Re: [PATCH v4 5/9] ftrace: Add ftrace_partial_regs() for converting ftrace_regs to pt_regs
From: Andrii Nakryiko <hidden>
Date: 2023-08-25 21:50:38
Also in:
bpf, lkml
On Wed, Aug 23, 2023 at 8:16 AM Masami Hiramatsu (Google) [off-list ref] wrote:
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From: Masami Hiramatsu (Google) <mhiramat@kernel.org> Add ftrace_partial_regs() which converts the ftrace_regs to pt_regs. If the architecture defines its own ftrace_regs, this copies partial registers to pt_regs and returns it. If not, ftrace_regs is the same as pt_regs and ftrace_partial_regs() will return ftrace_regs::regs. Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Acked-by: Florent Revest <redacted> --- Changes in v3: - Fix to use pt_regs::regs instead of x. - Return ftrace_regs::regs forcibly if HAVE_PT_REGS_COMPAT_FTRACE_REGS=y. - Fix typo. - Fix to copy correct registers to the pt_regs on arm64. Changes in v4: - Change the patch order in the series so that fprobe event can use this. --- arch/arm64/include/asm/ftrace.h | 11 +++++++++++ include/linux/ftrace.h | 17 +++++++++++++++++ 2 files changed, 28 insertions(+)diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h index ab158196480c..5ad24f315d52 100644 --- a/arch/arm64/include/asm/ftrace.h +++ b/arch/arm64/include/asm/ftrace.h@@ -137,6 +137,17 @@ ftrace_override_function_with_return(struct ftrace_regs *fregs) fregs->pc = fregs->lr; } +static __always_inline struct pt_regs * +ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs) +{ + memcpy(regs->regs, fregs->regs, sizeof(u64) * 9); + regs->sp = fregs->sp; + regs->pc = fregs->pc; + regs->regs[29] = fregs->fp; + regs->regs[30] = fregs->lr;
I see that orig_x0 from pt_regs is used on arm64 to get syscall's first parameter. And it seems like this ftrace_regs to pt_regs conversion doesn't touch orig_x0 at all. Is it maintained/preserved somewhere else, or will we lose the ability to get the first syscall's argument? Looking at libbpf's bpf_tracing.h, other than orig_x0, I think all the other registers are still preserved, so this seems to be the only potential problem.
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+ return regs; +} + int ftrace_regs_query_register_offset(const char *name); int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index c0a42d0860b8..a6ed2aa71efc 100644 --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h@@ -165,6 +165,23 @@ static __always_inline struct pt_regs *ftrace_get_regs(struct ftrace_regs *fregs return arch_ftrace_get_regs(fregs); } +#if !defined(CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS) || \ + defined(CONFIG_HAVE_PT_REGS_TO_FTRACE_REGS_CAST) + +static __always_inline struct pt_regs * +ftrace_partial_regs(struct ftrace_regs *fregs, struct pt_regs *regs) +{ + /* + * If CONFIG_HAVE_PT_REGS_TO_FTRACE_REGS_CAST=y, ftrace_regs memory + * layout is the same as pt_regs. So always returns that address. + * Since arch_ftrace_get_regs() will check some members and may return + * NULL, we can not use it. + */ + return &fregs->regs; +} + +#endif /* !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS || CONFIG_HAVE_PT_REGS_TO_FTRACE_REGS_CAST */ + /* * When true, the ftrace_regs_{get,set}_*() functions may be used on fregs. * Note: this can be true even when ftrace_get_regs() cannot provide a pt_regs.