CONFIG_LD_DEAD_CODE_DATA_ELIMINATION: Section mismatch in reference from the variable via_pmu_driver to the function .init.text:pmu_init()

4 messages, 3 authors, 2018-07-03 · open the first message on its own page

CONFIG_LD_DEAD_CODE_DATA_ELIMINATION: Section mismatch in reference from the variable via_pmu_driver to the function .init.text:pmu_init()

From: Mathieu Malaterre <hidden>
Date: 2018-07-03 09:40:21

Hi Nick,

Would you consider this a bug:

$ touch drivers/macintosh/via-pmu.c
$ CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=n make ARCH=powerpc
CROSS_COMPILE=powerpc-linux-gnu-
...
  LD      vmlinux.o
  MODPOST vmlinux.o
WARNING: vmlinux.o(.data+0x216018): Section mismatch in reference from
the variable via_pmu_driver to the function .init.text:pmu_init()
The variable via_pmu_driver references
the function __init pmu_init()
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

While:

$ touch drivers/macintosh/via-pmu.c
$ CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y make ARCH=powerpc
CROSS_COMPILE=powerpc-linux-gnu-
...
  AR      init/built-in.a
  AR      built-in.a
  LD      vmlinux.o
  MODPOST vmlinux.o
  KSYM    .tmp_kallsyms1.o
  KSYM    .tmp_kallsyms2.o
  LD      vmlinux
  SORTEX  vmlinux
  SYSMAP  System.map
...

Thanks for comment

Re: CONFIG_LD_DEAD_CODE_DATA_ELIMINATION: Section mismatch in reference from the variable via_pmu_driver to the function .init.text:pmu_init()

From: Christophe LEROY <hidden>
Date: 2018-07-03 10:07:12


Le 03/07/2018 à 11:40, Mathieu Malaterre a écrit :

Hi Nick,

Would you consider this a bug:

Looks more like a feature ...

In /drivers/macintosh/adb.c you have, and it's the only place 
via_pmu_driver is used.

#if defined(CONFIG_ADB_PMU) || defined(CONFIG_ADB_PMU68K)
	&via_pmu_driver,
#endif

Is one of those defined in your .config ? If not then via_pmu_driver 
gets eliminated hence nothing to warn on.


Christophe

$ touch drivers/macintosh/via-pmu.c
$ CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=n make ARCH=powerpc
CROSS_COMPILE=powerpc-linux-gnu-
...
   LD      vmlinux.o
   MODPOST vmlinux.o
WARNING: vmlinux.o(.data+0x216018): Section mismatch in reference from
the variable via_pmu_driver to the function .init.text:pmu_init()
The variable via_pmu_driver references
the function __init pmu_init()
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

While:

$ touch drivers/macintosh/via-pmu.c
$ CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y make ARCH=powerpc
CROSS_COMPILE=powerpc-linux-gnu-
...
   AR      init/built-in.a
   AR      built-in.a
   LD      vmlinux.o
   MODPOST vmlinux.o
   KSYM    .tmp_kallsyms1.o
   KSYM    .tmp_kallsyms2.o
   LD      vmlinux
   SORTEX  vmlinux
   SYSMAP  System.map
...

Thanks for comment

Re: CONFIG_LD_DEAD_CODE_DATA_ELIMINATION: Section mismatch in reference from the variable via_pmu_driver to the function .init.text:pmu_init()

From: Mathieu Malaterre <hidden>
Date: 2018-07-03 11:41:10

On Tue, Jul 3, 2018 at 11:40 AM Mathieu Malaterre [off-list ref] wrote:

Hi Nick,

Would you consider this a bug:

$ touch drivers/macintosh/via-pmu.c
$ CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=n make ARCH=powerpc
CROSS_COMPILE=powerpc-linux-gnu-
...
  LD      vmlinux.o
  MODPOST vmlinux.o
WARNING: vmlinux.o(.data+0x216018): Section mismatch in reference from
the variable via_pmu_driver to the function .init.text:pmu_init()
The variable via_pmu_driver references
the function __init pmu_init()
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

While:

$ touch drivers/macintosh/via-pmu.c
$ CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y make ARCH=powerpc
CROSS_COMPILE=powerpc-linux-gnu-
...
  AR      init/built-in.a
  AR      built-in.a
  LD      vmlinux.o
  MODPOST vmlinux.o
  KSYM    .tmp_kallsyms1.o
  KSYM    .tmp_kallsyms2.o
  LD      vmlinux
  SORTEX  vmlinux
  SYSMAP  System.map
...

Thanks for comment

Just to clarify I reverted 58935176ad17976b7a7f6ea25c0ceb2ca4308a30
just as to reproduce a warning. So my question (rephrased):

Is this expected that CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y inhibit
the behavior of  CONFIG_DEBUG_SECTION_MISMATCH=y ?

Thanks

Re: CONFIG_LD_DEAD_CODE_DATA_ELIMINATION: Section mismatch in reference from the variable via_pmu_driver to the function .init.text:pmu_init()

From: Nicholas Piggin <npiggin@gmail.com>
Date: 2018-07-03 12:15:54

On Tue, 3 Jul 2018 13:40:55 +0200
Mathieu Malaterre [off-list ref] wrote:

On Tue, Jul 3, 2018 at 11:40 AM Mathieu Malaterre [off-list ref] wrote:

quoted

Hi Nick,

Would you consider this a bug:

$ touch drivers/macintosh/via-pmu.c
$ CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=n make ARCH=powerpc
CROSS_COMPILE=powerpc-linux-gnu-
...
  LD      vmlinux.o
  MODPOST vmlinux.o
WARNING: vmlinux.o(.data+0x216018): Section mismatch in reference from
the variable via_pmu_driver to the function .init.text:pmu_init()
The variable via_pmu_driver references
the function __init pmu_init()
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

While:

$ touch drivers/macintosh/via-pmu.c
$ CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y make ARCH=powerpc
CROSS_COMPILE=powerpc-linux-gnu-
...
  AR      init/built-in.a
  AR      built-in.a
  LD      vmlinux.o
  MODPOST vmlinux.o
  KSYM    .tmp_kallsyms1.o
  KSYM    .tmp_kallsyms2.o
  LD      vmlinux
  SORTEX  vmlinux
  SYSMAP  System.map
...

Thanks for comment

Just to clarify I reverted 58935176ad17976b7a7f6ea25c0ceb2ca4308a30
just as to reproduce a warning. So my question (rephrased):

Is this expected that CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y inhibit
the behavior of  CONFIG_DEBUG_SECTION_MISMATCH=y ?

Well that's a good question actually. Section mismatch
analysis is done on the throwaway vmlinux.o which is not linked
with --gc-sections (and is not a final link), so the via_pmu_driver
symbol should exist and be picked up.

I wonder if something about the  -ffunction-sections is breaking
the reference detection.

Thanks,
Nick

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