[PATCH RFC v2 0/5] kernel-hacking: introduce CONFIG_NO_AUTO_INLINE

[PATCH RFC v2 0/5] kernel-hacking: introduce CONFIG_NO_AUTO_INLINE

[Chen Linxuan via B4 Relay]

This series introduces a new kernel configuration option NO_AUTO_INLINE,
which can be used to disable the automatic inlining of functions.

This will allow the function tracer to trace more functions
because it only traces functions that the compiler has not inlined.

Previous discussions can be found at

Link: https://lore.kernel.org/all/20181028130945.23581-3-changbin.du@gmail.com/

And v1 of this series can be found at

Link: https://lore.kernel.org/all/31F42D8141CDD2D0+20250411105142.89296-1-chenlinxuan@uniontech.com/

This patch depends on

  [PATCH] drm/i915/pxp: fix undefined reference to
          `intel_pxp_gsccs_is_ready_for_sessions'

which can be found at

  https://lore.kernel.org/all/20250415090616.2649889-1-jani.nikula@intel.com/

as well as

  [RFC PATCH 5/7] RDMA/hns: initialize db in update_srq_db()

which can be found at

  https://lore.kernel.org/all/FF922C77946229B6+20250411105459.90782-5-chenlinxuan@uniontech.com/

Signed-off-by: Chen Linxuan <chenlinxuan@uniontech.com>
---
Winston Wen (5):
      nvme: add __always_inline for nvme_pci_npages_prp
      mm: add __always_inline for page_contains_unaccepted
      vfio/virtio: add __always_inline for virtiovf_get_device_config_size
      tpm: add __always_inline for tpm_is_hwrng_enabled
      lib/Kconfig.debug: introduce CONFIG_NO_AUTO_INLINE

 Makefile                            |  6 ++++++
 drivers/char/tpm/tpm-chip.c         |  2 +-
 drivers/nvme/host/pci.c             |  2 +-
 drivers/vfio/pci/virtio/legacy_io.c |  2 +-
 lib/Kconfig.debug                   | 15 +++++++++++++++
 mm/page_alloc.c                     |  2 +-
 6 files changed, 25 insertions(+), 4 deletions(-)
---
base-commit: 1a1d569a75f3ab2923cb62daf356d102e4df2b86
change-id: 20250416-noautoinline-8e9b9e535452

Best regards,
-- 
Chen Linxuan <chenlinxuan@uniontech.com>

[PATCH RFC v2 1/5] nvme: add __always_inline for nvme_pci_npages_prp

[Chen Linxuan via B4 Relay]

From: Winston Wen <wentao@uniontech.com>

On x86_64 with gcc version 13.3.0, I build drivers/nvme/host/pci.c
with:

  make defconfig
  ./scripts/kconfig/merge_config.sh .config <(
    echo CONFIG_BLK_DEV_NVME=m
  )
  make KCFLAGS="-fno-inline-small-functions -fno-inline-functions-called-once" \
    drivers/nvme/host/pci.o

Then I get a compile error:

    CALL    scripts/checksyscalls.sh
    DESCEND objtool
    INSTALL libsubcmd_headers
    CC      drivers/nvme/host/pci.o
  In file included from <command-line>:
  drivers/nvme/host/pci.c: In function 'nvme_init':
  ././include/linux/compiler_types.h:557:45: error: call to '__compiletime_assert_878' declared with attribute error: BUILD_BUG_ON failed: nvme_pci_npages_prp() > NVME_MAX_NR_ALLOCATIONS
    557 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
        |                                             ^
  ././include/linux/compiler_types.h:538:25: note: in definition of macro '__compiletime_assert'
    538 |                         prefix ## suffix();                             \
        |                         ^~~~~~
  ././include/linux/compiler_types.h:557:9: note: in expansion of macro '_compiletime_assert'
    557 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
        |         ^~~~~~~~~~~~~~~~~~~
  ./include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
     39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
        |                                     ^~~~~~~~~~~~~~~~~~
  ./include/linux/build_bug.h:50:9: note: in expansion of macro 'BUILD_BUG_ON_MSG'
     50 |         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
        |         ^~~~~~~~~~~~~~~~
  drivers/nvme/host/pci.c:3804:9: note: in expansion of macro 'BUILD_BUG_ON'
   3804 |         BUILD_BUG_ON(nvme_pci_npages_prp() > NVME_MAX_NR_ALLOCATIONS);
        |         ^~~~~~~~~~~~

