Re: [PATCH 6/9] LoongArch: modules/ftrace: Initialize PLT at load time

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On 2022/8/19 下午6:43, Jinyang He wrote:
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@xxxxxxxxxxx>
---
  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.

Hi. Jinyang

Yes, the effect is the same.
I will modify it to lu12iw in V2, which can be consistent with the user's plt style.

Thanks,
- Qing


      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.

Yes, Should return module_init_ftrace_plt(hdr, sechdrs, mod) here.

Thanks,
-Qing
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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