From: Guenter Roeck <linux@roeck-us.net>
Add name of functions triggering warning backtraces to the __bug_table
object section to enable support for suppressing WARNING backtraces.
To limit image size impact, the pointer to the function name is only added
to the __bug_table section if both CONFIG_KUNIT_SUPPRESS_BACKTRACE and
CONFIG_DEBUG_BUGVERBOSE are enabled. Otherwise, the __func__ assembly
parameter is replaced with a (dummy) NULL parameter to avoid an image size
increase due to unused __func__ entries (this is necessary because __func__
is not a define but a virtual variable).
Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
---
arch/arm64/include/asm/asm-bug.h | 27 ++++++++++++++++++---------
arch/arm64/include/asm/bug.h | 8 +++++++-
2 files changed, 25 insertions(+), 10 deletions(-)
diff --git a/arch/arm64/include/asm/asm-bug.h b/arch/arm64/include/asm/asm-bug.h
index 6e73809f6492..bf0a5ba81611 100644
--- a/arch/arm64/include/asm/asm-bug.h
+++ b/arch/arm64/include/asm/asm-bug.h
@@ -8,37 +8,46 @@
#include <asm/brk-imm.h>
#ifdef CONFIG_DEBUG_BUGVERBOSE
-#define _BUGVERBOSE_LOCATION(file, line) __BUGVERBOSE_LOCATION(file, line)
-#define __BUGVERBOSE_LOCATION(file, line) \
+
+#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
+# define HAVE_BUG_FUNCTION
+# define __BUG_FUNC_PTR(func) .long func - .;
+#else
+# define __BUG_FUNC_PTR(func)
+#endif
+
+#define _BUGVERBOSE_LOCATION(file, func, line) __BUGVERBOSE_LOCATION(file, func, line)
+#define __BUGVERBOSE_LOCATION(file, func, line) \
.pushsection .rodata.str,"aMS",@progbits,1; \
14472: .string file; \
.popsection; \
\
.long 14472b - .; \
+ __BUG_FUNC_PTR(func) \
.short line;
#else
-#define _BUGVERBOSE_LOCATION(file, line)
+#define _BUGVERBOSE_LOCATION(file, func, line)
#endif
#ifdef CONFIG_GENERIC_BUG
-#define __BUG_ENTRY(flags) \
+#define __BUG_ENTRY(flags, func) \
.pushsection __bug_table,"aw"; \
.align 2; \
14470: .long 14471f - .; \
-_BUGVERBOSE_LOCATION(__FILE__, __LINE__) \
+_BUGVERBOSE_LOCATION(__FILE__, func, __LINE__) \
.short flags; \
.align 2; \
.popsection; \
14471:
#else
-#define __BUG_ENTRY(flags)
+#define __BUG_ENTRY(flags, func)
#endif
-#define ASM_BUG_FLAGS(flags) \
- __BUG_ENTRY(flags) \
+#define ASM_BUG_FLAGS(flags, func) \
+ __BUG_ENTRY(flags, func) \
brk BUG_BRK_IMM
-#define ASM_BUG() ASM_BUG_FLAGS(0)
+#define ASM_BUG() ASM_BUG_FLAGS(0, .)
