[PATCH 0/3] powerpc64/ftrace: fixes clang build issues

[PATCH 0/3] powerpc64/ftrace: fixes clang build issues

[Hari Bathini]

Support for -fpatchable-function-entry on ppc64le was added in Clang
with [1]. Faced a couple of issues while building the linux kernel
with Clang though. Patches 1 & 2 address those issues. The last patch
provides workaround to ensure, an open issue [2] in Clang with
-fpatchable-function-entry support, does not impact the linux
ftrace subsystem.

[1] https://github.com/llvm/llvm-project/pull/151569
[2] https://github.com/llvm/llvm-project/issues/163706

Hari Bathini (3):
  powerpc64: make clang cross-build friendly
  powerpc64/ftrace: fix OOL stub count with clang
  powerpc64/ftrace: workaround clang recording GEP in
    __patchable_function_entries

 arch/powerpc/Kconfig                          |  5 ++--
 arch/powerpc/kernel/trace/ftrace.c            | 26 ++++++++++++++++---
 ....sh => check-fpatchable-function-entry.sh} |  0
 arch/powerpc/tools/ftrace-gen-ool-stubs.sh    |  4 +--
 4 files changed, 27 insertions(+), 8 deletions(-)
 rename arch/powerpc/tools/{gcc-check-fpatchable-function-entry.sh => check-fpatchable-function-entry.sh} (100%)

-- 
2.51.1

[PATCH 1/3] powerpc64: make clang cross-build friendly

[Hari Bathini]

ARCH_USING_PATCHABLE_FUNCTION_ENTRY depends on toolchain support for
-fpatchable-function-entry option. The current script that checks
for this support only handles GCC. Rename the script and extend it
to detect support for -fpatchable-function-entry with Clang as well,
allowing clean cross-compilation with Clang toolchains.

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---
 arch/powerpc/Kconfig                                         | 5 +++--
 ...-function-entry.sh => check-fpatchable-function-entry.sh} | 0
 2 files changed, 3 insertions(+), 2 deletions(-)
 rename arch/powerpc/tools/{gcc-check-fpatchable-function-entry.sh => check-fpatchable-function-entry.sh} (100%)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 325c1171894d..dfb62e211c92 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -568,8 +568,9 @@ config ARCH_USING_PATCHABLE_FUNCTION_ENTRY
 	depends on FUNCTION_TRACER && (PPC32 || PPC64_ELF_ABI_V2)
 	depends on $(cc-option,-fpatchable-function-entry=2)
 	def_bool y if PPC32
-	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
+	def_bool $(success,$(srctree)/arch/powerpc/tools/check-fpatchable-function-entry.sh $(CC) -mlittle-endian) if PPC64 && CPU_LITTLE_ENDIAN && CC_IS_GCC
+	def_bool $(success,$(srctree)/arch/powerpc/tools/check-fpatchable-function-entry.sh $(CC) -target ppc64le -mlittle-endian) if PPC64 && CPU_LITTLE_ENDIAN && CC_IS_CLANG
+	def_bool $(success,$(srctree)/arch/powerpc/tools/check-fpatchable-function-entry.sh $(CC) -mbig-endian) if PPC64 && CPU_BIG_ENDIAN
 
 config PPC_FTRACE_OUT_OF_LINE
 	def_bool PPC64 && ARCH_USING_PATCHABLE_FUNCTION_ENTRY
diff --git a/arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh b/arch/powerpc/tools/check-fpatchable-function-entry.sh
similarity index 100%
rename from arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh
rename to arch/powerpc/tools/check-fpatchable-function-entry.sh
-- 
2.51.1

[PATCH 2/3] powerpc64/ftrace: fix OOL stub count with clang

[Hari Bathini]

The total number of out-of-line (OOL) stubs required for function
tracing is determined using the following command:

    $(OBJDUMP) -r -j __patchable_function_entries vmlinux.o

While this works correctly with GNU objdump, llvm-objdump does not
list the expected relocation records for this section. Fix this by
using the -d option and counting R_PPC64_ADDR64 relocation entries.
This works as desired with both objdump and llvm-objdump.

