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SubjectRe: [PATCH 6/9] LoongArch: modules/ftrace: Initialize PLT at load time
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On 2022/8/19 16:16, Qing Zhang wrote:

> To Implement ftrace trampiones through plt entry.
>
> Tested by forcing ftrace_make_call() to use the module PLT, and then
> loading up a module after setting up ftrace with:
>
> | echo ":mod:<module-name>" > set_ftrace_filter;
> | echo function > current_tracer;
> | modprobe <module-name>
>
> Since FTRACE_ADDR/FTRACE_REGS_ADDR is only defined when CONFIG_DYNAMIC_FTRACE
> is selected, we wrap its use along with most of module_init_ftrace_plt() with
> ifdeffery rather than using IS_ENABLED().
>
> Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
> ---
> arch/loongarch/include/asm/ftrace.h | 4 ++
> arch/loongarch/include/asm/inst.h | 2 +
> arch/loongarch/include/asm/module.h | 14 +++--
> arch/loongarch/include/asm/module.lds.h | 1 +
> arch/loongarch/kernel/ftrace_dyn.c | 79 +++++++++++++++++++++++++
> arch/loongarch/kernel/inst.c | 12 ++++
> arch/loongarch/kernel/module-sections.c | 11 ++++
> arch/loongarch/kernel/module.c | 48 +++++++++++++++
> 8 files changed, 166 insertions(+), 5 deletions(-)
[...]
> @@ -36,14 +39,15 @@ Elf_Addr module_emit_plt_entry(struct module *mod, unsigned long val);
>
> static inline struct plt_entry emit_plt_entry(unsigned long val)
> {
> - u32 lu12iw, lu32id, lu52id, jirl;
> + u32 addu16id, lu32id, lu52id, jirl;
>
> - lu12iw = (lu12iw_op << 25 | (((val >> 12) & 0xfffff) << 5) | LOONGARCH_GPR_T1);
> + addu16id = larch_insn_gen_addu16id(LOONGARCH_GPR_T1, LOONGARCH_GPR_ZERO,
> + ADDR_IMM(val, ADDU16ID));

Hi, Qing,

Why change lu12iw to addu16id? They have same effect here.


> lu32id = larch_insn_gen_lu32id(LOONGARCH_GPR_T1, ADDR_IMM(val, LU32ID));
> lu52id = larch_insn_gen_lu52id(LOONGARCH_GPR_T1, LOONGARCH_GPR_T1, ADDR_IMM(val, LU52ID));
> - jirl = larch_insn_gen_jirl(0, LOONGARCH_GPR_T1, 0, (val & 0xfff));
> + jirl = larch_insn_gen_jirl(0, LOONGARCH_GPR_T1, 0, (val & 0xffff));
>
> - return (struct plt_entry) { lu12iw, lu32id, lu52id, jirl };
> + return (struct plt_entry) { addu16id, lu32id, lu52id, jirl };
> }
[...]
> +static int module_init_ftrace_plt(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
> + struct module *mod)
> +{
> +#ifdef CONFIG_DYNAMIC_FTRACE
> + const Elf_Shdr *s;
> + struct plt_entry *ftrace_plts;
> +
> + s = find_section(hdr, sechdrs, ".ftrace_trampoline");
> + if (!s)
> + return -ENOEXEC;

Return value is not used later, may we do something or drop returning value.

Thanks,

Jinyang

> +
> + ftrace_plts = (void *)s->sh_addr;
> +
> + ftrace_plts[FTRACE_PLT_IDX] = emit_plt_entry(FTRACE_ADDR);
> +
> + if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
> + ftrace_plts[FTRACE_REGS_PLT_IDX] = emit_plt_entry(FTRACE_REGS_ADDR);
> +
> + mod->arch.ftrace_trampolines = ftrace_plts;
> +#endif
> + return 0;
> +}
> +
> +int module_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs, struct module *mod)
> +{
> + module_init_ftrace_plt(hdr, sechdrs, mod);
> +
> + return 0;
> +}

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