[RFC PATCH 24/32] x86/ftrace: Enable HAVE_FUNCTION_GRAPH_FREGS

Masami Hiramatsu (Google)
2023-11-05T16:11:27Z

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Support HAVE_FUNCTION_GRAPH_FREGS on x86-64, which saves ftrace_regs
on the stack in ftrace_graph return trampoline so that the callbacks
can access registers via ftrace_regs APIs.

Note that this only recovers 'rax' and 'rdx' registers because other
registers are not used anymore and recovered by caller. 'rax' and
'rdx' will be used for passing the return value.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
arch/x86/Kconfig | 3 ++-
arch/x86/kernel/ftrace_64.S | 30 ++++++++++++++++++++++--------
2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 66bfabae8814..4b4c2f9d67da 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -219,7 +219,8 @@ config X86
select HAVE_FAST_GUP
select HAVE_FENTRY if X86_64 || DYNAMIC_FTRACE
select HAVE_FTRACE_MCOUNT_RECORD
- select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
+ select HAVE_FUNCTION_GRAPH_FREGS if HAVE_DYNAMIC_FTRACE_WITH_ARGS
+ select HAVE_FUNCTION_GRAPH_RETVAL if !HAVE_DYNAMIC_FTRACE_WITH_ARGS
select HAVE_FUNCTION_GRAPH_TRACER if X86_32 || (X86_64 && DYNAMIC_FTRACE)
select HAVE_FUNCTION_TRACER
select HAVE_GCC_PLUGINS
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 945cfa5f7239..41351a621753 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -348,21 +348,35 @@ STACK_FRAME_NON_STANDARD_FP(__fentry__)
SYM_CODE_START(return_to_handler)
UNWIND_HINT_UNDEFINED
ANNOTATE_NOENDBR
- subq $24, %rsp
+ /*
+ * We add enough stack to save all regs, but saves only registers
+ * for function params.
+ */
+ subq $(FRAME_SIZE), %rsp
+ movq %rax, RAX(%rsp)
+ movq %rcx, RCX(%rsp)
+ movq %rdx, RDX(%rsp)
+ movq %rsi, RSI(%rsp)
+ movq %rdi, RDI(%rsp)
+ movq %r8, R8(%rsp)
+ movq %r9, R9(%rsp)
+ movq $0, ORIG_RAX(%rsp)
+ movq %rbp, RBP(%rsp)

- /* Save the return values */
- movq %rax, (%rsp)
- movq %rdx, 8(%rsp)
- movq %rbp, 16(%rsp)
movq %rsp, %rdi

call ftrace_return_to_handler

movq %rax, %rdi
- movq 8(%rsp), %rdx
- movq (%rsp), %rax

- addq $24, %rsp
+ /*
+ * Restore only rax and rdx because other registers are not used
+ * for return value nor callee saved. Caller will reuse/recover it.
+ */
+ movq RDX(%rsp), %rdx
+ movq RAX(%rsp), %rax
+
+ addq $(FRAME_SIZE), %rsp
/*
* Jump back to the old return address. This cannot be JMP_NOSPEC rdi
* since IBT would demand that contain ENDBR, which simply isn't so for