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---
 arch/powerpc/tools/ftrace-gen-ool-stubs.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/tools/ftrace-gen-ool-stubs.sh b/arch/powerpc/tools/ftrace-gen-ool-stubs.sh
index bac186bdf64a..9218d43aeb54 100755
--- a/arch/powerpc/tools/ftrace-gen-ool-stubs.sh
+++ b/arch/powerpc/tools/ftrace-gen-ool-stubs.sh
@@ -15,9 +15,9 @@ if [ -z "$is_64bit" ]; then
 	RELOCATION=R_PPC_ADDR32
 fi
 
-num_ool_stubs_total=$($objdump -r -j __patchable_function_entries "$vmlinux_o" |
+num_ool_stubs_total=$($objdump -r -j __patchable_function_entries -d "$vmlinux_o" |
 		      grep -c "$RELOCATION")
-num_ool_stubs_inittext=$($objdump -r -j __patchable_function_entries "$vmlinux_o" |
+num_ool_stubs_inittext=$($objdump -r -j __patchable_function_entries -d "$vmlinux_o" |
 			 grep -e ".init.text" -e ".text.startup" | grep -c "$RELOCATION")
 num_ool_stubs_text=$((num_ool_stubs_total - num_ool_stubs_inittext))
 
-- 
2.51.1

[PATCH 3/3] powerpc64/ftrace: workaround clang recording GEP in __patchable_function_entries

[Hari Bathini]

Support for -fpatchable-function-entry on ppc64le was added in Clang
with [1]. However, when no prefix NOPs are specified - as is the case
with CONFIG_PPC_FTRACE_OUT_OF_LINE - the first NOP is emitted at LEP,
but Clang records the Global Entry Point (GEP) unlike GCC which does
record the Local Entry Point (LEP). Issue [2] has been raised to align
Clang's behavior with GCC. As a temporary workaround to ensure ftrace
initialization works as expected with Clang, derive the LEP using
ppc_function_entry() for kernel symbols and by looking for the below
module GEP sequence for module addresses, until [2] is resolved:

	ld	r2, -8(r12)
	add	r2, r2, r12

[1] https://github.com/llvm/llvm-project/pull/151569
[2] https://github.com/llvm/llvm-project/issues/163706

Cc: Maryam Moghadas <maryammo@ca.ibm.com>
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---
 arch/powerpc/kernel/trace/ftrace.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index 841d077e2825..1b2f293e7dcb 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -37,11 +37,29 @@ 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) &&
-	    !IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE)) {
-		addr += MCOUNT_INSN_SIZE;
-		if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
+	if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY)) {
+		if (!IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE)) {
 			addr += MCOUNT_INSN_SIZE;
+			if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
+				addr += MCOUNT_INSN_SIZE;
+		} else if (IS_ENABLED(CONFIG_CC_IS_CLANG) && IS_ENABLED(CONFIG_PPC64)) {
+			/*
+			 * addr points to global entry point though the NOP was emitted at local
+			 * entry point due to https://github.com/llvm/llvm-project/issues/163706
+			 * Handle that here with ppc_function_entry() for kernel symbols while
+			 * adjusting module addresses in the else case, by looking for the below
+			 * module global entry point sequence:
+			 *	ld    r2, -8(r12)
+			 *	add   r2, r2, r12
+			 */
+			if (is_kernel_text(addr) || is_kernel_inittext(addr))
+				addr = ppc_function_entry((void *)addr);
+			else if ((ppc_inst_val(ppc_inst_read((u32 *)addr)) ==
+				  PPC_RAW_LD(_R2, _R12, -8)) &&
+				 (ppc_inst_val(ppc_inst_read((u32 *)(addr+4))) ==
+				  PPC_RAW_ADD(_R2, _R2, _R12)))
+				addr += 8;
+		}
 	}
 
 	return addr;
-- 
2.51.1

Re: [PATCH 1/3] powerpc64: make clang cross-build friendly

[Naveen N Rao]

