[PATCH] Use __builtin_trap() for abort() if inhibit_libc

[PATCH] Use __builtin_trap() for abort() if inhibit_libc

[Sebastian Huber]

abort() is used in gcc_assert() and gcc_unreachable() which is used by target
libraries such as libgcov.a.  This patch changes the abort() definition under
certain conditions.  If inhibit_libc is defined and abort is not already
defined, then abort() is defined to __builtin_trap().

The inhibit_libc define is usually defined if GCC is built for targets running
in embedded systems which may optionally use a C standard library.  If
inhibit_libc is defined, then there may be still a full featured abort()
available.  abort() is a heavy weight function which depends on signals and
file streams.  For statically linked applications, this means that a dependency
on gcc_assert() pulls in the support for signals and file streams.  This could
prevent using gcov to test low end targets for example.  Using __builtin_trap()
avoids these dependencies if the target implements a "trap" instruction.  The
application or operating system could use a trap handler to react to failed GCC
runtime checks which caused a trap.

gcc/

	* tsystem.h (abort): Define abort() if inhibit_libc is defined and it
	is not already defined.
---
 gcc/tsystem.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/tsystem.h b/gcc/tsystem.h
index e1e6a96a4f48..5c72c69ff3ed 100644
--- a/gcc/tsystem.h
+++ b/gcc/tsystem.h
@@ -59,7 +59,7 @@ extern int atexit (void (*)(void));
 #endif
 
 #ifndef abort
-extern void abort (void) __attribute__ ((__noreturn__));
+#define abort() __builtin_trap ()
 #endif
 
 #ifndef strlen
-- 
2.26.2

Re: [PATCH] Use __builtin_trap() for abort() if inhibit_libc

[Jeff Law]

On 8/17/2021 2:41 AM, Sebastian Huber wrote:
> abort() is used in gcc_assert() and gcc_unreachable() which is used by target
> libraries such as libgcov.a.  This patch changes the abort() definition under
> certain conditions.  If inhibit_libc is defined and abort is not already
> defined, then abort() is defined to __builtin_trap().
>
> The inhibit_libc define is usually defined if GCC is built for targets running
> in embedded systems which may optionally use a C standard library.  If
> inhibit_libc is defined, then there may be still a full featured abort()
> available.  abort() is a heavy weight function which depends on signals and
> file streams.  For statically linked applications, this means that a dependency
> on gcc_assert() pulls in the support for signals and file streams.  This could
> prevent using gcov to test low end targets for example.  Using __builtin_trap()
> avoids these dependencies if the target implements a "trap" instruction.  The
> application or operating system could use a trap handler to react to failed GCC
> runtime checks which caused a trap.
>
> gcc/
>
> 	* tsystem.h (abort): Define abort() if inhibit_libc is defined and it
> 	is not already defined.
OK.
Jeff

Re: [PATCH] Use __builtin_trap() for abort() if inhibit_libc

[Christophe Lyon]

Hi,


On Tue, Aug 17, 2021 at 10:43 AM Sebastian Huber <
sebastian.huber@embedded-brains.de> wrote:

> abort() is used in gcc_assert() and gcc_unreachable() which is used by
> target
> libraries such as libgcov.a.  This patch changes the abort() definition
> under
> certain conditions.  If inhibit_libc is defined and abort is not already
> defined, then abort() is defined to __builtin_trap().
>
> The inhibit_libc define is usually defined if GCC is built for targets
> running
> in embedded systems which may optionally use a C standard library.  If
> inhibit_libc is defined, then there may be still a full featured abort()
> available.  abort() is a heavy weight function which depends on signals and
> file streams.  For statically linked applications, this means that a
> dependency
> on gcc_assert() pulls in the support for signals and file streams.  This
> could
> prevent using gcov to test low end targets for example.  Using
> __builtin_trap()
> avoids these dependencies if the target implements a "trap" instruction.
> The
> application or operating system could use a trap handler to react to
> failed GCC
> runtime checks which caused a trap.
>
> gcc/
>
>         * tsystem.h (abort): Define abort() if inhibit_libc is defined and
> it
>         is not already defined.
>


