On 2025/11/19 06:01, Jiri Olsa wrote: > 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?
Exactly! > > 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 We don't introduce new dyn_ftrace::flags. I tried to introduce FTRACE_FL_JMP and FTRACE_FL_JMP_EN for this propose before I added the jmp-bit to the address. It's hard to do it this way. First, we need to introduce a ftrace_regs_jmp_caller, which will be used for the "jmp" mode. However, it's difficult when we need to change a call_address to jmp_address in __modify_ftrace_direct(), as it will change the "entry->direct" directly. And maybe we need reconstruct the direct call to implement it this way. I were almost giving up before I thought the jmp-bit, which allow us the update the address from call mode to jmp mode atomically. Thanks! Menglong Dong > > jirka > >