On Sun, Nov 09, 2025 at 02:34:03AM +0530, Hari Bathini wrote:
> ARCH_USING_PATCHABLE_FUNCTION_ENTRY depends on toolchain support for
> -fpatchable-function-entry option. The current script that checks
> for this support only handles GCC. Rename the script and extend it
> to detect support for -fpatchable-function-entry with Clang as well,
> allowing clean cross-compilation with Clang toolchains.
> 
> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
> ---
>  arch/powerpc/Kconfig                                         | 5 +++--
>  ...-function-entry.sh => check-fpatchable-function-entry.sh} | 0
>  2 files changed, 3 insertions(+), 2 deletions(-)
>  rename arch/powerpc/tools/{gcc-check-fpatchable-function-entry.sh => check-fpatchable-function-entry.sh} (100%)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 325c1171894d..dfb62e211c92 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -568,8 +568,9 @@ config ARCH_USING_PATCHABLE_FUNCTION_ENTRY
>  	depends on FUNCTION_TRACER && (PPC32 || PPC64_ELF_ABI_V2)
>  	depends on $(cc-option,-fpatchable-function-entry=2)
>  	def_bool y if PPC32
> -	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
> +	def_bool $(success,$(srctree)/arch/powerpc/tools/check-fpatchable-function-entry.sh $(CC) -mlittle-endian) if PPC64 && CPU_LITTLE_ENDIAN && CC_IS_GCC
> +	def_bool $(success,$(srctree)/arch/powerpc/tools/check-fpatchable-function-entry.sh $(CC) -target ppc64le -mlittle-endian) if PPC64 && CPU_LITTLE_ENDIAN && CC_IS_CLANG

Can you instead pass $(CLANG_FLAGS) to retain the same command across 
gcc/clang?

- Naveen

Re: [PATCH 3/3] powerpc64/ftrace: workaround clang recording GEP in __patchable_function_entries

[Naveen N Rao]

On Sun, Nov 09, 2025 at 02:34:05AM +0530, Hari Bathini wrote:
> Support for -fpatchable-function-entry on ppc64le was added in Clang
> with [1]. However, when no prefix NOPs are specified - as is the case
> with CONFIG_PPC_FTRACE_OUT_OF_LINE - the first NOP is emitted at LEP,
> but Clang records the Global Entry Point (GEP) unlike GCC which does
> record the Local Entry Point (LEP). Issue [2] has been raised to align
> Clang's behavior with GCC. As a temporary workaround to ensure ftrace

Any reason to put in a "temporary" workaround rather than waiting for 
this to be fixed?

- Naveen

Re: [PATCH 1/3] powerpc64: make clang cross-build friendly

[Hari Bathini]

Thanks for the review, Naveen.

On 24/11/25 11:19 am, Naveen N Rao wrote:
> On Sun, Nov 09, 2025 at 02:34:03AM +0530, Hari Bathini wrote:
>> ARCH_USING_PATCHABLE_FUNCTION_ENTRY depends on toolchain support for
>> -fpatchable-function-entry option. The current script that checks
>> for this support only handles GCC. Rename the script and extend it
>> to detect support for -fpatchable-function-entry with Clang as well,
>> allowing clean cross-compilation with Clang toolchains.
>>
>> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
>> ---
>>   arch/powerpc/Kconfig                                         | 5 +++--
>>   ...-function-entry.sh => check-fpatchable-function-entry.sh} | 0
>>   2 files changed, 3 insertions(+), 2 deletions(-)
>>   rename arch/powerpc/tools/{gcc-check-fpatchable-function-entry.sh => check-fpatchable-function-entry.sh} (100%)
>>
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index 325c1171894d..dfb62e211c92 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -568,8 +568,9 @@ config ARCH_USING_PATCHABLE_FUNCTION_ENTRY
>>   	depends on FUNCTION_TRACER && (PPC32 || PPC64_ELF_ABI_V2)
>>   	depends on $(cc-option,-fpatchable-function-entry=2)
>>   	def_bool y if PPC32
>> -	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
>> +	def_bool $(success,$(srctree)/arch/powerpc/tools/check-fpatchable-function-entry.sh $(CC) -mlittle-endian) if PPC64 && CPU_LITTLE_ENDIAN && CC_IS_GCC
>> +	def_bool $(success,$(srctree)/arch/powerpc/tools/check-fpatchable-function-entry.sh $(CC) -target ppc64le -mlittle-endian) if PPC64 && CPU_LITTLE_ENDIAN && CC_IS_CLANG
> 
> Can you instead pass $(CLANG_FLAGS) to retain the same command across
> gcc/clang?

