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Message-ID: <CAK7LNASMYLwjyHx+yx_+6uGSuSVNgPR3uX1QHAf1RyKrDhgTAQ@mail.gmail.com>
Date: Sun, 27 Oct 2024 18:17:23 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Hari Bathini <hbathini@...ux.ibm.com>
Cc: linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, bpf@...r.kernel.org,
linux-trace-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
linux-kernel@...r.kernel.org, Michael Ellerman <mpe@...erman.id.au>,
"Naveen N. Rao" <naveen@...nel.org>, Mark Rutland <mark.rutland@....com>,
Daniel Borkmann <daniel@...earbox.net>, Nicholas Piggin <npiggin@...il.com>,
Alexei Starovoitov <ast@...nel.org>, Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>, Andrii Nakryiko <andrii@...nel.org>,
Christophe Leroy <christophe.leroy@...roup.eu>, Vishal Chourasia <vishalc@...ux.ibm.com>,
Mahesh J Salgaonkar <mahesh@...ux.ibm.com>
Subject: Re: [PATCH v6 13/17] powerpc64/ftrace: Support .text larger than 32MB
with out-of-line stubs
On Sat, Oct 19, 2024 at 2:38 AM Hari Bathini <hbathini@...ux.ibm.com> wrote:
>
> From: Naveen N Rao <naveen@...nel.org>
>
> We are restricted to a .text size of ~32MB when using out-of-line
> function profile sequence. Allow this to be extended up to the previous
> limit of ~64MB by reserving space in the middle of .text.
>
> A new config option CONFIG_PPC_FTRACE_OUT_OF_LINE_NUM_RESERVE is
> introduced to specify the number of function stubs that are reserved in
> .text. On boot, ftrace utilizes stubs from this area first before using
> the stub area at the end of .text.
>
> A ppc64le defconfig has ~44k functions that can be traced. A more
> conservative value of 32k functions is chosen as the default value of
> PPC_FTRACE_OUT_OF_LINE_NUM_RESERVE so that we do not allot more space
> than necessary by default. If building a kernel that only has 32k
> trace-able functions, we won't allot any more space at the end of .text
> during the pass on vmlinux.o. Otherwise, only the remaining functions
> get space for stubs at the end of .text. This default value should help
> cover a .text size of ~48MB in total (including space reserved at the
> end of .text which can cover up to 32MB), which should be sufficient for
> most common builds. For a very small kernel build, this can be set to 0.
> Or, this can be bumped up to a larger value to support vmlinux .text
> size up to ~64MB.
>
> Signed-off-by: Naveen N Rao <naveen@...nel.org>
> Signed-off-by: Hari Bathini <hbathini@...ux.ibm.com>
> ---
>
> Changes in v6:
> * Updated with Masahiro's suggestions at
> https://lore.kernel.org/all/CAK7LNAREkj5OQ_HA2H=iV_32qdOcaguCOBKV1j+dJW0YaQh3UA@mail.gmail.com/
>
>
> arch/powerpc/Kconfig | 12 ++++++++++++
> arch/powerpc/include/asm/ftrace.h | 6 ++++--
> arch/powerpc/kernel/trace/ftrace.c | 21 +++++++++++++++++----
> arch/powerpc/kernel/trace/ftrace_entry.S | 8 ++++++++
> arch/powerpc/tools/Makefile | 3 ++-
> arch/powerpc/tools/ftrace-gen-ool-stubs.sh | 19 +++++++++++++------
> 6 files changed, 56 insertions(+), 13 deletions(-)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 26e3060e44f4..2e347f682c15 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -573,6 +573,18 @@ config PPC_FTRACE_OUT_OF_LINE
> def_bool PPC64 && ARCH_USING_PATCHABLE_FUNCTION_ENTRY
> select ARCH_WANTS_PRE_LINK_VMLINUX
>
> +config PPC_FTRACE_OUT_OF_LINE_NUM_RESERVE
> + int "Number of ftrace out-of-line stubs to reserve within .text"
> + depends on PPC_FTRACE_OUT_OF_LINE
> + default 32768
> + help
> + Number of stubs to reserve for use by ftrace. This space is
> + reserved within .text, and is distinct from any additional space
> + added at the end of .text before the final vmlinux link. Set to
> + zero to have stubs only be generated at the end of vmlinux (only
> + if the size of vmlinux is less than 32MB). Set to a higher value
> + if building vmlinux larger than 48MB.