Mark nvme_pci_npages_prp() with __always_inline make it can be computed
at compile time.

Co-developed-by: Chen Linxuan <chenlinxuan@uniontech.com>
Signed-off-by: Chen Linxuan <chenlinxuan@uniontech.com>
Signed-off-by: Winston Wen <wentao@uniontech.com>
---
 drivers/nvme/host/pci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index b178d52eac1b7f7286e217226b9b3686d07b7b6c..9ab070a9f0372bc6595c29a884ee9f2ffe5ae8e9 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -390,7 +390,7 @@ static bool nvme_dbbuf_update_and_check_event(u16 value, __le32 *dbbuf_db,
  * as it only leads to a small amount of wasted memory for the lifetime of
  * the I/O.
  */
-static int nvme_pci_npages_prp(void)
+static __always_inline int nvme_pci_npages_prp(void)
 {
 	unsigned max_bytes = (NVME_MAX_KB_SZ * 1024) + NVME_CTRL_PAGE_SIZE;
 	unsigned nprps = DIV_ROUND_UP(max_bytes, NVME_CTRL_PAGE_SIZE);

-- 
2.48.1

[PATCH RFC v2 2/5] mm: add __always_inline for page_contains_unaccepted

[Chen Linxuan via B4 Relay]

From: Winston Wen <wentao@uniontech.com>

On x86_64 with gcc version 13.3.0, I compile mm/page_alloc.c with:

  make defconfig
  make KCFLAGS="-fno-inline-small-functions -fno-inline-functions-called-once" \
    mm/page_alloc.o

Then I get a compile error:

    CALL    scripts/checksyscalls.sh
    DESCEND objtool
    INSTALL libsubcmd_headers
    CC      mm/page_alloc.o
  In file included from <command-line>:
  mm/page_alloc.c: In function '__free_unaccepted.isra':
  ././include/linux/compiler_types.h:557:45: error: call to '__compiletime_assert_1013' declared with attribute error: BUILD_BUG failed
    557 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
        |                                             ^
  ././include/linux/compiler_types.h:538:25: note: in definition of macro '__compiletime_assert'
    538 |                         prefix ## suffix();                             \
        |                         ^~~~~~
  ././include/linux/compiler_types.h:557:9: note: in expansion of macro '_compiletime_assert'
    557 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
        |         ^~~~~~~~~~~~~~~~~~~
  ./include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
     39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
        |                                     ^~~~~~~~~~~~~~~~~~
  ./include/linux/build_bug.h:59:21: note: in expansion of macro 'BUILD_BUG_ON_MSG'
     59 | #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
        |                     ^~~~~~~~~~~~~~~~
  mm/page_alloc.c:7301:9: note: in expansion of macro 'BUILD_BUG'
   7301 |         BUILD_BUG();
        |         ^~~~~~~~~

Marking page_contains_unaccepted with __always_inline and let dead code
elimination remove reference to __free_unaccepted() here.