This causes a build failure on arm:
In file included from /libgcc/config/arm/unwind-arm.c:144:
/libgcc/unwind-arm-common.inc:55:24: error: macro "abort" passed 1
arguments, but takes just 0
   55 | extern void abort (void);

This small patch should fix it:
 diff --git a/libgcc/unwind-arm-common.inc b/libgcc/unwind-arm-common.inc
index c9b70c10d4f..77ec02ec811 100644
--- a/libgcc/unwind-arm-common.inc
+++ b/libgcc/unwind-arm-common.inc
@@ -50,10 +50,6 @@
 #define ARM_SIGCONTEXT_R0              0xc
 #endif

-/* We add a prototype for abort here to avoid creating a dependency on
-   target headers.  */
-extern void abort (void);
-
 /* Definitions for C++ runtime support routines.  We make these weak
    declarations to avoid pulling in libsupc++ unnecessarily.  */
 typedef unsigned char bool;


Christophe



> ---
>  gcc/tsystem.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gcc/tsystem.h b/gcc/tsystem.h
> index e1e6a96a4f48..5c72c69ff3ed 100644
> --- a/gcc/tsystem.h
> +++ b/gcc/tsystem.h
> @@ -59,7 +59,7 @@ extern int atexit (void (*)(void));
>  #endif
>
>  #ifndef abort
> -extern void abort (void) __attribute__ ((__noreturn__));
> +#define abort() __builtin_trap ()
>  #endif
>
>  #ifndef strlen
> --
> 2.26.2
>
>

Re: [PATCH] Use __builtin_trap() for abort() if inhibit_libc

[Sebastian Huber]

Hello Christophe,

it seems there are a couple of more abort() declarations:

libgcc/unwind-arm-common.inc:extern void abort (void);
libgcc/config/c6x/pr-support.c:extern void abort (void);
libgcc/config/arm/pr-support.c:extern void abort (void);
libgcc/config/arm/linux-atomic-64bit.c:extern void abort (void);
libgcc/fp-bit.c:   external to abort if abort is not used by the 
function, and the stubs
libgcc/fp-bit.c:extern void abort (void);

I will prepare a patch.

-- 
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Herr Sebastian HUBER
Dornierstr. 4
82178 Puchheim
Germany
email: sebastian.huber@embedded-brains.de
phone: +49-89-18 94 741 - 16
fax:   +49-89-18 94 741 - 08

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Re: [PATCH] Use __builtin_trap() for abort() if inhibit_libc

[Richard Biener]

On Mon, Aug 30, 2021 at 12:55 PM Sebastian Huber
<sebastian.huber@embedded-brains.de> wrote:
>
> Hello Christophe,
>
> it seems there are a couple of more abort() declarations:
>
> libgcc/unwind-arm-common.inc:extern void abort (void);
> libgcc/config/c6x/pr-support.c:extern void abort (void);
> libgcc/config/arm/pr-support.c:extern void abort (void);
> libgcc/config/arm/linux-atomic-64bit.c:extern void abort (void);
> libgcc/fp-bit.c:   external to abort if abort is not used by the
> function, and the stubs
> libgcc/fp-bit.c:extern void abort (void);
>
> I will prepare a patch.

Less likley to break might be to simply wrap 'abort'
in parentheses to avoid macro expansion?

> --
> embedded brains GmbH
> Herr Sebastian HUBER
> Dornierstr. 4
> 82178 Puchheim
> Germany
> email: sebastian.huber@embedded-brains.de
> phone: +49-89-18 94 741 - 16
> fax:   +49-89-18 94 741 - 08
>
> Registergericht: Amtsgericht München
> Registernummer: HRB 157899
> Vertretungsberechtigte Geschäftsführer: Peter Rasmussen, Thomas Dörfler
> Unsere Datenschutzerklärung finden Sie hier:
> https://embedded-brains.de/datenschutzerklaerung/

Re: [PATCH] Use __builtin_trap() for abort() if inhibit_libc

[Sebastian Huber]

On 30/08/2021 13:44, Richard Biener wrote:
> On Mon, Aug 30, 2021 at 12:55 PM Sebastian Huber
> <sebastian.huber@embedded-brains.de>  wrote:
>> Hello Christophe,
>>
>> it seems there are a couple of more abort() declarations:
>>
>> libgcc/unwind-arm-common.inc:extern void abort (void);
>> libgcc/config/c6x/pr-support.c:extern void abort (void);
>> libgcc/config/arm/pr-support.c:extern void abort (void);
>> libgcc/config/arm/linux-atomic-64bit.c:extern void abort (void);
>> libgcc/fp-bit.c:   external to abort if abort is not used by the
>> function, and the stubs
>> libgcc/fp-bit.c:extern void abort (void);
>>
>> I will prepare a patch.
> Less likley to break might be to simply wrap 'abort'
> in parentheses to avoid macro expansion?

I think the abort declaration in libgcc/unwind-arm-common.inc is the 
only problematic spot since unwind-arm-common.inc includes tsystem.h.

-- 
embedded brains GmbH
Herr Sebastian HUBER
Dornierstr. 4
82178 Puchheim
Germany
email: sebastian.huber@embedded-brains.de
phone: +49-89-18 94 741 - 16
fax:   +49-89-18 94 741 - 08

Registergericht: Amtsgericht München
Registernummer: HRB 157899
Vertretungsberechtigte Geschäftsführer: Peter Rasmussen, Thomas Dörfler
Unsere Datenschutzerklärung finden Sie hier:
https://embedded-brains.de/datenschutzerklaerung/

Re: [PATCH] Use __builtin_trap() for abort() if inhibit_libc

[Andrew Pinski]

On Tue, Aug 17, 2021 at 1:43 AM Sebastian Huber
<sebastian.huber@embedded-brains.de> wrote:
>
> abort() is used in gcc_assert() and gcc_unreachable() which is used by target
> libraries such as libgcov.a.  This patch changes the abort() definition under
> certain conditions.  If inhibit_libc is defined and abort is not already
> defined, then abort() is defined to __builtin_trap().
>
> The inhibit_libc define is usually defined if GCC is built for targets running
> in embedded systems which may optionally use a C standard library.  If
> inhibit_libc is defined, then there may be still a full featured abort()
> available.  abort() is a heavy weight function which depends on signals and
> file streams.  For statically linked applications, this means that a dependency
> on gcc_assert() pulls in the support for signals and file streams.  This could
> prevent using gcov to test low end targets for example.  Using __builtin_trap()
> avoids these dependencies if the target implements a "trap" instruction.  The
> application or operating system could use a trap handler to react to failed GCC
> runtime checks which caused a trap.

This also breaks sometimes compiling of emutls.c on some targets like uclibc ...
See https://gcc.gnu.org/PR110775 for some more details there.

Thanks,
Andrew

>
> gcc/
>
>         * tsystem.h (abort): Define abort() if inhibit_libc is defined and it
>         is not already defined.
> ---
>  gcc/tsystem.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gcc/tsystem.h b/gcc/tsystem.h
> index e1e6a96a4f48..5c72c69ff3ed 100644
> --- a/gcc/tsystem.h
> +++ b/gcc/tsystem.h
> @@ -59,7 +59,7 @@ extern int atexit (void (*)(void));
>  #endif
>
>  #ifndef abort
> -extern void abort (void) __attribute__ ((__noreturn__));
> +#define abort() __builtin_trap ()
>  #endif
>
>  #ifndef strlen
> --
> 2.26.2
>