ra, 0x? nop -> jalr ?(ra) nop -> REG_L ra, -SZREG(sp) ... The mcount mechanism is mixed with gcc function prologue which is not very clear. The patchable function entry just put 16 bytes nop before the front of the function prologue which could be filled with a separated detour mechanism. [1] https://www.linuxplumbersconf.org/event/7/contributions/807/ Signed-off-by: Guo Ren Signed-off-by: Palmer Dabbelt

riscv/ftrace: Add DYNAMIC_FTRACE_WITH_REGS support

2018-04-03T02:59:13Z

Cc: Greentime Hu Signed-off-by: Alan Kao Signed-off-by: Palmer Dabbelt

riscv/ftrace: Add ARCH_SUPPORTS_FTRACE_OPS support

2018-04-03T02:59:12Z

Cc: Greentime Hu Signed-off-by: Alan Kao Signed-off-by: Palmer Dabbelt

riscv/ftrace: Add dynamic function graph tracer support

2018-04-03T02:59:12Z

Once the function_graph tracer is enabled, a filtered function has the following call sequence: * ftracer_caller ==> on/off by ftrace_make_call/ftrace_make_nop * ftrace_graph_caller * ftrace_graph_call ==> on/off by ftrace_en/disable_ftrace_graph_caller * prepare_ftrace_return Considering the following DYNAMIC_FTRACE_WITH_REGS feature, it would be more extendable to have a ftrace_graph_caller function, instead of calling prepare_ftrace_return directly in ftrace_caller. Cc: Greentime Hu Signed-off-by: Alan Kao Signed-off-by: Palmer Dabbelt

riscv/ftrace: Add dynamic function tracer support

2018-04-03T02:59:12Z

We now have dynamic ftrace with the following added items: * ftrace_make_call, ftrace_make_nop (in kernel/ftrace.c) The two functions turn each recorded call site of filtered functions into a call to ftrace_caller or nops * ftracce_update_ftrace_func (in kernel/ftrace.c) turns the nops at ftrace_call into a call to a generic entry for function tracers. * ftrace_caller (in kernel/mcount-dyn.S) The entry where each _mcount call sites calls to once they are filtered to be traced. Also, this patch fixes the semantic problems in mcount.S, which will be treated as only a reference implementation once we have the dynamic ftrace. Cc: Greentime Hu Signed-off-by: Alan Kao Signed-off-by: Palmer Dabbelt