Co-developed-by: Chen Linxuan <chenlinxuan@uniontech.com>
Signed-off-by: Chen Linxuan <chenlinxuan@uniontech.com>
Signed-off-by: Winston Wen <wentao@uniontech.com>
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fd6b865cb1abfbd3d2ebd67cdaa5f86d92a62e14..7c0934c818ddc719c2dcb813599708f47d56352c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7286,7 +7286,7 @@ static bool __free_unaccepted(struct page *page)
 
 #else
 
-static bool page_contains_unaccepted(struct page *page, unsigned int order)
+static __always_inline bool page_contains_unaccepted(struct page *page, unsigned int order)
 {
 	return false;
 }

-- 
2.48.1

[PATCH RFC v2 3/5] vfio/virtio: add __always_inline for virtiovf_get_device_config_size

[Chen Linxuan via B4 Relay]

From: Winston Wen <wentao@uniontech.com>

Presume that kernel is compiled for x86_64 with gcc version 13.3.0:

  make defconfig
  ./scripts/kconfig/merge_config.sh .config <(
    echo CONFIG_VFIO=m
    echo CONFIG_VIRTIO_PCI=y
    echo CONFIG_VIRTIO_PCI_LIB_LEGACY=y
    echo CONFIG_VIRTIO_VFIO_PCI=m
    echo CONFIG_VIRTIO_VFIO_PCI_ADMIN_LEGACY=y
  )
  make KCFLAGS="-fno-inline-small-functions -fno-inline-functions-called-once" \
    drivers/vfio/pci/virtio/legacy_io.o

This results a compile error:

    CALL    scripts/checksyscalls.sh
    DESCEND objtool
    INSTALL libsubcmd_headers
    CC      drivers/vfio/pci/virtio/legacy_io.o
  In file included from <command-line>:
  drivers/vfio/pci/virtio/legacy_io.c: In function 'virtiovf_init_legacy_io':
  ././include/linux/compiler_types.h:557:45: error: call to '__compiletime_assert_889' declared with attribute error: BUILD_BUG_ON failed: !is_power_of_2(virtvdev->bar0_virtual_buf_size)
    557 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
        |                                             ^
  ././include/linux/compiler_types.h:538:25: note: in definition of macro '__compiletime_assert'
    538 |                         prefix ## suffix();                             \
        |                         ^~~~~~
  ././include/linux/compiler_types.h:557:9: note: in expansion of macro '_compiletime_assert'
    557 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
        |         ^~~~~~~~~~~~~~~~~~~
  ./include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
     39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
        |                                     ^~~~~~~~~~~~~~~~~~
  ./include/linux/build_bug.h:50:9: note: in expansion of macro 'BUILD_BUG_ON_MSG'
     50 |         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
        |         ^~~~~~~~~~~~~~~~
  drivers/vfio/pci/virtio/legacy_io.c:401:9: note: in expansion of macro 'BUILD_BUG_ON'
    401 |         BUILD_BUG_ON(!is_power_of_2(virtvdev->bar0_virtual_buf_size));
        |         ^~~~~~~~~~~~

BUILD_BUG_ON needs virtvdev->bar0_virtual_buf_size to be computed at
compile time. So we should mark virtiovf_get_device_config_size() with
__always_inline here.

Co-developed-by: Chen Linxuan <chenlinxuan@uniontech.com>
Signed-off-by: Chen Linxuan <chenlinxuan@uniontech.com>
Signed-off-by: Winston Wen <wentao@uniontech.com>
---
 drivers/vfio/pci/virtio/legacy_io.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/virtio/legacy_io.c b/drivers/vfio/pci/virtio/legacy_io.c
index 832af5ba267c49a079009cfe0fa93c15ba7a490f..b6871d50b9f9e278ef3c49a9cb2baf474b8271c6 100644
--- a/drivers/vfio/pci/virtio/legacy_io.c
+++ b/drivers/vfio/pci/virtio/legacy_io.c
@@ -350,7 +350,7 @@ int virtiovf_open_legacy_io(struct virtiovf_pci_core_device *virtvdev)
 	return virtiovf_set_notify_addr(virtvdev);
 }
 
-static int virtiovf_get_device_config_size(unsigned short device)
+static __always_inline int virtiovf_get_device_config_size(unsigned short device)
 {
 	/* Network card */
 	return offsetofend(struct virtio_net_config, status);

