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From: Andreas Schwab <schwab@suse.de>
To: "Maciej W. Rozycki" <macro@mips.com>
Cc: <libc-alpha@sourceware.org>,  "H.J. Lu" <hjl.tools@gmail.com>,  Alan Modra <amodra@gmail.com>,  "Cary Coutant" <ccoutant@gmail.com>
Subject: Re: [PATCH 1/2] elf: Unify symbol address run-time calculation [BZ #19818]
References: <alpine.DEB.2.00.1802191042010.3553@tp.orcam.me.uk>
	<alpine.DEB.2.00.1802191059150.3553@tp.orcam.me.uk>
X-Yow: LOU GRANT froze my ASSETS!!
Date: Mon, 19 Feb 2018 16:14:00 -0000
In-Reply-To: <alpine.DEB.2.00.1802191059150.3553@tp.orcam.me.uk> (Maciej
	W. Rozycki's message of "Mon, 19 Feb 2018 13:31:07 +0000")
Message-ID: <mvmsh9xqego.fsf@suse.de>
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On Feb 19 2018, "Maciej W. Rozycki" <macro@mips.com> wrote:

> Index: glibc/sysdeps/generic/ldsodefs.h
> ===================================================================
> --- glibc.orig/sysdeps/generic/ldsodefs.h	2018-02-16 20:46:56.455844235 +0000
> +++ glibc/sysdeps/generic/ldsodefs.h	2018-02-16 20:54:43.029923370 +0000
> @@ -66,14 +66,20 @@ __BEGIN_DECLS
>  /* Result of the lookup functions and how to retrieve the base address.  */
>  typedef struct link_map *lookup_t;
>  #define LOOKUP_VALUE(map) map
> -#define LOOKUP_VALUE_ADDRESS(map) ((map) ? (map)->l_addr : 0)
> +#define LOOKUP_VALUE_ADDRESS(map, set) ((set) || (map) ? (map)->l_addr : 0)
> +
> +/* Calculate the address of symbol REF using the base address from map MAP,
> +   if non-NULL.  Don't check for NULL map if MAP_SET is TRUE.  */
> +#define SYMBOL_ADDRESS(map, ref, map_set)				\
> +  ((ref) == NULL ? 0							\
> +   : LOOKUP_VALUE_ADDRESS ((map), (map_set)) + (ref)->st_value)

No need for double parens, since uses of arguments must already be
properly parenthesized.

>  /* On some architectures a pointer to a function is not just a pointer
>     to the actual code of the function but rather an architecture
>     specific descriptor. */
>  #ifndef ELF_FUNCTION_PTR_IS_SPECIAL
>  # define DL_SYMBOL_ADDRESS(map, ref) \
> - (void *) (LOOKUP_VALUE_ADDRESS (map) + ref->st_value)
> + (void *) SYMBOL_ADDRESS ((map), (ref), false)

Likewise.

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."