x86-64: fix thread tracing (61d42cf4) · Commits · Wenxi XU / zephyr

The current instrumentation point for CONFIG_TRACING added in PR #28512 had two problems: - If userspace and KPTI are enabled, the tracing point is simply never run if we are resuming a user thread as the z_x86_trampoline_to_user function is jumped to and calls 'iret' from there - Only %rdi is being saved. However, at that location, *all* caller-saved registers are in use as they contain the resumed thread's context Simplest solution is to move this up near where we update page tables. The #ifdefs are used to make sure we don't push/pop %rdi more than once. At that point in the code only %rdi is in use among the volatile registers. Signed-off-by:

Andrew Boie <andrew.p.boie@intel.com>

arch/x86/core/intel64/locore.S

+10 −10

Original line number	Diff line number	Diff line
		@@ -324,17 +324,23 @@ z_x86_switch:
		*/

		__resume:
		#ifdef CONFIG_USERSPACE
		#ifndef CONFIG_X86_KPTI
		#if (!defined(CONFIG_X86_KPTI) && defined(CONFIG_USERSPACE)) \
		\|\| defined(CONFIG_TRACING)
		pushq %rdi /* Caller-saved, stash it */
		#if !defined(CONFIG_X86_KPTI) && defined(CONFIG_USERSPACE)
		/* If KPTI is enabled we're always on the kernel's page tables in
		* this context and the appropriate page table switch takes place
		* when trampolining back to user mode
		*/
		pushq %rdi /* Caller-saved, stash it */
		call z_x86_swap_update_page_tables
		#endif
		#ifdef CONFIG_TRACING
		call sys_trace_thread_switched_in
		#endif
		popq %rdi
		#endif /* CONFIG_X86_KPTI */
		#endif /* (!CONFIG_X86_KPTI && CONFIG_USERSPACE) \|\| CONFIG_TRACING */

		#ifdef CONFIG_USERSPACE
		/* Set up exception return stack frame */
		pushq _thread_offset_to_ss(%rdi) /* SS */
		#else
		@@ -402,12 +408,6 @@ __resume:
		/* swapgs variant of Spectre V1. Disable speculation past this point */
		lfence
		#endif /* CONFIG_X86_BOUNDS_CHECK_BYPASS_MITIGATION */

		#ifdef CONFIG_TRACING
		pushq %rdi
		call sys_trace_thread_switched_in
		popq %rdi
		#endif
		iretq

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