spl/thread: explicitly define thread_func_t as noreturn
#16673
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All of our thread entry functions have this signature:
void (*)(void*) __attribute__((noreturn))
The low-level `__thread_create()` function accepts a `thread_func_t` as
the entry point, which is defined more simply as:
void (*)(void *)
And then the `thread_create()` and `thread_create_named()` macros cast
the passed-in function point down to `thread_func_t`, that is, casting
away the `noreturn` attribute.
Clang considers casting between these two types to be invalid because
both the caller and the callee may have elided parts of the stack frame
save and restore, knowing that they won't be needed.
Recent Linux appears to be setting `-Wcast-function-type-strict`, which
causes this invalid cast to emit a warning, which with `-Werror` is
converted to an error, breaking the build.
This commit fixes this in the simplest possible way: adding `noreturn`
to the `thread_func_t` attribute. Since all our thread entry functions
already have this attribute, it's arguably a just a consistency fix
anyway.
I considered removing the casts in the macros, which silences the
warnings, but it turns out that Clang has a bug that won't emit this
error for implicit conversions, only explicit casts. So leaving them
there seems like a reasonable belt-and-suspenders approach. Also,
frankly, this whole mechanism seems a little undercooked inside LLVM, so
I'm content go with my intuition about the smallest, least invaisve
change.
**NOTE**: `__thread_create` is exported by `spl.ko` and has a
`thread_func_t` arg, so this is an ABI break. Whether that matters in
practice, I have no idea.
Further reading:
- llvm/llvm-project@1aad641
- llvm/llvm-project#7325
- llvm/llvm-project#41465
Sponsored-by: https://despairlabs.com/sponsor/
Signed-off-by: Rob Norris <robn@despairlabs.com>
behlendorf
approved these changes
Oct 21, 2024
behlendorf
pushed a commit
to behlendorf/zfs
that referenced
this pull request
Oct 21, 2024
All of our thread entry functions have this signature:
void (*)(void*) __attribute__((noreturn))
The low-level `__thread_create()` function accepts a `thread_func_t` as
the entry point, which is defined more simply as:
void (*)(void *)
And then the `thread_create()` and `thread_create_named()` macros cast
the passed-in function point down to `thread_func_t`, that is, casting
away the `noreturn` attribute.
Clang considers casting between these two types to be invalid because
both the caller and the callee may have elided parts of the stack frame
save and restore, knowing that they won't be needed.
Recent Linux appears to be setting `-Wcast-function-type-strict`, which
causes this invalid cast to emit a warning, which with `-Werror` is
converted to an error, breaking the build.
This commit fixes this in the simplest possible way: adding `noreturn`
to the `thread_func_t` attribute. Since all our thread entry functions
already have this attribute, it's arguably a just a consistency fix
anyway.
I considered removing the casts in the macros, which silences the
warnings, but it turns out that Clang has a bug that won't emit this
error for implicit conversions, only explicit casts. So leaving them
there seems like a reasonable belt-and-suspenders approach. Also,
frankly, this whole mechanism seems a little undercooked inside LLVM, so
I'm content go with my intuition about the smallest, least invaisve
change.
**NOTE**: `__thread_create` is exported by `spl.ko` and has a
`thread_func_t` arg, so this is an ABI break. Whether that matters in
practice, I have no idea.
Further reading:
- llvm/llvm-project@1aad641
- llvm/llvm-project#7325
- llvm/llvm-project#41465
Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes openzfs#16672
Closes openzfs#16673
behlendorf
pushed a commit
to behlendorf/zfs
that referenced
this pull request
Oct 21, 2024
All of our thread entry functions have this signature:
void (*)(void*) __attribute__((noreturn))
The low-level `__thread_create()` function accepts a `thread_func_t` as
the entry point, which is defined more simply as:
void (*)(void *)
And then the `thread_create()` and `thread_create_named()` macros cast
the passed-in function point down to `thread_func_t`, that is, casting
away the `noreturn` attribute.
Clang considers casting between these two types to be invalid because
both the caller and the callee may have elided parts of the stack frame
save and restore, knowing that they won't be needed.