-- 
2.48.1

[PATCH RFC v2 4/5] tpm: add __always_inline for tpm_is_hwrng_enabled

[Chen Linxuan via B4 Relay]

From: Winston Wen <wentao@uniontech.com>

Presume that kernel is compiled for x86_64 with gcc version 13.3.0:

  make defconfig
  ./scripts/kconfig/merge_config.sh .config <(
    echo CONFIG_TCG_TPM=y
    echo CONFIG_HW_RANDOM=m
  )
  make KCFLAGS="-fno-inline-small-functions -fno-inline-functions-called-once"

This results a link error:

  ld: vmlinux.o: in function `tpm_add_hwrng':
  tpm-chip.c:(.text+0x6c5924): undefined reference to `hwrng_register'
  ld: vmlinux.o: in function `tpm_chip_unregister':
  (.text+0x6c5bc9): undefined reference to `hwrng_unregister'
  ld: vmlinux.o: in function `tpm_chip_register':
  (.text+0x6c5c9b): undefined reference to `hwrng_unregister'

With `CONFIG_TCG_TPM=y` and `CONFIG_HW_RANDOM=m`,
the functions `tpm_add_hwrng`, `tpm_chip_unregister`, and
`tpm_chip_register` are compiled into `vmlinux.o`
and reference the symbols `hwrng_register` and `hwrng_unregister`.
These symbols, however, are compiled into `rng-core.ko`, which results
in the linking error.

I am not sure but I think this weird linking error only arises when
auto inlining is disabled because of some dead code elimination.

`CONFIG_TCG_TPM=y` and `CONFIG_HW_RANDOM=m` set `CONFIG_HW_RANDOM_TPM=n`.
This causes the function `tpm_is_hwrng_enabled` to always return
`false`, as shown below:

  static bool tpm_is_hwrng_enabled(struct tpm_chip *chip)
  {
      if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM))
          return false;
      if (tpm_is_firmware_upgrade(chip))
          return false;
      if (chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED)
          return false;
      return true;
  }

When `tpm_is_hwrng_enabled` is inlined, dead code elimination
optimizations are applied and the reference to the `hwrng_*` functions
will been removed.
For instance, in the `tpm_chip_unregister` function:

  void tpm_chip_unregister(struct tpm_chip *chip)
  {
  #ifdef CONFIG_TCG_TPM2_HMAC
      int rc;

      rc = tpm_try_get_ops(chip);
      if (!rc) {
          tpm2_end_auth_session(chip);
          tpm_put_ops(chip);
      }
  #endif

      tpm_del_legacy_sysfs(chip);
      if (tpm_is_hwrng_enabled(chip))
          hwrng_unregister(&chip->hwrng);
      tpm_bios_log_teardown(chip);
      if (chip->flags & TPM_CHIP_FLAG_TPM2 && !tpm_is_firmware_upgrade(chip))
          tpm_devs_remove(chip);
      tpm_del_char_device(chip);
  }

When `tpm_is_hwrng_enabled` is inlined and always returns `false`,
the call to `hwrng_unregister` is effectively part of a `if (false)`
block, which I guess that will be then optimized out.

However, when the `-fno-inline-small-functions` and
`-fno-inline-functions-called-once` flags are used,
tpm_is_hwrng_enabled is not inline.

And this optimization some how cannot occur,
leading to the undefined reference errors during linking.

Adding the `__always_inline` attribute ensures that
`tpm_is_hwrng_enabled` is inlined regardless of the compiler flags.
This allows the dead code elimination to proceed as expected,
resolving the linking issue.