#endif /* __ASM_ASM_BUG_H */
diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
index 28be048db3f6..044c5e24a17d 100644
--- a/arch/arm64/include/asm/bug.h
+++ b/arch/arm64/include/asm/bug.h
@@ -11,8 +11,14 @@
#include <asm/asm-bug.h>
+#ifdef HAVE_BUG_FUNCTION
+# define __BUG_FUNC __func__
+#else
+# define __BUG_FUNC NULL
+#endif
+
#define __BUG_FLAGS(flags) \
- asm volatile (__stringify(ASM_BUG_FLAGS(flags)));
+ asm volatile (__stringify(ASM_BUG_FLAGS(flags, %c0)) : : "i" (__BUG_FUNC));
#define BUG() do { \
__BUG_FLAGS(0); \
--
2.34.1On Thu, Mar 13, 2025 at 11:43:22AM +0000, Alessandro Carminati wrote: > diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h > index 28be048db3f6..044c5e24a17d 100644 > --- a/arch/arm64/include/asm/bug.h > +++ b/arch/arm64/include/asm/bug.h > @@ -11,8 +11,14 @@ > > #include <asm/asm-bug.h> > > +#ifdef HAVE_BUG_FUNCTION > +# define __BUG_FUNC __func__ > +#else > +# define __BUG_FUNC NULL > +#endif > + > #define __BUG_FLAGS(flags) \ > - asm volatile (__stringify(ASM_BUG_FLAGS(flags))); > + asm volatile (__stringify(ASM_BUG_FLAGS(flags, %c0)) : : "i" (__BUG_FUNC)); Why is 'i' the right asm constraint to use here? It seems a bit odd to use that for a pointer. Will
Hello Will,
On Thu, Mar 13, 2025 at 1:25 PM Will Deacon <will@kernel.org> wrote:
>
> On Thu, Mar 13, 2025 at 11:43:22AM +0000, Alessandro Carminati wrote:
> > diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
> > index 28be048db3f6..044c5e24a17d 100644
> > --- a/arch/arm64/include/asm/bug.h
> > +++ b/arch/arm64/include/asm/bug.h
> > @@ -11,8 +11,14 @@
> >
> > #include <asm/asm-bug.h>
> >
> > +#ifdef HAVE_BUG_FUNCTION
> > +# define __BUG_FUNC __func__
> > +#else
> > +# define __BUG_FUNC NULL
> > +#endif
> > +
> > #define __BUG_FLAGS(flags) \
> > - asm volatile (__stringify(ASM_BUG_FLAGS(flags)));
> > + asm volatile (__stringify(ASM_BUG_FLAGS(flags, %c0)) : : "i" (__BUG_FUNC));
>
> Why is 'i' the right asm constraint to use here? It seems a bit odd to
> use that for a pointer.
I received this code as legacy from a previous version.
In my review, I considered the case when HAVE_BUG_FUNCTION is defined:
Here, __BUG_FUNC is defined as __func__, which is the name of the
current function as a string literal.
Using the constraint "i" seems appropriate to me in this case.
However, when HAVE_BUG_FUNCTION is not defined:
__BUG_FUNC is defined as NULL. Initially, I considered it literal 0,
but after investigating your concern, I found:
```
$ echo -E "#include <stdio.h>\n#include <stddef.h>\nint main()
{\nreturn 0;\n}" | aarch64-linux-gnu-gcc -E -dM - | grep NULL
#define NULL ((void *)0)
```
I realized that NULL is actually a pointer that is not a link time
symbol, and using the "i" constraint with NULL may result in undefined
behavior.
Would the following alternative definition for __BUG_FUNC be more convincing?
```
#ifdef HAVE_BUG_FUNCTION
#define __BUG_FUNC __func__
#else
#define __BUG_FUNC (uintptr_t)0
#endif
```
Let me know your thoughts.
>
> Will
>
--
---
172
On Thu, Mar 13, 2025 at 05:40:59PM +0100, Alessandro Carminati wrote:
> On Thu, Mar 13, 2025 at 1:25 PM Will Deacon <will@kernel.org> wrote:
> >
> > On Thu, Mar 13, 2025 at 11:43:22AM +0000, Alessandro Carminati wrote:
> > > diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
> > > index 28be048db3f6..044c5e24a17d 100644
> > > --- a/arch/arm64/include/asm/bug.h
> > > +++ b/arch/arm64/include/asm/bug.h
> > > @@ -11,8 +11,14 @@
> > >
> > > #include <asm/asm-bug.h>
> > >
> > > +#ifdef HAVE_BUG_FUNCTION
> > > +# define __BUG_FUNC __func__
> > > +#else
> > > +# define __BUG_FUNC NULL
> > > +#endif
> > > +
> > > #define __BUG_FLAGS(flags) \
> > > - asm volatile (__stringify(ASM_BUG_FLAGS(flags)));
> > > + asm volatile (__stringify(ASM_BUG_FLAGS(flags, %c0)) : : "i" (__BUG_FUNC));
> >
> > Why is 'i' the right asm constraint to use here? It seems a bit odd to
> > use that for a pointer.
