[PATCH v6] cacheflush.2: Document __builtin___clear_cache() as a more portable alternative

[Alejandro Colomar <alx.manpages@gmail.com>]

Reported-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
Cc: Martin Sebor <msebor@redhat.com>
Cc: Dave Martin <Dave.Martin@arm.com>
---

v6:
- GCC has always exposed 'void *', as Martin Sebor noted.
  It's Clang (and maybe others) that (following GCC's docs)
  exposed 'char *'.

 man2/cacheflush.2 | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/man2/cacheflush.2 b/man2/cacheflush.2
index aba625721..7a2eed506 100644
--- a/man2/cacheflush.2
+++ b/man2/cacheflush.2
@@ -86,6 +86,30 @@ On Linux, this call first appeared on the MIPS architecture,
 but nowadays, Linux provides a
 .BR cacheflush ()
 system call on some other architectures, but with different arguments.
+.SH NOTES
+Unless you need the finer grained control that this system call provides,
+you probably want to use the GCC built-in function
+.BR __builtin___clear_cache (),
+which provides a portable interface
+across platforms supported by GCC and compatible compilers:
+.PP
+.in +4n
+.EX
+.BI "void __builtin___clear_cache(void *" begin ", void *" end );
+.EE
+.in
+.PP
+On platforms that don't require instruction cache flushes,
+.BR __builtin___clear_cache ()
+has no effect.
+.PP
+.IR Note :
+On some GCC-compatible compilers,
+the prototype for this built-in function uses
+.I char *
+instead of
+.I void *
+for the parameters.
 .SH BUGS
 Linux kernels older than version 2.6.11 ignore the
 .I addr
-- 
2.29.2