Co-developed-by: Chen Linxuan <chenlinxuan@uniontech.com>
Signed-off-by: Chen Linxuan <chenlinxuan@uniontech.com>
Signed-off-by: Winston Wen <wentao@uniontech.com>
---
 drivers/char/tpm/tpm-chip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index e25daf2396d37bcaeae8a96267764df0861ad1be..48cc74d84247e258a39f2118e03aa10d0cbb066a 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -534,7 +534,7 @@ static int tpm_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 	return tpm_get_random(chip, data, max);
 }
 
-static bool tpm_is_hwrng_enabled(struct tpm_chip *chip)
+static __always_inline bool tpm_is_hwrng_enabled(struct tpm_chip *chip)
 {
 	if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM))
 		return false;

-- 
2.48.1

Re: [PATCH RFC v2 4/5] tpm: add __always_inline for tpm_is_hwrng_enabled

[Jarkko Sakkinen]

On Wed, Apr 16, 2025 at 05:44:50PM +0800, Chen Linxuan via B4 Relay wrote:
> From: Winston Wen <wentao@uniontech.com>
> 
> Presume that kernel is compiled for x86_64 with gcc version 13.3.0:
> 
>   make defconfig
>   ./scripts/kconfig/merge_config.sh .config <(
>     echo CONFIG_TCG_TPM=y
>     echo CONFIG_HW_RANDOM=m
>   )
>   make KCFLAGS="-fno-inline-small-functions -fno-inline-functions-called-once"
> 
> This results a link error:
> 
>   ld: vmlinux.o: in function `tpm_add_hwrng':
>   tpm-chip.c:(.text+0x6c5924): undefined reference to `hwrng_register'
>   ld: vmlinux.o: in function `tpm_chip_unregister':
>   (.text+0x6c5bc9): undefined reference to `hwrng_unregister'
>   ld: vmlinux.o: in function `tpm_chip_register':
>   (.text+0x6c5c9b): undefined reference to `hwrng_unregister'
> 
> With `CONFIG_TCG_TPM=y` and `CONFIG_HW_RANDOM=m`,
> the functions `tpm_add_hwrng`, `tpm_chip_unregister`, and
> `tpm_chip_register` are compiled into `vmlinux.o`
> and reference the symbols `hwrng_register` and `hwrng_unregister`.
> These symbols, however, are compiled into `rng-core.ko`, which results
> in the linking error.
> 
> I am not sure but I think this weird linking error only arises when
> auto inlining is disabled because of some dead code elimination.
> 
> `CONFIG_TCG_TPM=y` and `CONFIG_HW_RANDOM=m` set `CONFIG_HW_RANDOM_TPM=n`.
> This causes the function `tpm_is_hwrng_enabled` to always return
> `false`, as shown below:
> 
>   static bool tpm_is_hwrng_enabled(struct tpm_chip *chip)
>   {
>       if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM))
>           return false;
>       if (tpm_is_firmware_upgrade(chip))
>           return false;
>       if (chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED)
>           return false;
>       return true;
>   }
> 
> When `tpm_is_hwrng_enabled` is inlined, dead code elimination
> optimizations are applied and the reference to the `hwrng_*` functions
> will been removed.
> For instance, in the `tpm_chip_unregister` function:
> 
>   void tpm_chip_unregister(struct tpm_chip *chip)
>   {
>   #ifdef CONFIG_TCG_TPM2_HMAC
>       int rc;
> 
>       rc = tpm_try_get_ops(chip);
>       if (!rc) {
>           tpm2_end_auth_session(chip);
>           tpm_put_ops(chip);
>       }
>   #endif
> 
>       tpm_del_legacy_sysfs(chip);
>       if (tpm_is_hwrng_enabled(chip))
>           hwrng_unregister(&chip->hwrng);
>       tpm_bios_log_teardown(chip);
>       if (chip->flags & TPM_CHIP_FLAG_TPM2 && !tpm_is_firmware_upgrade(chip))
>           tpm_devs_remove(chip);
>       tpm_del_char_device(chip);
>   }
> 
> When `tpm_is_hwrng_enabled` is inlined and always returns `false`,
> the call to `hwrng_unregister` is effectively part of a `if (false)`
> block, which I guess that will be then optimized out.
> 
> However, when the `-fno-inline-small-functions` and
> `-fno-inline-functions-called-once` flags are used,
> tpm_is_hwrng_enabled is not inline.
> 
> And this optimization some how cannot occur,
> leading to the undefined reference errors during linking.
> 
> Adding the `__always_inline` attribute ensures that
> `tpm_is_hwrng_enabled` is inlined regardless of the compiler flags.
> This allows the dead code elimination to proceed as expected,
> resolving the linking issue.
> 
> Co-developed-by: Chen Linxuan <chenlinxuan@uniontech.com>
> Signed-off-by: Chen Linxuan <chenlinxuan@uniontech.com>
> Signed-off-by: Winston Wen <wentao@uniontech.com>
> ---
>  drivers/char/tpm/tpm-chip.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index e25daf2396d37bcaeae8a96267764df0861ad1be..48cc74d84247e258a39f2118e03aa10d0cbb066a 100644
> --- a/drivers/char/tpm/tpm-chip.c
> +++ b/drivers/char/tpm/tpm-chip.c
> @@ -534,7 +534,7 @@ static int tpm_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
>  	return tpm_get_random(chip, data, max);
>  }
>  
> -static bool tpm_is_hwrng_enabled(struct tpm_chip *chip)
> +static __always_inline bool tpm_is_hwrng_enabled(struct tpm_chip *chip)
>  {
>  	if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM))
>  		return false;
> 
> -- 
> 2.48.1
> 
> 
> 