>
> I received this code as legacy from a previous version.
> In my review, I considered the case when HAVE_BUG_FUNCTION is defined:
> Here, __BUG_FUNC is defined as __func__, which is the name of the
> current function as a string literal.
> Using the constraint "i" seems appropriate to me in this case.
>
> However, when HAVE_BUG_FUNCTION is not defined:
> __BUG_FUNC is defined as NULL. Initially, I considered it literal 0,
> but after investigating your concern, I found:
>
> ```
> $ echo -E "#include <stdio.h>\n#include <stddef.h>\nint main()
> {\nreturn 0;\n}" | aarch64-linux-gnu-gcc -E -dM - | grep NULL
> #define NULL ((void *)0)
> ```
>
> I realized that NULL is actually a pointer that is not a link time
> symbol, and using the "i" constraint with NULL may result in undefined
> behavior.
>
> Would the following alternative definition for __BUG_FUNC be more convincing?
>
> ```
> #ifdef HAVE_BUG_FUNCTION
> #define __BUG_FUNC __func__
> #else
> #define __BUG_FUNC (uintptr_t)0
> #endif
> ```
> Let me know your thoughts.
Thanks for the analysis; I hadn't noticed this specific issue, it just
smelled a bit fishy. Anyway, the diff above looks better, thanks.
Will
Le 18/03/2025 à 16:59, Will Deacon a écrit :
> On Thu, Mar 13, 2025 at 05:40:59PM +0100, Alessandro Carminati wrote:
>> On Thu, Mar 13, 2025 at 1:25 PM Will Deacon <will@kernel.org> wrote:
>>>
>>> On Thu, Mar 13, 2025 at 11:43:22AM +0000, Alessandro Carminati wrote:
>>>> diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
>>>> index 28be048db3f6..044c5e24a17d 100644
>>>> --- a/arch/arm64/include/asm/bug.h
>>>> +++ b/arch/arm64/include/asm/bug.h
>>>> @@ -11,8 +11,14 @@
>>>>
>>>> #include <asm/asm-bug.h>
>>>>
>>>> +#ifdef HAVE_BUG_FUNCTION
>>>> +# define __BUG_FUNC __func__
>>>> +#else
>>>> +# define __BUG_FUNC NULL
>>>> +#endif
>>>> +
>>>> #define __BUG_FLAGS(flags) \
>>>> - asm volatile (__stringify(ASM_BUG_FLAGS(flags)));
>>>> + asm volatile (__stringify(ASM_BUG_FLAGS(flags, %c0)) : : "i" (__BUG_FUNC));
>>>
>>> Why is 'i' the right asm constraint to use here? It seems a bit odd to
>>> use that for a pointer.
>>
>> I received this code as legacy from a previous version.
>> In my review, I considered the case when HAVE_BUG_FUNCTION is defined:
>> Here, __BUG_FUNC is defined as __func__, which is the name of the
>> current function as a string literal.
>> Using the constraint "i" seems appropriate to me in this case.
>>
>> However, when HAVE_BUG_FUNCTION is not defined:
>> __BUG_FUNC is defined as NULL. Initially, I considered it literal 0,
>> but after investigating your concern, I found:
>>
>> ```
>> $ echo -E "#include <stdio.h>\n#include <stddef.h>\nint main()
>> {\nreturn 0;\n}" | aarch64-linux-gnu-gcc -E -dM - | grep NULL
>> #define NULL ((void *)0)
>> ```
>>
>> I realized that NULL is actually a pointer that is not a link time
>> symbol, and using the "i" constraint with NULL may result in undefined
>> behavior.