Recent Linux appears to be setting `-Wcast-function-type-strict`, which
causes this invalid cast to emit a warning, which with `-Werror` is
converted to an error, breaking the build.
This commit fixes this in the simplest possible way: adding `noreturn`
to the `thread_func_t` attribute. Since all our thread entry functions
already have this attribute, it's arguably a just a consistency fix
anyway.
I considered removing the casts in the macros, which silences the
warnings, but it turns out that Clang has a bug that won't emit this
error for implicit conversions, only explicit casts. So leaving them
there seems like a reasonable belt-and-suspenders approach. Also,
frankly, this whole mechanism seems a little undercooked inside LLVM, so
I'm content go with my intuition about the smallest, least invaisve
change.
**NOTE**: `__thread_create` is exported by `spl.ko` and has a
`thread_func_t` arg, so this is an ABI break. Whether that matters in
practice, I have no idea.
Further reading:
- llvm/llvm-project@1aad641
- llvm/llvm-project#7325
- llvm/llvm-project#41465
Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes openzfs#16672
Closes openzfs#16673
usaleem-ix
pushed a commit
to truenas/zfs
that referenced
this pull request
Oct 28, 2024
All of our thread entry functions have this signature:
void (*)(void*) __attribute__((noreturn))
The low-level `__thread_create()` function accepts a `thread_func_t` as
the entry point, which is defined more simply as:
void (*)(void *)
And then the `thread_create()` and `thread_create_named()` macros cast
the passed-in function point down to `thread_func_t`, that is, casting
away the `noreturn` attribute.
Clang considers casting between these two types to be invalid because
both the caller and the callee may have elided parts of the stack frame
save and restore, knowing that they won't be needed.
Recent Linux appears to be setting `-Wcast-function-type-strict`, which
causes this invalid cast to emit a warning, which with `-Werror` is
converted to an error, breaking the build.
This commit fixes this in the simplest possible way: adding `noreturn`
to the `thread_func_t` attribute. Since all our thread entry functions
already have this attribute, it's arguably a just a consistency fix
anyway.
I considered removing the casts in the macros, which silences the
warnings, but it turns out that Clang has a bug that won't emit this
error for implicit conversions, only explicit casts. So leaving them
there seems like a reasonable belt-and-suspenders approach. Also,
frankly, this whole mechanism seems a little undercooked inside LLVM, so
I'm content go with my intuition about the smallest, least invaisve
change.
**NOTE**: `__thread_create` is exported by `spl.ko` and has a
`thread_func_t` arg, so this is an ABI break. Whether that matters in
practice, I have no idea.
Further reading:
- llvm/llvm-project@1aad641
- llvm/llvm-project#7325
- llvm/llvm-project#41465
Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes openzfs#16672
Closes openzfs#16673
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Motivation and Context
Closes: #16672
Description
All of our thread entry functions have this signature:
The low-level
__thread_create()function accepts athread_func_tas the entry point, which is defined more simply as:And then the
thread_create()andthread_create_named()macros cast the passed-in function point down tothread_func_t, that is, casting away thenoreturnattribute.Clang considers casting between these two types to be invalid because both the caller and the callee may have elided parts of the stack frame save and restore, knowing that they won't be needed.
Recent Linux appears to be setting
-Wcast-function-type-strict, which causes this invalid cast to emit a warning, which with-Werroris converted to an error, breaking the build.This commit fixes this in the simplest possible way: adding
noreturnto thethread_func_tattribute. Since all our thread entry functions already have this attribute, it's arguably a just a consistency fixanyway.
I considered removing the casts in the macros, which silences the warnings, but it turns out that Clang has a bug that won't emit this error for implicit conversions, only explicit casts. So leaving them there seems like a reasonable belt-and suspenders approach. Also, frankly, this whole mechanism seems a little undercooked inside LLVM, so I'm content go with my intuition about the smallest, least invaisve change.
NOTE:
__thread_createis exported byspl.koand has athread_func_targ, so this is an ABI break. Whether that matters in practice, I have no idea.Further reading:
How Has This Been Tested?
Compile checked only:
Types of changes
Checklist:
Signed-off-by.