Thank you.

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>


BR, Jarkko

[PATCH RFC v2 5/5] lib/Kconfig.debug: introduce CONFIG_NO_AUTO_INLINE

[Chen Linxuan via B4 Relay]

From: Winston Wen <wentao@uniontech.com>

Add a new kernel hacking option CONFIG_NO_AUTO_INLINE that prevents the
compiler from auto-inlining functions not explicitly marked with the
'inline' keyword.

This enhancement improves function tracer capabilities as it can only
trace functions that haven't been inlined by the compiler.

Previous discussions:

Link: https://lore.kernel.org/all/20181028130945.23581-3-changbin.du@gmail.com/

This patch is modified from commit 917fad29febd ("kernel hacking: add a
config option to disable compiler auto-inlining") which can be founded
in linux-next-history:

Link: https://web.git.kernel.org/pub/scm/linux/kernel/git/next/linux-next-history.git/commit/?id=917fad29febd

Unlike the original implementation, this patch:

1. Make it depends on CC_IS_GCC,
   as Clang 18.1.3 break test_bitmap_const_eval() in lib/test_bitmap.c

2. Make it depends on X86 and LOONGARCH,
   as I haven't test other architectures

3. Removes unnecessary cc-option checks per commit 7d73c3e9c514
   ("Makefile: remove stale cc-option checks").

4. Update help information.

Cc: Changbin Du <changbin.du@gmail.com>
Co-developed-by: Chen Linxuan <chenlinxuan@uniontech.com>
Signed-off-by: Chen Linxuan <chenlinxuan@uniontech.com>
Signed-off-by: Winston Wen <wentao@uniontech.com>
---
 Makefile          |  6 ++++++
 lib/Kconfig.debug | 15 +++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/Makefile b/Makefile
index c91afd55099ea6bc7ed89bc3ef9cf58a498596d4..52da2c27f94167d2d2892a67c065e5df15efbde0 100644
--- a/Makefile
+++ b/Makefile
@@ -1071,6 +1071,12 @@ endif
 # Ensure compilers do not transform certain loops into calls to wcslen()
 KBUILD_CFLAGS += -fno-builtin-wcslen
 
+ifdef CONFIG_NO_AUTO_INLINE
+KBUILD_CFLAGS   += -fno-inline-functions \
+		   -fno-inline-small-functions \
+		   -fno-inline-functions-called-once
+endif
+
 # change __FILE__ to the relative path to the source directory
 ifdef building_out_of_srctree
 KBUILD_CPPFLAGS += $(call cc-option,-ffile-prefix-map=$(srcroot)/=)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 9fe4d8dfe5782981cc0b2b6614106aac570bd229..2ebb4802886ab4a48841dbdd8973b7d9883548b9 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -436,8 +436,23 @@ config GDB_SCRIPTS
 	  instance. See Documentation/process/debugging/gdb-kernel-debugging.rst
 	  for further details.
 