>>
>> Would the following alternative definition for __BUG_FUNC be more convincing?
>>
>> ```
>> #ifdef HAVE_BUG_FUNCTION
>> #define __BUG_FUNC __func__
>> #else
>> #define __BUG_FUNC (uintptr_t)0
>> #endif
>> ```
>> Let me know your thoughts.
>
> Thanks for the analysis; I hadn't noticed this specific issue, it just
> smelled a bit fishy. Anyway, the diff above looks better, thanks.
That propably deserves a comment.
Doesn't sparse and/or checkpatch complain about 0 being used in lieu of
NULL ?
By the way I had similar problem in the past with GCC not seeing NULL as
a __builtin_constant_p(), refer commit 1d8f739b07bd ("powerpc/kuap: Fix
set direction in allow/prevent_user_access()")
Christophe
On 3/19/25 01:05, Christophe Leroy wrote:
>
>
> Le 18/03/2025 à 16:59, Will Deacon a écrit :
>> On Thu, Mar 13, 2025 at 05:40:59PM +0100, Alessandro Carminati wrote:
>>> On Thu, Mar 13, 2025 at 1:25 PM Will Deacon <will@kernel.org> wrote:
>>>>
>>>> On Thu, Mar 13, 2025 at 11:43:22AM +0000, Alessandro Carminati wrote:
>>>>> diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
>>>>> index 28be048db3f6..044c5e24a17d 100644
>>>>> --- a/arch/arm64/include/asm/bug.h
>>>>> +++ b/arch/arm64/include/asm/bug.h
>>>>> @@ -11,8 +11,14 @@
>>>>>
>>>>> #include <asm/asm-bug.h>
>>>>>
>>>>> +#ifdef HAVE_BUG_FUNCTION
>>>>> +# define __BUG_FUNC __func__
>>>>> +#else
>>>>> +# define __BUG_FUNC NULL
>>>>> +#endif
>>>>> +
>>>>> #define __BUG_FLAGS(flags) \
>>>>> - asm volatile (__stringify(ASM_BUG_FLAGS(flags)));
>>>>> + asm volatile (__stringify(ASM_BUG_FLAGS(flags, %c0)) : : "i" (__BUG_FUNC));
>>>>
>>>> Why is 'i' the right asm constraint to use here? It seems a bit odd to
>>>> use that for a pointer.
>>>
>>> I received this code as legacy from a previous version.
>>> In my review, I considered the case when HAVE_BUG_FUNCTION is defined:
>>> Here, __BUG_FUNC is defined as __func__, which is the name of the
>>> current function as a string literal.
>>> Using the constraint "i" seems appropriate to me in this case.
>>>
>>> However, when HAVE_BUG_FUNCTION is not defined:
>>> __BUG_FUNC is defined as NULL. Initially, I considered it literal 0,
>>> but after investigating your concern, I found:
>>>
>>> ```
>>> $ echo -E "#include <stdio.h>\n#include <stddef.h>\nint main()
>>> {\nreturn 0;\n}" | aarch64-linux-gnu-gcc -E -dM - | grep NULL
>>> #define NULL ((void *)0)
>>> ```
>>>
>>> I realized that NULL is actually a pointer that is not a link time
>>> symbol, and using the "i" constraint with NULL may result in undefined
>>> behavior.
>>>
>>> Would the following alternative definition for __BUG_FUNC be more convincing?
>>>
>>> ```
>>> #ifdef HAVE_BUG_FUNCTION
>>> #define __BUG_FUNC __func__
>>> #else
>>> #define __BUG_FUNC (uintptr_t)0
>>> #endif
>>> ```
>>> Let me know your thoughts.
>>
>> Thanks for the analysis; I hadn't noticed this specific issue, it just
>> smelled a bit fishy. Anyway, the diff above looks better, thanks.
