Re: [PATCH libaio v2 03/10] Use new symver function attribute to support LTO builds

Guillem Jover <[email protected]> writes:

> From: Guillem Jover <[email protected]>
>
> The LTO support cannot work properly when there are versioned symbols
> via asm statements, as those are not seen by the compiler. Use the new
> function attributes if supported instead of the asm statements.
>
> We need to move the SYMVER calls after the function definitions
> otherwise it will reference symbols not yet seen.
>

There is likely to be very little benefit from LTO for this library.
What's the motivation for this patch?

-Jeff

> Signed-off-by: Guillem Jover <[email protected]>
> ---
>  src/compat-0_1.c |  7 +++----
>  src/syscall.h    | 13 +++++++++++++
>  2 files changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/src/compat-0_1.c b/src/compat-0_1.c
> index 722e107..ac40fcc 100644
> --- a/src/compat-0_1.c
> +++ b/src/compat-0_1.c
> @@ -28,7 +28,6 @@
>  
>  
>  /* ABI change.  Provide partial compatibility on this one for now. */
> -SYMVER(compat0_1_io_cancel, io_cancel, 0.1);
>  int compat0_1_io_cancel(io_context_t ctx, struct iocb *iocb)
>  {
>  	struct io_event event;
> @@ -36,8 +35,8 @@ int compat0_1_io_cancel(io_context_t ctx, struct iocb *iocb)
>  	/* FIXME: the old ABI would return the event on the completion queue */
>  	return io_cancel(ctx, iocb, &event);
>  }
> +SYMVER(compat0_1_io_cancel, io_cancel, 0.1);
>  
> -SYMVER(compat0_1_io_queue_wait, io_queue_wait, 0.1);
>  int compat0_1_io_queue_wait(io_context_t ctx, struct timespec *when)
>  {
>  	struct timespec timeout;
> @@ -45,10 +44,10 @@ int compat0_1_io_queue_wait(io_context_t ctx, struct timespec *when)
>  		timeout = *when;
>  	return io_getevents(ctx, 0, 0, NULL, when ? &timeout : NULL);
>  }
> +SYMVER(compat0_1_io_queue_wait, io_queue_wait, 0.1);
>  
>  
>  /* ABI change.  Provide backwards compatibility for this one. */
> -SYMVER(compat0_1_io_getevents, io_getevents, 0.1);
>  int compat0_1_io_getevents(io_context_t ctx, long nr,
>  		       struct io_event *events,
>  		       const struct timespec *const_timeout)
> @@ -59,4 +58,4 @@ int compat0_1_io_getevents(io_context_t ctx, long nr,
>  	return io_getevents(ctx, 1, nr, events,
>  			const_timeout ? &timeout : NULL);
>  }
> -
> +SYMVER(compat0_1_io_getevents, io_getevents, 0.1);
> diff --git a/src/syscall.h b/src/syscall.h
> index f7ce979..59e0bb3 100644
> --- a/src/syscall.h
> +++ b/src/syscall.h
> @@ -2,14 +2,27 @@
>  #include <unistd.h>
>  #include <errno.h>
>  
> +#ifndef __has_attribute
> +#define __has_attribute(x) 0
> +#endif
> +
>  #define _SYMSTR(str)	#str
>  #define SYMSTR(str)	_SYMSTR(str)
>  
> +#if __has_attribute(__symver__)
> +#define SYMVER(compat_sym, orig_sym, ver_sym)	\
> +	extern __typeof(compat_sym) compat_sym \
> +	  __attribute__((__symver__(SYMSTR(orig_sym) "@LIBAIO_" SYMSTR(ver_sym))))
> +#define DEFSYMVER(compat_sym, orig_sym, ver_sym)	\
> +	extern __typeof(compat_sym) compat_sym \
> +	  __attribute__((__symver__(SYMSTR(orig_sym) "@@LIBAIO_" SYMSTR(ver_sym))))
> +#else
>  #define SYMVER(compat_sym, orig_sym, ver_sym)	\
>  	__asm__(".symver " SYMSTR(compat_sym) "," SYMSTR(orig_sym) "@LIBAIO_" SYMSTR(ver_sym))
>  
>  #define DEFSYMVER(compat_sym, orig_sym, ver_sym)	\
>  	__asm__(".symver " SYMSTR(compat_sym) "," SYMSTR(orig_sym) "@@LIBAIO_" SYMSTR(ver_sym))
> +#endif
>  
>  #if defined(__i386__)
>  #include "syscall-i386.h"


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