> +
> config HOTPLUG_CPU
> bool "Support for enabling/disabling CPUs"
> depends on SMP && (PPC_PSERIES || \
> diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
> index bdbafc668b20..28f3590ca780 100644
> --- a/arch/powerpc/include/asm/ftrace.h
> +++ b/arch/powerpc/include/asm/ftrace.h
> @@ -138,8 +138,10 @@ extern unsigned int ftrace_tramp_text[], ftrace_tramp_init[];
> struct ftrace_ool_stub {
> u32 insn[4];
> };
> -extern struct ftrace_ool_stub ftrace_ool_stub_text_end[], ftrace_ool_stub_inittext[];
> -extern unsigned int ftrace_ool_stub_text_end_count, ftrace_ool_stub_inittext_count;
> +extern struct ftrace_ool_stub ftrace_ool_stub_text_end[], ftrace_ool_stub_text[],
> + ftrace_ool_stub_inittext[];
> +extern unsigned int ftrace_ool_stub_text_end_count, ftrace_ool_stub_text_count,
> + ftrace_ool_stub_inittext_count;
> #endif
> void ftrace_free_init_tramp(void);
> unsigned long ftrace_call_adjust(unsigned long addr);
> diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
> index 1fee074388cc..bee2c54a8c04 100644
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -168,7 +168,7 @@ static int ftrace_get_call_inst(struct dyn_ftrace *rec, unsigned long addr, ppc_
> static int ftrace_init_ool_stub(struct module *mod, struct dyn_ftrace *rec)
> {
> #ifdef CONFIG_PPC_FTRACE_OUT_OF_LINE
> - static int ool_stub_text_end_index, ool_stub_inittext_index;
> + static int ool_stub_text_index, ool_stub_text_end_index, ool_stub_inittext_index;
> int ret = 0, ool_stub_count, *ool_stub_index;
> ppc_inst_t inst;
> /*
> @@ -191,9 +191,22 @@ static int ftrace_init_ool_stub(struct module *mod, struct dyn_ftrace *rec)
> ool_stub_index = &ool_stub_inittext_index;
> ool_stub_count = ftrace_ool_stub_inittext_count;
> } else if (is_kernel_text(rec->ip)) {
> - ool_stub = ftrace_ool_stub_text_end;
> - ool_stub_index = &ool_stub_text_end_index;
> - ool_stub_count = ftrace_ool_stub_text_end_count;
> + /*
> + * ftrace records are sorted, so we first use up the stub area within .text
> + * (ftrace_ool_stub_text) before using the area at the end of .text
> + * (ftrace_ool_stub_text_end), unless the stub is out of range of the record.
> + */
> + if (ool_stub_text_index >= ftrace_ool_stub_text_count ||
> + !is_offset_in_branch_range((long)rec->ip -
> + (long)&ftrace_ool_stub_text[ool_stub_text_index])) {
> + ool_stub = ftrace_ool_stub_text_end;
> + ool_stub_index = &ool_stub_text_end_index;
> + ool_stub_count = ftrace_ool_stub_text_end_count;
> + } else {
> + ool_stub = ftrace_ool_stub_text;
> + ool_stub_index = &ool_stub_text_index;
> + ool_stub_count = ftrace_ool_stub_text_count;
> + }
> #ifdef CONFIG_MODULES
> } else if (mod) {
> ool_stub = mod->arch.ool_stubs;
> diff --git a/arch/powerpc/kernel/trace/ftrace_entry.S b/arch/powerpc/kernel/trace/ftrace_entry.S
> index 5b2fc6483dce..a6bf7f841040 100644
> --- a/arch/powerpc/kernel/trace/ftrace_entry.S
> +++ b/arch/powerpc/kernel/trace/ftrace_entry.S
> @@ -374,6 +374,14 @@ _GLOBAL(return_to_handler)
> blr
> #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
>
> +#ifdef CONFIG_PPC_FTRACE_OUT_OF_LINE
> +SYM_DATA(ftrace_ool_stub_text_count, .long CONFIG_PPC_FTRACE_OUT_OF_LINE_NUM_RESERVE)
> +
> +SYM_CODE_START(ftrace_ool_stub_text)
> + .space CONFIG_PPC_FTRACE_OUT_OF_LINE_NUM_RESERVE * FTRACE_OOL_STUB_SIZE
> +SYM_CODE_END(ftrace_ool_stub_text)
> +#endif
> +
> .pushsection ".tramp.ftrace.text","aw",@progbits;
> .globl ftrace_tramp_text
> ftrace_tramp_text:
> diff --git a/arch/powerpc/tools/Makefile b/arch/powerpc/tools/Makefile
> index d2e7ecd5f46f..e1f7afcd9fdf 100644
> --- a/arch/powerpc/tools/Makefile
> +++ b/arch/powerpc/tools/Makefile
> @@ -1,7 +1,8 @@
> # SPDX-License-Identifier: GPL-2.0-or-later
>
> quiet_cmd_gen_ftrace_ool_stubs = GEN $@
> - cmd_gen_ftrace_ool_stubs = $< "$(CONFIG_64BIT)" "$(OBJDUMP)" vmlinux.o $@
> + cmd_gen_ftrace_ool_stubs = $< "$(CONFIG_PPC_FTRACE_OUT_OF_LINE_NUM_RESERVE)" "$(CONFIG_64BIT)" \
> + "$(OBJDUMP)" vmlinux.o $@
>
> $(obj)/vmlinux.arch.S: $(src)/ftrace-gen-ool-stubs.sh vmlinux.o FORCE
> $(call if_changed,gen_ftrace_ool_stubs)
> diff --git a/arch/powerpc/tools/ftrace-gen-ool-stubs.sh b/arch/powerpc/tools/ftrace-gen-ool-stubs.sh
> index 96e1ca5803e4..3ea0f23f2501 100755
> --- a/arch/powerpc/tools/ftrace-gen-ool-stubs.sh
> +++ b/arch/powerpc/tools/ftrace-gen-ool-stubs.sh
> @@ -4,10 +4,11 @@
> # Error out on error
> set -e
>
> -is_64bit="$1"
> -objdump="$2"
> -vmlinux_o="$3"
> -arch_vmlinux_S="$4"
> +num_ool_stubs_text_builtin="$1"
> +is_64bit="$2"
> +objdump="$3"
> +vmlinux_o="$4"
> +arch_vmlinux_S="$5"
>
> RELOCATION=R_PPC64_ADDR64
> if [ -z "$is_64bit" ]; then
> @@ -19,15 +20,21 @@ num_ool_stubs_text=$($objdump -r -j __patchable_function_entries "$vmlinux_o" |
> num_ool_stubs_inittext=$($objdump -r -j __patchable_function_entries "$vmlinux_o" |
> grep ".init.text" | grep -c "$RELOCATION")
>
> +if [ "$num_ool_stubs_text" -gt "$num_ool_stubs_text_builtin" ]; then
> + num_ool_stubs_text_end=$((num_ool_stubs_text - num_ool_stubs_text_builtin))
> +else
> + num_ool_stubs_text_end=0
> +fi
> +
> cat > "$arch_vmlinux_S" <<EOF
> #include <asm/asm-offsets.h>
> #include <linux/linkage.h>
>
> .pushsection .tramp.ftrace.text,"aw"
> -SYM_DATA(ftrace_ool_stub_text_end_count, .long $num_ool_stubs_text)
> +SYM_DATA(ftrace_ool_stub_text_end_count, .long $num_ool_stubs_text_end)
>
> SYM_CODE_START(ftrace_ool_stub_text_end)
> - .space $num_ool_stubs_text * FTRACE_OOL_STUB_SIZE
> + .space $num_ool_stubs_text_end * FTRACE_OOL_STUB_SIZE
> SYM_CODE_END(ftrace_ool_stub_text_end)
> .popsection
I got this warning:
GEN arch/powerpc/tools/vmlinux.arch.S
AS arch/powerpc/tools/vmlinux.arch.o
arch/powerpc/tools/vmlinux.arch.S: Assembler messages:
arch/powerpc/tools/vmlinux.arch.S:9: Warning: .space repeat count is
zero, ignored
--
Best Regards
Masahiro Yamada
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