Should work, I guess.
But do I need to test for any additional clang flags that
may interfere with what we are trying to check here?

- Hari

Re: [PATCH 3/3] powerpc64/ftrace: workaround clang recording GEP in __patchable_function_entries

[Hari Bathini]

On 24/11/25 11:25 am, Naveen N Rao wrote:
> On Sun, Nov 09, 2025 at 02:34:05AM +0530, Hari Bathini wrote:
>> Support for -fpatchable-function-entry on ppc64le was added in Clang
>> with [1]. However, when no prefix NOPs are specified - as is the case
>> with CONFIG_PPC_FTRACE_OUT_OF_LINE - the first NOP is emitted at LEP,
>> but Clang records the Global Entry Point (GEP) unlike GCC which does
>> record the Local Entry Point (LEP). Issue [2] has been raised to align
>> Clang's behavior with GCC. As a temporary workaround to ensure ftrace
> 
> Any reason to put in a "temporary" workaround rather than waiting for
> this to be fixed?

Pushing for this temporary workaround as the fix ETA for clang is not
available at the moment and the temporary workaround is likely
harmless even on a clang version with the fix included..

- Hari

Re: [PATCH 1/3] powerpc64: make clang cross-build friendly

[Naveen N Rao]

On Mon, Dec 08, 2025 at 09:32:06PM +0530, Hari Bathini wrote:
> Thanks for the review, Naveen.
> 
> On 24/11/25 11:19 am, Naveen N Rao wrote:
> > On Sun, Nov 09, 2025 at 02:34:03AM +0530, Hari Bathini wrote:
> > > ARCH_USING_PATCHABLE_FUNCTION_ENTRY depends on toolchain support for
> > > -fpatchable-function-entry option. The current script that checks
> > > for this support only handles GCC. Rename the script and extend it
> > > to detect support for -fpatchable-function-entry with Clang as well,
> > > allowing clean cross-compilation with Clang toolchains.
> > > 
> > > Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
> > > ---
> > >   arch/powerpc/Kconfig                                         | 5 +++--
> > >   ...-function-entry.sh => check-fpatchable-function-entry.sh} | 0
> > >   2 files changed, 3 insertions(+), 2 deletions(-)
> > >   rename arch/powerpc/tools/{gcc-check-fpatchable-function-entry.sh => check-fpatchable-function-entry.sh} (100%)
> > > 
> > > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > > index 325c1171894d..dfb62e211c92 100644
> > > --- a/arch/powerpc/Kconfig
> > > +++ b/arch/powerpc/Kconfig
> > > @@ -568,8 +568,9 @@ config ARCH_USING_PATCHABLE_FUNCTION_ENTRY
> > >   	depends on FUNCTION_TRACER && (PPC32 || PPC64_ELF_ABI_V2)
> > >   	depends on $(cc-option,-fpatchable-function-entry=2)
> > >   	def_bool y if PPC32
> > > -	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
> > > +	def_bool $(success,$(srctree)/arch/powerpc/tools/check-fpatchable-function-entry.sh $(CC) -mlittle-endian) if PPC64 && CPU_LITTLE_ENDIAN && CC_IS_GCC
> > > +	def_bool $(success,$(srctree)/arch/powerpc/tools/check-fpatchable-function-entry.sh $(CC) -target ppc64le -mlittle-endian) if PPC64 && CPU_LITTLE_ENDIAN && CC_IS_CLANG
> > 
> > Can you instead pass $(CLANG_FLAGS) to retain the same command across
> > gcc/clang?
> 
> Should work, I guess.
> But do I need to test for any additional clang flags that
> may interfere with what we are trying to check here?

From what I can tell, $(CLANG_FLAGS) includes a fairly static set of 
flags which will be included alongside other $CFLAGS. So, I don't think 
anything special should be needed there.

- Naveen