Re: [PATCH] Use SHLIB_COMPAT for libc symbols only if building libc.so

[Siddhesh Poyarekar <siddhesh at redhat dot com>]

On Tue, Mar 18, 2014 at 03:48:14PM -0700, Roland McGrath wrote:
> This seems worse to me.  I've been vaguely noodling about some centralized
> macro regime to make the NOT_IN_*/IS_IN_* cases #if-friendly.  Let's figure
> out what we want to do about those in general before considering
> SHLIB_COMPAT.  I tend to think that it's a more maintainable interface to
> have '#if SHLIB_COMPAT (libfoo, ...)' be a standalone test that encompasses
> the IS_IN_libfoo test (just as it encompasses the SHARED test).

The NOT_IN_libc definition (non-definition actually) is only used to
define IS_IN_libc in cases where there is no other IS_IN_*.  This can
be trivially used to set IS_IN_libc to 0 when NOT_IN_libc is set,
giving us the #if-friendly definition we want.

There is only one place (other than SHLIB_COMPAT) where IS_IN_libc is
used directly and I've fixed that up to use #if instead of #ifdef.

A further enhancement here would be to replace all uses of #ifdef
NOT_IN_libc with #if !IS_IN_libc so that NOT_IN_libc has just this one
specific usage.

I have avoided a warning on 'SHARED' by using ifdef on purpose for now
since it can be changed later if needed.

The generated code is identical before and after this change on
x86_64.

Siddhesh

	* include/shlib-compat.h: Define IS_IN_libc early.
	[NOT_IN_libc]: Define IS_IN_libc to 0.
	* nss/nss_files/files-parse.c: Include shlib-compat.h.
	[!ENTDATA]: Check for value of IS_IN_libc and not just if it
	is defined.

diff --git a/include/shlib-compat.h b/include/shlib-compat.h
index fac0814..3b6a227 100644
--- a/include/shlib-compat.h
+++ b/include/shlib-compat.h
@@ -23,6 +23,12 @@
 
 # include <abi-versions.h>
 
+# ifndef NOT_IN_libc
+#  define IS_IN_libc 1
+# else
+#  define IS_IN_libc 0
+# endif
+
 /* The file abi-versions.h (generated by scripts/abi-versions.awk) defines
    symbols like `ABI_libm_GLIBC_2_0' for each version set in the source
    code for each library.  For a version set that is subsumed by a later
@@ -45,10 +51,6 @@
    && (!(ABI_##lib##_##obsoleted - 0)					      \
        || ((ABI_##lib##_##introduced - 0) < (ABI_##lib##_##obsoleted - 0))))
 
-# ifndef NOT_IN_libc
-#  define IS_IN_libc 1
-# endif
-
 /* That header also defines symbols like `VERSION_libm_GLIBC_2_1' to
    the version set name to use for e.g. symbols first introduced into
    libm in the GLIBC_2.1 version.  Definitions of symbols with explicit
diff --git a/nss/nss_files/files-parse.c b/nss/nss_files/files-parse.c
index 1da1a6f..35a232c 100644
--- a/nss/nss_files/files-parse.c
+++ b/nss/nss_files/files-parse.c
@@ -21,6 +21,7 @@
 #include <string.h>
 #include <stdlib.h>
 #include <stdint.h>
+#include <shlib-compat.h>
 
 /* These symbols are defined by the including source file:
 
@@ -73,12 +74,12 @@ struct parser_data
 /* Export the line parser function so it can be used in nss_db.  */
 # define parser_stclass /* Global */
 # define parse_line CONCAT(_nss_files_parse_,ENTNAME)
-# ifdef IS_IN_libc
+# if defined SHARED && !IS_IN_libc
+#  define nss_files_parse_hidden_def(name) libnss_files_hidden_def (name)
+# else
 /* We are defining one of the functions that actually lives in libc
    because it is used to implement fget*ent and suchlike.  */
-#  define nss_files_parse_hidden_def(name) libc_hidden_def (name)
-# else
-#  define nss_files_parse_hidden_def(name) libnss_files_hidden_def (name)
+#   define nss_files_parse_hidden_def(name) libc_hidden_def (name)
 # endif
 #endif

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