>
> That propably deserves a comment.
>
> Doesn't sparse and/or checkpatch complain about 0 being used in lieu of NULL ?
>
__BUG_FUNC is only used as parameter to asm code, not as pointer.
From the diff:
- : : "i" (__FILE__), "i" (__LINE__), \
+ : : "i" (__FILE__), "i" (__BUG_FUNC), "i" (__LINE__),\
The use is quite similar to __FILE__ and __LINE__. It might even be possible
and appropriate to just define __BUG_FUNC as 0 if HAVE_BUG_FUNCTION is not defined.
Guenter
On Wed, Mar 19, 2025 at 09:05:27AM +0100, Christophe Leroy wrote: > > Doesn't sparse and/or checkpatch complain about 0 being used in lieu of NULL > ? Sparse does have a "Using plain integer as NULL pointer" warning, yes. I can't apply this patchset and I haven't been following the conversation closely (plus I'm pretty stupid as well) so I'm not sure if it will trigger here... regards, dan carpenter
On 3/18/25 08:59, Will Deacon wrote:
> On Thu, Mar 13, 2025 at 05:40:59PM +0100, Alessandro Carminati wrote:
>> On Thu, Mar 13, 2025 at 1:25 PM Will Deacon <will@kernel.org> wrote:
>>>
>>> On Thu, Mar 13, 2025 at 11:43:22AM +0000, Alessandro Carminati wrote:
>>>> diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
>>>> index 28be048db3f6..044c5e24a17d 100644
>>>> --- a/arch/arm64/include/asm/bug.h
>>>> +++ b/arch/arm64/include/asm/bug.h
>>>> @@ -11,8 +11,14 @@
>>>>
>>>> #include <asm/asm-bug.h>
>>>>
>>>> +#ifdef HAVE_BUG_FUNCTION
>>>> +# define __BUG_FUNC __func__
>>>> +#else
>>>> +# define __BUG_FUNC NULL
>>>> +#endif
>>>> +
>>>> #define __BUG_FLAGS(flags) \
>>>> - asm volatile (__stringify(ASM_BUG_FLAGS(flags)));
>>>> + asm volatile (__stringify(ASM_BUG_FLAGS(flags, %c0)) : : "i" (__BUG_FUNC));
>>>
>>> Why is 'i' the right asm constraint to use here? It seems a bit odd to
>>> use that for a pointer.
>>
>> I received this code as legacy from a previous version.
>> In my review, I considered the case when HAVE_BUG_FUNCTION is defined:
>> Here, __BUG_FUNC is defined as __func__, which is the name of the
>> current function as a string literal.
>> Using the constraint "i" seems appropriate to me in this case.
>>
>> However, when HAVE_BUG_FUNCTION is not defined:
>> __BUG_FUNC is defined as NULL. Initially, I considered it literal 0,
>> but after investigating your concern, I found:
>>
>> ```
>> $ echo -E "#include <stdio.h>\n#include <stddef.h>\nint main()
>> {\nreturn 0;\n}" | aarch64-linux-gnu-gcc -E -dM - | grep NULL
>> #define NULL ((void *)0)
>> ```
>>
>> I realized that NULL is actually a pointer that is not a link time
>> symbol, and using the "i" constraint with NULL may result in undefined
>> behavior.
>>
>> Would the following alternative definition for __BUG_FUNC be more convincing?
>>
>> ```
>> #ifdef HAVE_BUG_FUNCTION
>> #define __BUG_FUNC __func__
>> #else
>> #define __BUG_FUNC (uintptr_t)0
>> #endif
>> ```
>> Let me know your thoughts.
>
> Thanks for the analysis; I hadn't noticed this specific issue, it just
> smelled a bit fishy. Anyway, the diff above looks better, thanks.
>
It has been a long time, but I seem to recall that I ran into trouble when
trying to use a different constraint.
Guenter
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