Move 'how this works' details from namespace.h to DETAILS

2 files changed, 136 insertions, 112 deletions

diff --git a/src/lib/libc/include/DETAILS b/src/lib/libc/include/DETAILS
new file mode 100644
index 0000000000..6382cc1c0d
--- /dev/null
+++ b/src/lib/libc/include/DETAILS
@@ -0,0 +1,133 @@
+The goal: calls from inside libc to other libc functions should
+ * not be overridable (except for the malloc family), and
+ * not have pointless inefficiencies.
+
+To achieve this, we arrange that all these internal call be via
+identifiers that are of hidden visibility and--to avoid confusion
+and work correctly in static executables--are in the reserved
+namespace.
+
+This document describes the details of the naming scheme and how
+it is implemented.
+
+I've chosen a prefix of underbar-libc-underbar ("_libc_") for this.
+These are not declared directly; instead, the gcc "asm labels"
+extension is used to rename the function.
+
+We need many of the symbols to be weak in *static* builds, but they
+can be strong in the dynamic library, as there's a natural precedence
+from the search order there.  When the descriptions below say a
+name is "weak", that is only necessary for the static library and
+not for the shared library.  Note: use defined(PIC) to recognize
+when compiling the shared objects: some archs define __PIC__ *all*
+the time.
+
+---------
+
+For syscalls which are not cancellation points, such as getpid(),
+the identifiers are just:
+        _libc_getpid            hidden alias, for use internal to libc only
+        _thread_sys_getpid      global name, for use outside libc only
+        getpid                  weak alias, for use outside libc only
+
+For syscalls which are cancellation points, such as wait4(), there
+are identifiers that do not provide cancellation:
+        _libc_wait4             hidden alias, for use internal to libc only
+        _thread_sys_wait4       global name, for use outside libc only
+...and identifiers that do provide cancellation:
+        wait4                   weak alias, for general use
+        _libc_wait4_cancel      hidden name, for use internal to libc only
+Inside libc, the bare name ("wait4") binds to the version *with*
+cancellation.  If it's necessary to use the syscall without doing
+cancellation it can be obtained by calling HIDDEN(x) instead of
+just x.
+
+Some other calls need to be wrapped for reasons other than cancellation,
+such as to provide functionality beyond the underlying syscall (e.g.,
+ptrace).  For these, there are identifiers for the raw call, without
+the wrapping:
+        _libc_ptrace            hidden alias, for use internal to libc only
+        _thread_sys_ptrace      global name, for use outside libc only
+...and identifiers that do provide the libc wrapping:
+        ptrace                  weak alias, for general use
+        _libc_ptrace_wrap       hidden name, for use internal to libc only
+Inside libc, the bare name ("ptrace") binds to the wrapper; if
+the raw version is necessary it can be obtained by calling HIDDEN(x)
+instead of just x.
+
+For syscalls implemented in ASM, the aliases of the raw syscall stub
+are provided by the ASM macros.  Of the macros used by sys/Makefile.inc:
+RSYSCALL(), PSEUDO(), and PSEUDO_NOERROR() generate all three names
+(ala getpid() above), while RSYSCALL_HIDDEN() generates just the
+_thread_sys_x and _libc_x names.
+
+
+
+By using gcc's "asm label" extension, we can usually avoid having
+to type those prefixes in the .h and .c files.  However, for those
+cases where a non-default binding is necessary we can use these macros
+to get the desired identifier:
+
+  CANCEL(x)
+        This expands to the internal, hidden name of a cancellation
+        wrapper: _libc_x_cancel.  ex: CANCEL(fsync)(fd)
+
+  WRAP(x)
+        This expands to the internal, hidden name of a non-cancellation
+        wrapper: _libc_x_wrap.  ex: WRAP(sigprocmask)(set)
+
+
+In order to actually set up the desired asm labels, we use these in
+the internal .h files:
+  PROTO_NORMAL(x)               Symbols used both internally and externally
+        This makes gcc convert use of x to use _libc_x instead
+        ex: PROTO_NORMAL(getpid)
+
+  PROTO_STD_DEPRECATED(x)       Standard C symbols that we don't want to use
+        This just marks the symbol as deprecated, with no renaming.
+        ex: PROTO_STD_DEPRECATED(strcpy)
+
+  PROTO_DEPRECATED(x)   Symbols not in ISO C that we don't want to use
+        This marks the symbol as both weak and deprecated, with no renaming
+        ex: PROTO_DEPRECATED(creat)
+
+  PROTO_CANCEL(x)               Functions that have cancellation wrappers
+        Like PROTO_NORMAL(x), but also declares _libc_x_cancel
+        ex: PROTO_CANCEL(wait4)
+
+  PROTO_WRAP(x)         Functions that have wrappers for other reasons
+        Like PROTO_NORMAL(x), but also declares _libc_x_wrap.  Internal
+        calls that want the wrapper's processing should invoke WRAP(x)(...)
+        ex: PROTO_WRAP(sigaction)
+
+
+Finally, to create the expected aliases, we use these in the .c files
+where the definitions are:
+  DEF_STRONG(x)         Symbols reserved to or specified by ISO C
+        This defines x as a strong alias for _libc_x; this must only
+        be used for symbols that are reserved by the C standard
+        (or reserved in the external identifier namespace).
+        Matches with PROTO_NORMAL()
+        ex: DEF_STRONG(fopen)
+
+  DEF_WEAK(x)           Symbols used internally and not in ISO C
+        This defines x as a weak alias for _libc_x
+        Matches with PROTO_NORMAL()
+        ex: DEF_WEAK(lseek)
+
+  DEF_CANCEL(x)         Symbols that have a cancellation wrapper
+        This defines x as a weak alias for _libc_x_cancel.
+        Matches with PROTO_CANCEL()
+        ex: DEF_CANCEL(read)
+
+  DEF_WRAP(x)
+        This defines x as a weak alias for _libc_x_wrap.
+        Matches with PROTO_WRAP()
+        ex: DEF_WRAP(ptrace)
+
+  MAKE_CLONE(dst, src)  Symbols that are exact clones of other symbols
+        This declares _libc_dst as being the same type as dst, and makes
+        _libc_dst a strong, hidden alias for _libc_src.  You still need to
+        DEF_STRONG(dst) or DEF_WEAK(dst) to alias dst itself
+        ex: MAKE_CLONE(SHA224Pad, SHA256Pad)
+
diff --git a/src/lib/libc/include/namespace.h b/src/lib/libc/include/namespace.h
index 60766afc0b..79692af0bc 100644
--- a/src/lib/libc/include/namespace.h
+++ b/src/lib/libc/include/namespace.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: namespace.h,v 1.12 2018/01/18 08:23:44 guenther Exp $ */
+/*      $OpenBSD: namespace.h,v 1.13 2019/05/13 20:00:32 guenther Exp $ */
 
