[gcc r12-3400] doc: BPF CO-RE documentation

[David Faust <dfaust@gcc.gnu.org>]

https://gcc.gnu.org/g:d9996ccb9414c1acaaaecf0803244fc018b5125d

commit r12-3400-gd9996ccb9414c1acaaaecf0803244fc018b5125d
Author: David Faust <david.faust@oracle.com>
Date:   Tue Aug 3 10:33:03 2021 -0700

    doc: BPF CO-RE documentation
    
    Document the new command line options (-mco-re and -mno-co-re), the new
    BPF target builtin (__builtin_preserve_access_index), and the new BPF
    target attribute (preserve_access_index) introduced with BPF CO-RE.
    
    gcc/ChangeLog:
    
            * doc/extend.texi (BPF Type Attributes) New node.
            Document new preserve_access_index attribute.
            Document new preserve_access_index builtin.
            * doc/invoke.texi: Document -mco-re and -mno-co-re options.

Diff:
---
 gcc/doc/extend.texi | 16 ++++++++++++++++
 gcc/doc/invoke.texi | 13 ++++++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 7fb22ed8063..31319f7dd08 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -8256,6 +8256,7 @@ attributes.
 * Common Type Attributes::
 * ARC Type Attributes::
 * ARM Type Attributes::
+* BPF Type Attributes::
 * MeP Type Attributes::
 * PowerPC Type Attributes::
 * x86 Type Attributes::
@@ -8830,6 +8831,17 @@ virtual table for @code{C} is not exported.  (You can use
 @code{__attribute__} instead of @code{__declspec} if you prefer, but
 most Symbian OS code uses @code{__declspec}.)
 
+@node BPF Type Attributes
+@subsection BPF Type Attributes
+
+@cindex @code{preserve_access_index} type attribute, BPF
+BPF Compile Once - Run Everywhere (CO-RE) support. When attached to a
+@code{struct} or @code{union} type definition, indicates that CO-RE
+relocation information should be generated for any access to a variable
+of that type. The behavior is equivalent to the programmer manually
+wrapping every such access with @code{__builtin_preserve_access_index}.
+
+
 @node MeP Type Attributes
 @subsection MeP Type Attributes
 
@@ -15467,6 +15479,10 @@ Load 16-bits from the @code{struct sk_buff} packet data pointed by the register
 Load 32-bits from the @code{struct sk_buff} packet data pointed by the register @code{%r6} and return it.
 @end deftypefn
 
+@deftypefn {Built-in Function} void * __builtin_preserve_access_index (@var{expr})
+BPF Compile Once-Run Everywhere (CO-RE) support. Instruct GCC to generate CO-RE relocation records for any accesses to aggregate data structures (struct, union, array types) in @var{expr}. This builtin is otherwise transparent, the return value is whatever @var{expr} evaluates to. It is also overloaded: @var{expr} may be of any type (not necessarily a pointer), the return type is the same. Has no effect if @code{-mco-re} is not in effect (either specified or implied).
+@end deftypefn
+
 @node FR-V Built-in Functions
 @subsection FR-V Built-in Functions
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index a9580a08a65..e39dde009ef 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -904,7 +904,7 @@ Objective-C and Objective-C++ Dialects}.
 
 @emph{eBPF Options}
 @gccoptlist{-mbig-endian -mlittle-endian -mkernel=@var{version}
--mframe-limit=@var{bytes} -mxbpf}
+-mframe-limit=@var{bytes} -mxbpf -mco-re -mno-co-re}
 
 @emph{FR30 Options}
 @gccoptlist{-msmall-model  -mno-lsim}
@@ -22635,6 +22635,17 @@ Generate code for a big-endian target.
 @opindex mlittle-endian
 Generate code for a little-endian target.  This is the default.
 
+@item -mco-re
+@opindex mco-re
+Enable BPF Compile Once - Run Everywhere (CO-RE) support. Requires and
+is implied by @option{-gbtf}.
+
+@item -mno-co-re
+@opindex mno-co-re
+Disable BPF Compile Once - Run Everywhere (CO-RE) support. BPF CO-RE
+support is enabled by default when generating BTF debug information for
+the BPF target.
+
 @item -mxbpf
 Generate code for an expanded version of BPF, which relaxes some of
 the restrictions imposed by the BPF architecture: