Module Name: src
Committed By: riastradh
Date: Fri Mar 20 13:26:51 UTC 2015
Modified Files:
src/lib/libc: README
Log Message:
Elaborate on how our ad-hack symbol versioning works. Tweak style.
To generate a diff of this commit:
cvs rdiff -u -r1.1 -r1.2 src/lib/libc/README
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/lib/libc/README
diff -u src/lib/libc/README:1.1 src/lib/libc/README:1.2
--- src/lib/libc/README:1.1 Fri Mar 20 12:57:48 2015
+++ src/lib/libc/README Fri Mar 20 13:26:51 2015
@@ -1,4 +1,4 @@
- $NetBSD: README,v 1.1 2015/03/20 12:57:48 riastradh Exp $
+ $NetBSD: README,v 1.2 2015/03/20 13:26:51 riastradh Exp $
libc: The C library.
@@ -56,16 +56,14 @@ create the ELF weak symbol alias.
`_consttime_memequal'.
If a library routine is internal to libc, it is defined as an ELF
-global symbol with an underscore prefix.
-
-Its name is declared in the appropriate internal header file.
+global symbol with an underscore prefix. Its name is declared in the
+appropriate internal header file.
=> Example: For the internal library routine _initdir, used by the
implementations of opendir and rewinddir, libc defines a global
- symbol `_initdir'.
-
- The name `_initdir' is declared normally in
- src/lib/libc/gen/dirent_private.h.
+ symbol `_initdir'. The name `_initdir' is declared normally in
+ src/lib/libc/gen/dirent_private.h, and defined normally in
+ src/lib/libc/gen/initdir.c.
If the signature or semantics of a library routine foo changed in (for
example) NetBSD 6.0, then libc provides
@@ -100,7 +98,7 @@ compiled with the old signature, will co
(2) the ELF weak symbol `time' aliasing `_time', and
(3) the ELF global symbol `__time50' implementing the new signature.
- The header file <time.h> declares
+ The header file <time.h> (src/include/time.h) declares
time_t time(time_t *) __RENAME(__time50);
@@ -108,3 +106,38 @@ compiled with the old signature, will co
use the __time50 symbol from libc. However, old programs that were
compiled against the 32-bit declaration will continue to use the
32-bit symbol from libc.
+
+ The header file "namespace.h" (src/lib/libc/include/namespace.h)
+ defines `time' as a macro expanding to `_time'.
+
+ The source file src/lib/libc/gen/time.c includes "namespace.h" and
+ <time.h> and defines `time' normally. The declaration of `time' in
+ <time.h> is replaced after macro expansion by a declaration of
+ `_time', and the definition in time.c is replaced by a definition of
+ `_time'. But the __RENAME directive causes the resulting ELF global
+ symbol to be `__time50'.
+
+ The header file <compat/include/time.h>
+ (src/lib/libc/compat/include/time.h) declares
+
+ int32_t time(int32_t *);
+
+ The source file src/lib/libc/compat/gen/compat_time.c includes
+ "namespace.h", <compat/include/time.h>, and <time.h>, but suppresses
+ the normal declaration of `time' in <time.h> by defining
+ __LIBC12_SOURCE__. Then compat_time.c defines `time' normally.
+ Again, the name is replaced after macro expansion by `_time', but
+ since there is no __RENAME directive in <compat/include/time.h>, the
+ resulting ELF global symbol is `_time'.
+
+ Finally, alongside the definition in compat_time.c is
+
+ __weak_alias(time,_time)
+
+ to provide `time' as an ELF weak symbol aliasing `_time'.
+
+ The net effect is that NetBSD 6's libc provides the same definitions
+ as NetBSD 5's libc for the symbols `time' and `_time', so that old
+ programs that were compiled in NetBSD 5 will continue to work with
+ NetBSD 6's libc. But programs compiled in NetBSD 6 will have 64-bit
+ time_t.