 #ifndef _LIBC_NAMESPACE_H_
 #define _LIBC_NAMESPACE_H_
@@ -20,117 +20,8 @@
  */
 
 /*
- * The goal: calls from inside libc to other libc functions should be via
- * identifiers that are of hidden visibility and--to avoid confusion--are
- * in the reserved namespace.  By doing this these calls are protected
- * from overriding by applications and on many platforms can avoid creation
- * or use of GOT or PLT entries.  I've chosen a prefix of underbar-C-underbar
- * ("_libc_") for this.  These will not be declared directly; instead, the
- * gcc "asm labels" extension will be used rename the function.
- *
- * For syscalls which are cancellation points, such as wait4(), there
- * are identifiers that do not provide cancellation:
- *      _libc_wait4             hidden alias, for use internal to libc only
- *      _thread_sys_wait4       global name, for use outside libc only
- * ...and identifiers that do provide cancellation:
- *      wait4                   weak alias, for general use
- *      _libc_wait4_cancel      hidden alias, for use internal to libc only
- * Inside libc, the bare name ("wait4") binds to the version *without*
- * cancellation; the few times where cancellation is desired it can be
- * obtained by calling CANCEL(x) instead of just x.
- *
- * Some other calls need to be wrapped for reasons other than cancellation,
- * such as to provide functionality beyond the underlying syscall (e.g.,
- * sigaction).  For these, there are identifiers for the raw call, without
- * the wrapping:
- *      _libc_sigaction         hidden alias, for use internal to libc only
- *      _thread_sys_sigaction   global name, for use outside libc only
- * ...and identifiers that do provide the libc wrapping:
- *      sigaction               weak alias, for general use
- *      _libc_sigaction_wrap    hidden alias, for use internal to libc only
- * Inside libc, the bare name ("sigaction") binds to the wrapper; when the
- * raw version is necessary it can be obtained by calling HIDDEN(x) instead of
- * just x.
- *
- * For syscalls which are not cancellation points, such as getpid(),
- * the identifiers are just:
- *      _libc_getpid            hidden alias, for use internal to libc only
- *      _thread_sys_getpid      global name, for use outside libc only
- *      getpid                  weak alias, for use outside libc only
- *
- * By using gcc's "asm label" extension, we can usually avoid having
- * to type those prefixes in the .h and .c files.  However, for those
- * cases where a non-default binding is necessary we can use these macros
- * to get the desired identifier:
- *
- *   CANCEL(x)
- *      This expands to the internal, hidden name of a cancellation
- *      wrapper: _libc_x_cancel.  ex: CANCEL(fsync)(fd)
- *
- *   WRAP(x)
- *      This expands to the internal, hidden name of a non-cancellation
- *      wrapper: _libc_x_wrap.  ex: WRAP(sigprocmask)(set)
- *
- *
- * In order to actually set up the desired asm labels, we use these in
- * the internal .h files:
- *   PROTO_NORMAL(x)            Symbols used both internally and externally
- *      This makes gcc convert use of x to use _libc_x instead
- *      ex: PROTO_NORMAL(getpid)
- *
- *   PROTO_STD_DEPRECATED(x)    Standard C symbols that we don't want to use
- *      This just marks the symbol as deprecated, with no renaming.
- *      ex: PROTO_STD_DEPRECATED(strcpy)
- *
- *   PROTO_DEPRECATED(x)        Symbols not in ISO C that we don't want to use
- *      This marks the symbol as both weak and deprecated, with no renaming
- *      ex: PROTO_DEPRECATED(creat)
- *
- *   PROTO_CANCEL(x)            Functions that have cancellation wrappers
- *      Like PROTO_NORMAL(x), but also declares _libc_x_cancel
- *      ex: PROTO_CANCEL(wait4)
- *
- *   PROTO_WRAP(x)              Functions that have wrappers for other reasons
- *      Like PROTO_NORMAL(x), but also declares _libc_x_wrap.  Internal
- *      calls that want the wrapper's processing should invoke WRAP(x)(...)
- *      ex: PROTO_WRAP(sigaction)
- *
- *
- * Finally, to create the expected aliases, we use these in the .c files
- * where the definitions are:
- *   DEF_STRONG(x)              Symbols reserved to or specified by ISO C
- *      This defines x as a strong alias for _libc_x; this must only
- *      be used for symbols that are reserved by the C standard
- *      (or reserved in the external identifier namespace).
- *      Matches with PROTO_NORMAL()
- *      ex: DEF_STRONG(fopen)
- *
- *   DEF_WEAK(x)                Symbols used internally and not in ISO C
- *      This defines x as a weak alias for _libc_x
- *      Matches with PROTO_NORMAL()
- *      ex: DEF_WEAK(lseek)
- *
- *   DEF_CANCEL(x)              Symbols that have a cancellation wrapper
- *      This defines x as a weak alias for _libc_x_cancel.
- *      Matches with PROTO_CANCEL()
- *      ex: DEF_CANCEL(read)
- *
- *   DEF_WRAP(x)
- *      This defines x as a weak alias for _libc_x_wrap.
- *      Matches with PROTO_WRAP()
- *      ex: DEF_WRAP(sigaction)
- *
- *   DEF_SYS(x)
- *      This defines _thread_sys_x as a strong alias for _libc_x.  This should
- *      only be needed for syscalls that have C instead of asm stubs.
- *      Matches with PROTO_NORMAL(), PROTO_CANCEL(), or PROTO_WRAP()
- *      ex: DEF_SYS(pread)
- *
- *   MAKE_CLONE(dst, src)       Symbols that are exact clones of other symbols
- *      This declares _libc_dst as being the same type as dst, and makes
- *      _libc_dst a strong, hidden alias for _libc_src.  You still need to
- *      DEF_STRONG(dst) or DEF_WEAK(dst) to alias dst itself
- *      ex: MAKE_CLONE(SHA224Pad, SHA256Pad)
+ * For explanations of how to use these, see README
+ * For explanations of why we use them and how they work, see DETAILS
  */
 
 #include <sys/cdefs.h>  /* for __dso_hidden and __{weak,strong}_alias */