On Tue, Nov 18, 2025 at 08:36:30PM +0800, Menglong Dong wrote: > Implement the DYNAMIC_FTRACE_WITH_JMP for x86_64. In ftrace_call_replace, > we will use JMP32_INSN_OPCODE instead of CALL_INSN_OPCODE if the address > should use "jmp". > > Meanwhile, adjust the direct call in the ftrace_regs_caller. The RSB is > balanced in the "jmp" mode. Take the function "foo" for example: > > original_caller: > call foo -> foo: > call fentry -> fentry: > [do ftrace callbacks ] > move tramp_addr to stack > RET -> tramp_addr > tramp_addr: > [..] > call foo_body -> foo_body: > [..] > RET -> back to tramp_addr > [..] > RET -> back to original_caller > > Signed-off-by: Menglong Dong <[email protected]> > --- > arch/x86/Kconfig | 1 + > arch/x86/kernel/ftrace.c | 7 ++++++- > arch/x86/kernel/ftrace_64.S | 12 +++++++++++- > 3 files changed, 18 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index fa3b616af03a..462250a20311 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -230,6 +230,7 @@ config X86 > select HAVE_DYNAMIC_FTRACE_WITH_ARGS if X86_64 > select HAVE_FTRACE_REGS_HAVING_PT_REGS if X86_64 > select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS > + select HAVE_DYNAMIC_FTRACE_WITH_JMP if X86_64 > select HAVE_SAMPLE_FTRACE_DIRECT if X86_64 > select HAVE_SAMPLE_FTRACE_DIRECT_MULTI if X86_64 > select HAVE_EBPF_JIT > diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c > index 4450acec9390..0543b57f54ee 100644 > --- a/arch/x86/kernel/ftrace.c > +++ b/arch/x86/kernel/ftrace.c > @@ -74,7 +74,12 @@ static const char *ftrace_call_replace(unsigned long ip, > unsigned long addr) > * No need to translate into a callthunk. The trampoline does > * the depth accounting itself. > */ > - return text_gen_insn(CALL_INSN_OPCODE, (void *)ip, (void *)addr); > + if (ftrace_is_jmp(addr)) { > + addr = ftrace_jmp_get(addr); > + return text_gen_insn(JMP32_INSN_OPCODE, (void *)ip, (void > *)addr); > + } else { > + return text_gen_insn(CALL_INSN_OPCODE, (void *)ip, (void > *)addr); > + } > } > > static int ftrace_verify_code(unsigned long ip, const char *old_code) > diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S > index 823dbdd0eb41..a132608265f6 100644 > --- a/arch/x86/kernel/ftrace_64.S > +++ b/arch/x86/kernel/ftrace_64.S > @@ -285,8 +285,18 @@ SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL) > ANNOTATE_NOENDBR > RET > > +1: > + testb $1, %al > + jz 2f > + andq $0xfffffffffffffffe, %rax > + movq %rax, MCOUNT_REG_SIZE+8(%rsp) > + restore_mcount_regs > + /* Restore flags */ > + popfq > + RET
is this hunk the reason for the 0x1 jmp-bit you set in the address? I wonder if we introduced new flag in dyn_ftrace::flags for this, then we'd need to have extra ftrace trampoline for jmp ftrace_ops jirka
