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doc: BPF CO-RE documentation

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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.
This commit is contained in:
David Faust 2021-08-03 10:33:03 -07:00
parent f4cdfd4856
commit d9996ccb94
2 changed files with 28 additions and 1 deletions
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16
gcc/doc/extend.texi
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@ -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

13
gcc/doc/invoke.texi
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@ -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: