Re: [RFC PATCH v3 06/11] powerpc64/ftrace: Move ftrace sequence out of line

Nicholas Piggin
2024-07-01T10:39:13Z

On Fri Jun 21, 2024 at 4:54 AM AEST, Naveen N Rao wrote:
> Function profile sequence on powerpc includes two instructions at the
> beginning of each function:
> mflr r0
> bl ftrace_caller
>
> The call to ftrace_caller() gets nop'ed out during kernel boot and is
> patched in when ftrace is enabled.
>
> Given the sequence, we cannot return from ftrace_caller with 'blr' as we
> need to keep LR and r0 intact. This results in link stack imbalance when

(link stack is IBMese for "return address predictor", if that wasn't
obvious)

> ftrace is enabled. To address that, we would like to use a three
> instruction sequence:
> mflr r0
> bl ftrace_caller
> mtlr r0
>
> Further more, to support DYNAMIC_FTRACE_WITH_CALL_OPS, we need to
> reserve two instruction slots before the function. This results in a
> total of five instruction slots to be reserved for ftrace use on each
> function that is traced.
>
> Move the function profile sequence out-of-line to minimize its impact.
> To do this, we reserve a single nop at function entry using
> -fpatchable-function-entry=1 and add a pass on vmlinux.o to determine

What's the need to do this on vmlinux.o rather than vmlinux? We have
all function syms?

> the total number of functions that can be traced. This is then used to
> generate a .S file reserving the appropriate amount of space for use as
> ftrace stubs, which is built and linked into vmlinux.

An example instruction listing for the "after" case would be nice too.

Is this all ftrace stubs in the one place? And how do you deal with
kernel size exceeding the limit, if so?

>
> On bootup, the stub space is split into separate stubs per function and
> populated with the proper instruction sequence. A pointer to the
> associated stub is maintained in dyn_arch_ftrace.
>
> For modules, space for ftrace stubs is reserved from the generic module
> stub space.
>
> This is restricted to and enabled by default only on 64-bit powerpc.

This is cool.

[...]

> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -568,6 +568,11 @@ config ARCH_USING_PATCHABLE_FUNCTION_ENTRY
> def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh $(CC) -mlittle-endian) if PPC64 && CPU_LITTLE_ENDIAN
> def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh $(CC) -mbig-endian) if PPC64 && CPU_BIG_ENDIAN
>
> +config FTRACE_PFE_OUT_OF_LINE
> + def_bool PPC64 && ARCH_USING_PATCHABLE_FUNCTION_ENTRY
> + depends on PPC64
> + select ARCH_WANTS_PRE_LINK_VMLINUX

This remains powerpc specific? Maybe add a PPC_ prefix to the config
option?

Bikeshed - should PFE be expanded to be consistent with the ARCH_
option?

[...]

> diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
> index 201f9d15430a..9da1da0f87b4 100644
> --- a/arch/powerpc/include/asm/ftrace.h
> +++ b/arch/powerpc/include/asm/ftrace.h
> @@ -26,6 +26,9 @@ unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip,
> struct module;
> struct dyn_ftrace;
> struct dyn_arch_ftrace {
> +#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
> + unsigned long pfe_stub;
> +#endif
> };

Ah, we put something else in here. This is the offset to the
stub? Maybe call it pfe_stub_offset?

[...]

> diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
> index 2cff37b5fd2c..9f3c10307331 100644
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -37,7 +37,8 @@ unsigned long ftrace_call_adjust(unsigned long addr)
> if (addr >= (unsigned long)__exittext_begin && addr < (unsigned long)__exittext_end)
> return 0;
>
> - if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY))
> + if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY) &&
> + !IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE))
> addr += MCOUNT_INSN_SIZE;
>
> return addr;

I don't understand what this is doing acutally (before this patch
even). We still emit one/two patchable intsructions at entry, so
why do we only need to adjust by zero/one instruction here?

> @@ -82,7 +83,7 @@ static inline int ftrace_modify_code(unsigned long ip, ppc_inst_t old, ppc_inst_
> {
> int ret = ftrace_validate_inst(ip, old);
>
> - if (!ret)
> + if (!ret && !ppc_inst_equal(old, new))
> ret = patch_instruction((u32 *)ip, new);
>
> return ret;

Is this leftover debugging stuff or should it be in a different patch?

> @@ -132,11 +133,23 @@ static unsigned long ftrace_lookup_module_stub(unsigned long ip, unsigned long a
> }
> #endif
>
> +static unsigned long ftrace_get_pfe_stub(struct dyn_ftrace *rec)
> +{
> +#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
> + return rec->arch.pfe_stub;
> +#else
> + BUILD_BUG();
> +#endif
> +}
> +
> static int ftrace_get_call_inst(struct dyn_ftrace *rec, unsigned long addr, ppc_inst_t *call_inst)
> {
> unsigned long ip = rec->ip;
> unsigned long stub;
>
> + if (IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE))
> + ip = ftrace_get_pfe_stub(rec) + MCOUNT_INSN_SIZE; /* second instruction in stub */

Maybe put the ip = rec->ip; into an else case here.

[...]

> @@ -155,6 +168,79 @@ static int ftrace_get_call_inst(struct dyn_ftrace *rec, unsigned long addr, ppc_
> return 0;
> }
>
> +static int ftrace_init_pfe_stub(struct module *mod, struct dyn_ftrace *rec)
> +{
> +#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
> + static int pfe_stub_text_index, pfe_stub_inittext_index;
> + int ret = 0, pfe_stub_count, *pfe_stub_index;
> + ppc_inst_t inst;
> + struct ftrace_pfe_stub *pfe_stub, pfe_stub_template = {
> + .insn = {
> + PPC_RAW_MFLR(_R0),
> + PPC_RAW_NOP(), /* bl ftrace_caller */
> + PPC_RAW_MTLR(_R0),
> + PPC_RAW_NOP() /* b rec->ip + 4 */
> + }
> + };
> +
> + WARN_ON(rec->arch.pfe_stub);
> +
> + if (is_kernel_inittext(rec->ip)) {
> + pfe_stub = ftrace_pfe_stub_inittext;
> + pfe_stub_index = &pfe_stub_inittext_index;
> + pfe_stub_count = ftrace_pfe_stub_inittext_count;
> + } else if (is_kernel_text(rec->ip)) {
> + pfe_stub = ftrace_pfe_stub_text;
> + pfe_stub_index = &pfe_stub_text_index;
> + pfe_stub_count = ftrace_pfe_stub_text_count;
> +#ifdef CONFIG_MODULES
> + } else if (mod) {
> + pfe_stub = mod->arch.pfe_stubs;
> + pfe_stub_index = &mod->arch.pfe_stub_index;
> + pfe_stub_count = mod->arch.pfe_stub_count;
> +#endif
> + } else {
> + return -EINVAL;
> + }
> +
> + pfe_stub += (*pfe_stub_index)++;
> +
> + if (WARN_ON(*pfe_stub_index > pfe_stub_count))
> + return -EINVAL;
> +
> + if (!is_offset_in_branch_range((long)rec->ip - (long)&pfe_stub->insn[0]) ||
> + !is_offset_in_branch_range((long)(rec->ip + MCOUNT_INSN_SIZE) - (long)&pfe_stub->insn[3])) {
> + pr_err("%s: ftrace pfe stub out of range (%p -> %p).\n",
> + __func__, (void *)rec->ip, (void *)&pfe_stub->insn[0]);
> + return -EINVAL;
> + }
> +
> + rec->arch.pfe_stub = (unsigned long)&pfe_stub->insn[0];
> +
> + /* bl ftrace_caller */
> + if (mod)
> + /* We can't lookup the module since it is not fully formed yet */

What do you mean here, what would a lookup look like if we could do it?

> + inst = ftrace_create_branch_inst(ftrace_get_pfe_stub(rec) + MCOUNT_INSN_SIZE,
> + mod->arch.tramp, 1);
> + else
> + ret = ftrace_get_call_inst(rec, (unsigned long)ftrace_caller, &inst);
> + pfe_stub_template.insn[1] = ppc_inst_val(inst);
> +
> + /* b rec->ip + 4 */
> + if (!ret && create_branch(&inst, &pfe_stub->insn[3], rec->ip + MCOUNT_INSN_SIZE, 0))
> + return -EINVAL;
> + pfe_stub_template.insn[3] = ppc_inst_val(inst);
> +
> + if (!ret)
> + ret = patch_instructions((u32 *)pfe_stub, (u32 *)&pfe_stub_template,
> + sizeof(pfe_stub_template), false);
> +
> + return ret;
> +#else /* !CONFIG_FTRACE_PFE_OUT_OF_LINE */
> + BUILD_BUG();
> +#endif
> +}
> +
> #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, unsigned long addr)
> {
> @@ -167,18 +253,29 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, unsigned
> int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> {
> ppc_inst_t old, new;
> - int ret;
> + unsigned long ip = rec->ip;
> + int ret = 0;
>
> /* This can only ever be called during module load */
> - if (WARN_ON(!IS_ENABLED(CONFIG_MODULES) || core_kernel_text(rec->ip)))
> + if (WARN_ON(!IS_ENABLED(CONFIG_MODULES) || core_kernel_text(ip)))
> return -EINVAL;
>
> old = ppc_inst(PPC_RAW_NOP());
> - ret = ftrace_get_call_inst(rec, addr, &new);
> - if (ret)
> - return ret;
> + if (IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE)) {
> + ip = ftrace_get_pfe_stub(rec) + MCOUNT_INSN_SIZE; /* second instruction in stub */
> + ret = ftrace_get_call_inst(rec, (unsigned long)ftrace_caller, &old);
> + }
>
> - return ftrace_modify_code(rec->ip, old, new);
> + ret |= ftrace_get_call_inst(rec, addr, &new);
> +
> + if (!ret)
> + ret = ftrace_modify_code(ip, old, new);
> +
> + if (!ret && IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE))
> + ret = ftrace_modify_code(rec->ip, ppc_inst(PPC_RAW_NOP()),
> + ppc_inst(PPC_RAW_BRANCH((long)ftrace_get_pfe_stub(rec) - (long)rec->ip)));
> +
> + return ret;
> }
>
> int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)
> @@ -211,6 +308,13 @@ void ftrace_replace_code(int enable)
> new_addr = ftrace_get_addr_new(rec);
> update = ftrace_update_record(rec, enable);
>
> + if (IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE) && update != FTRACE_UPDATE_IGNORE) {
> + ip = ftrace_get_pfe_stub(rec) + MCOUNT_INSN_SIZE;
> + ret = ftrace_get_call_inst(rec, (unsigned long)ftrace_caller, &nop_inst);
> + if (ret)
> + goto out;
> + }
> +
> switch (update) {
> case FTRACE_UPDATE_IGNORE:
> default:
> @@ -235,6 +339,24 @@ void ftrace_replace_code(int enable)
>
> if (!ret)
> ret = ftrace_modify_code(ip, old, new);
> +
> + if (!ret && IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE) &&
> + (update == FTRACE_UPDATE_MAKE_NOP || update == FTRACE_UPDATE_MAKE_CALL)) {
> + /* Update the actual ftrace location */
> + call_inst = ppc_inst(PPC_RAW_BRANCH((long)ftrace_get_pfe_stub(rec) -
> + (long)rec->ip));
> + nop_inst = ppc_inst(PPC_RAW_NOP());
> + ip = rec->ip;
> +
> + if (update == FTRACE_UPDATE_MAKE_NOP)
> + ret = ftrace_modify_code(ip, call_inst, nop_inst);
> + else
> + ret = ftrace_modify_code(ip, nop_inst, call_inst);
> +
> + if (ret)
> + goto out;
> + }
> +
> if (ret)
> goto out;
> }
> @@ -254,7 +376,8 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
> /* Verify instructions surrounding the ftrace location */
> if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY)) {
> /* Expect nops */
> - ret = ftrace_validate_inst(ip - 4, ppc_inst(PPC_RAW_NOP()));
> + if (!IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE))
> + ret = ftrace_validate_inst(ip - 4, ppc_inst(PPC_RAW_NOP()));
> if (!ret)
> ret = ftrace_validate_inst(ip, ppc_inst(PPC_RAW_NOP()));
> } else if (IS_ENABLED(CONFIG_PPC32)) {
> @@ -278,6 +401,10 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
> if (ret)
> return ret;
>
> + /* Set up out-of-line stub */
> + if (IS_ENABLED(CONFIG_FTRACE_PFE_OUT_OF_LINE))
> + return ftrace_init_pfe_stub(mod, rec);
> +
> /* Nop-out the ftrace location */
> new = ppc_inst(PPC_RAW_NOP());
> addr = MCOUNT_ADDR;
> diff --git a/arch/powerpc/kernel/trace/ftrace_entry.S b/arch/powerpc/kernel/trace/ftrace_entry.S
> index 244a1c7bb1e8..b1cbef24f18f 100644
> --- a/arch/powerpc/kernel/trace/ftrace_entry.S
> +++ b/arch/powerpc/kernel/trace/ftrace_entry.S
> @@ -78,10 +78,6 @@
>
> /* Get the _mcount() call site out of LR */
> mflr r7
> - /* Save it as pt_regs->nip */
> - PPC_STL r7, _NIP(r1)
> - /* Also save it in B's stackframe header for proper unwind */
> - PPC_STL r7, LRSAVE+SWITCH_FRAME_SIZE(r1)
> /* Save the read LR in pt_regs->link */
> PPC_STL r0, _LINK(r1)
>
> @@ -96,16 +92,6 @@
> lwz r5,function_trace_op@l(r3)
> #endif
>
> -#ifdef CONFIG_LIVEPATCH_64
> - mr r14, r7 /* remember old NIP */
> -#endif
> -
> - /* Calculate ip from nip-4 into r3 for call below */
> - subi r3, r7, MCOUNT_INSN_SIZE
> -
> - /* Put the original return address in r4 as parent_ip */
> - mr r4, r0
> -
> /* Save special regs */
> PPC_STL r8, _MSR(r1)
> .if \allregs == 1
> @@ -114,17 +100,64 @@
> PPC_STL r11, _CCR(r1)
> .endif
>
> +#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
> + /* Save our real return address locally for return */
> + PPC_STL r7, STACK_INT_FRAME_MARKER(r1)

Hmm, should you be using STACK_INT_FRAME_MARKER in a
non-INT_FRAME? I actually wanted to turn the int marker
into a 4 byte word and move it into a reserved space in
the frame too. Could it go in pt_regs somewhere?

> + /*
> + * We want the ftrace location in the function, but our lr (in r7)
> + * points at the 'mtlr r0' instruction in the out of line stub. To
> + * recover the ftrace location, we read the branch instruction in the
> + * stub, and adjust our lr by the branch offset.
> + */
> + lwz r8, MCOUNT_INSN_SIZE(r7)
> + slwi r8, r8, 6
> + srawi r8, r8, 6
> + add r3, r7, r8

Clever. Maybe a comment in ftrace_init_pfe_stub() that says to
keep that last instruction in synch with this?

> + /*
> + * Override our nip to point past the branch in the original function.
> + * This allows reliable stack trace and the ftrace stack tracer to work as-is.
> + */
> + add r7, r3, MCOUNT_INSN_SIZE
> +#else
> + /* Calculate ip from nip-4 into r3 for call below */
> + subi r3, r7, MCOUNT_INSN_SIZE
> +#endif
> +
> + /* Save NIP as pt_regs->nip */
> + PPC_STL r7, _NIP(r1)
> + /* Also save it in B's stackframe header for proper unwind */
> + PPC_STL r7, LRSAVE+SWITCH_FRAME_SIZE(r1)
> +#ifdef CONFIG_LIVEPATCH_64
> + mr r14, r7 /* remember old NIP */
> +#endif
> +
> + /* Put the original return address in r4 as parent_ip */
> + mr r4, r0
> +
> /* Load &pt_regs in r6 for call below */
> addi r6, r1, STACK_INT_FRAME_REGS
> .endm
>
> .macro ftrace_regs_exit allregs
> +#ifndef CONFIG_FTRACE_PFE_OUT_OF_LINE
> /* Load ctr with the possibly modified NIP */
> PPC_LL r3, _NIP(r1)
> mtctr r3
>
> #ifdef CONFIG_LIVEPATCH_64
> cmpd r14, r3 /* has NIP been altered? */
> +#endif
> +#else /* !CONFIG_FTRACE_PFE_OUT_OF_LINE */
> +#ifdef CONFIG_LIVEPATCH_64
> + /* Load ctr with the possibly modified NIP */

Comment doesn't apply to this leg of the ifdef AFAIKS.
We load the original NIP into LR, and set CR0 for
livepatch branch.

> + PPC_LL r3, _NIP(r1)
> +
> + cmpd r14, r3 /* has NIP been altered? */
> + bne- 1f
> +#endif
> +
> + PPC_LL r3, STACK_INT_FRAME_MARKER(r1)
> +1: mtlr r3
> #endif
>
> /* Restore gprs */
> @@ -139,7 +172,9 @@
>
> /* Restore possibly modified LR */
> PPC_LL r0, _LINK(r1)
> +#ifndef CONFIG_FTRACE_PFE_OUT_OF_LINE
> mtlr r0
> +#endif
>
> #ifdef CONFIG_PPC64
> /* Restore callee's TOC */
> @@ -153,7 +188,12 @@
> /* Based on the cmpd above, if the NIP was altered handle livepatch */
> bne- livepatch_handler
> #endif
> - bctr /* jump after _mcount site */
> + /* jump after _mcount site */
> +#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
> + blr
> +#else
> + bctr
> +#endif

Here is the crux of it all, we return here with a blr that matches
the return address of the bl which it was called with, so the CPU
can predict it.

I think it would be worth a comment here to explain why you go to
so much effort to add the case that uses LR here. Because the out
of line stub itself could pretty well have the same calling convention
as the original mcount.

Actually that's a thought too. Could you split this patch in two?
First just the patch to add the out of line call but use the same
calling convention as mprofile-kernel. Second which changes it to
use the balanced call/return. Would that be a lot of extra work?

> .endm
>
> _GLOBAL(ftrace_regs_caller)
> @@ -177,6 +217,11 @@ _GLOBAL(ftrace_stub)
>
> #ifdef CONFIG_PPC64
> ftrace_no_trace:
> +#ifdef CONFIG_FTRACE_PFE_OUT_OF_LINE
> + REST_GPR(3, r1)
> + addi r1, r1, SWITCH_FRAME_SIZE+STACK_FRAME_MIN_SIZE
> + blr
> +#else
> mflr r3
> mtctr r3
> REST_GPR(3, r1)
> @@ -184,6 +229,7 @@ ftrace_no_trace:
> mtlr r0
> bctr
> #endif
> +#endif
>
> #ifdef CONFIG_LIVEPATCH_64
> /*
> @@ -196,9 +242,9 @@ ftrace_no_trace:
> *
> * On entry:
> * - we have no stack frame and can not allocate one
> - * - LR points back to the original caller (in A)
> - * - CTR holds the new NIP in C
> - * - r0, r11 & r12 are free
> + * - LR/r0 points back to the original caller (in A)
> + * - CTR/LR holds the new NIP in C
> + * - r11 & r12 are free

Could you explain the added case here, e.g.,

On entry, depending on CONFIG_FTRACE_PFE_OUT_OF_LINE (=n/=y)

> */
> livepatch_handler:
> ld r12, PACA_THREAD_INFO(r13)
> @@ -208,18 +254,23 @@ livepatch_handler:
> addi r11, r11, 24
> std r11, TI_livepatch_sp(r12)
>
> - /* Save toc & real LR on livepatch stack */
> - std r2, -24(r11)
> - mflr r12
> - std r12, -16(r11)
> -
> /* Store stack end marker */
> lis r12, STACK_END_MAGIC@h
> ori r12, r12, STACK_END_MAGIC@l
> std r12, -8(r11)
>
> - /* Put ctr in r12 for global entry and branch there */
> + /* Save toc & real LR on livepatch stack */
> + std r2, -24(r11)
> +#ifndef CONFIG_FTRACE_PFE_OUT_OF_LINE
> + mflr r12
> + std r12, -16(r11)
> mfctr r12
> +#else
> + std r0, -16(r11)
> + mflr r12
> + /* Put ctr in r12 for global entry and branch there */
> + mtctr r12
> +#endif
> bctrl
>
> /*
> diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
> index f420df7888a7..0aef9959f2cd 100644
> --- a/arch/powerpc/kernel/vmlinux.lds.S
> +++ b/arch/powerpc/kernel/vmlinux.lds.S
> @@ -267,14 +267,13 @@ SECTIONS
> .init.text : AT(ADDR(.init.text) - LOAD_OFFSET) {
> _sinittext = .;
> INIT_TEXT
> -
> + *(.tramp.ftrace.init);
> /*
> *.init.text might be RO so we must ensure this section ends on
> * a page boundary.
> */
> . = ALIGN(PAGE_SIZE);
> _einittext = .;
> - *(.tramp.ftrace.init);
> } :text
>
> /* .exit.text is discarded at runtime, not link time,

Why this change?

> diff --git a/arch/powerpc/tools/Makefile b/arch/powerpc/tools/Makefile
> new file mode 100644
> index 000000000000..9e2ba9a85baa
> --- /dev/null
> +++ b/arch/powerpc/tools/Makefile
> @@ -0,0 +1,10 @@
> +# SPDX-License-Identifier: GPL-2.0-or-later
> +
> +quiet_cmd_gen_ftrace_pfe_stubs = FTRACE $@
> + cmd_gen_ftrace_pfe_stubs = $< $(objtree)/vmlinux.o $@
> +
> +targets += .arch.vmlinux.o
> +.arch.vmlinux.o: $(srctree)/arch/powerpc/tools/gen-ftrace-pfe-stubs.sh $(objtree)/vmlinux.o FORCE
> + $(call if_changed,gen_ftrace_pfe_stubs)
> +
> +clean-files += $(objtree)/.arch.vmlinux.S $(objtree)/.arch.vmlinux.o
> diff --git a/arch/powerpc/tools/gen-ftrace-pfe-stubs.sh b/arch/powerpc/tools/gen-ftrace-pfe-stubs.sh
> new file mode 100755
> index 000000000000..ec95e99aff14
> --- /dev/null
> +++ b/arch/powerpc/tools/gen-ftrace-pfe-stubs.sh
> @@ -0,0 +1,48 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0-or-later
> +
> +# Error out on error
> +set -e
> +
> +is_enabled() {
> + grep -q "^$1=y" include/config/auto.conf
> +}
> +
> +vmlinux_o=${1}
> +arch_vmlinux_o=${2}
> +arch_vmlinux_S=$(dirname ${arch_vmlinux_o})/$(basename ${arch_vmlinux_o} .o).S
> +
> +RELOCATION=R_PPC64_ADDR64
> +if is_enabled CONFIG_PPC32; then
> + RELOCATION=R_PPC_ADDR32
> +fi

Started PPC32 support?

> +
> +num_pfe_stubs_text=$(${CROSS_COMPILE}objdump -r -j __patchable_function_entries ${vmlinux_o} |
> + grep -v ".init.text" | grep "${RELOCATION}" | wc -l)
> +num_pfe_stubs_inittext=$(${CROSS_COMPILE}objdump -r -j __patchable_function_entries ${vmlinux_o} |
> + grep ".init.text" | grep "${RELOCATION}" | wc -l)
> +
> +cat > ${arch_vmlinux_S} <<EOF
> +#include <asm/asm-offsets.h>
> +#include <linux/linkage.h>
> +
> +.pushsection .tramp.ftrace.text,"aw"
> +SYM_DATA(ftrace_pfe_stub_text_count, .long ${num_pfe_stubs_text})
> +
> +SYM_CODE_START(ftrace_pfe_stub_text)
> + .space ${num_pfe_stubs_text} * FTRACE_PFE_STUB_SIZE
> +SYM_CODE_END(ftrace_pfe_stub_text)
> +.popsection
> +
> +.pushsection .tramp.ftrace.init,"aw"
> +SYM_DATA(ftrace_pfe_stub_inittext_count, .long ${num_pfe_stubs_inittext})
> +
> +SYM_CODE_START(ftrace_pfe_stub_inittext)
> + .space ${num_pfe_stubs_inittext} * FTRACE_PFE_STUB_SIZE
> +SYM_CODE_END(ftrace_pfe_stub_inittext)
> +.popsection
> +EOF
> +
> +${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS} \
> + ${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} \
> + -c -o ${arch_vmlinux_o} ${arch_vmlinux_S}

Looking pretty good. I don't know the livepatch stuff well though.

Thanks,
Nick