+
 endif # DEBUG_INFO
 
+config NO_AUTO_INLINE
+	bool "Disable compiler auto-inline optimizations (EXPERIMENTAL)"
+	default n
+	depends on CC_IS_GCC && (X86 || LOONGARCH)
+	help
+	  This will prevent the compiler from optimizing the kernel by
+	  auto-inlining functions not marked with the inline keyword.
+	  With this option, only functions explicitly marked with
+	  "inline" will be inlined. This will allow the function tracer
+	  to trace more functions because it only traces functions that
+	  the compiler has not inlined.
+
+	  If unsure, select N.
+
 config FRAME_WARN
 	int "Warn for stack frames larger than"
 	range 0 8192

-- 
2.48.1

Re: [PATCH RFC v2 5/5] lib/Kconfig.debug: introduce CONFIG_NO_AUTO_INLINE

[Bart Van Assche]

On 4/16/25 2:44 AM, Chen Linxuan via B4 Relay wrote:
> 2. Make it depends on X86 and LOONGARCH,
>     as I haven't test other architectures

That sounds weird to me. Shouldn't this option be made architecture-
independent?

> +config NO_AUTO_INLINE
> +	bool "Disable compiler auto-inline optimizations (EXPERIMENTAL)"
> +	default n
> +	depends on CC_IS_GCC && (X86 || LOONGARCH)

Why "depends on CC_IS_GCC"? Please make sure that both gcc and clang are
supported.

Thanks,

Bart.

Re: [PATCH RFC v2 5/5] lib/Kconfig.debug: introduce CONFIG_NO_AUTO_INLINE

[Chen Linxuan]

On 4/17/25 5:04 PM, Bart Van Assche wrote:
> On 4/16/25 2:44 AM, Chen Linxuan via B4 Relay wrote:
> > 2. Make it depends on X86 and LOONGARCH,
> >     as I haven't test other architectures
> 
> That sounds weird to me. Shouldn't this option be made architecture-
> independent?

It should, but I have only tested it on X86 and LOONGARCH.

> 
> > +config NO_AUTO_INLINE
> > +	bool "Disable compiler auto-inline optimizations (EXPERIMENTAL)"
> > +	default n
> > +	depends on CC_IS_GCC && (X86 || LOONGARCH)
> 
> Why "depends on CC_IS_GCC"? Please make sure that both gcc and clang are
> supported.

I make it depends on CC_IS_GCC because

1. Clang do not have `-fno-inline-small-functions`
   and `-fno-inline-functions-called-once`.

2. If we wrap those options with cc-option,
   Clang 18.1.3 fails to compile test_bitmap_const_eval(),
   with config KASAN and TEST_BITMAP is enabled.

   Comments above test_bitmap_const_eval() says that:

   > /*
   >  * FIXME: Clang breaks compile-time evaluations when KASAN and GCOV are enabled.
   >  * To workaround it, GCOV is force-disabled in Makefile for this configuration.
   >  */

   It seems there are some issues with Clang's compile-time evaluations.

So I think there are some ways to workaround this problem:

1. Make NO_AUTO_INLINE depends on CC_IS_GCC;
2. Make NO_AUTO_INLINE depends on KASAN=n;
3. Disable NO_AUTO_INLINE for TEST_BITMAP
   like how we handle CC_IS_CLANG && KASAN && GCOV in lib/Makefile:

   > ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_KASAN),yy)
   > # FIXME: Clang breaks test_bitmap_const_eval when KASAN and GCOV are enabled
   > GCOV_PROFILE_test_bitmap.o := n
   > endif

Which one do you prefer or do you have any other suggestions?

> 
> Thanks,
> 
> Bart.