On 4/25/23 11:35 AM, Stanislav Fomichev wrote:
On Tue, Apr 25, 2023 at 11:29 AM Yonghong Song <yhs@xxxxxxxx> wrote:
On 4/25/23 11:22 AM, Stanislav Fomichev wrote:
On Tue, Apr 25, 2023 at 11:10 AM Yonghong Song <yhs@xxxxxxxx> wrote:
On 4/25/23 10:04 AM, Stanislav Fomichev wrote:
On Mon, Apr 24, 2023 at 6:56 PM Yonghong Song <yhs@xxxxxxxx> wrote:
On 4/24/23 5:01 PM, Stanislav Fomichev wrote:
From: Peng Wei <pengweiprc@xxxxxxxxxx>
Compiling C++ BPF programs with existing bpf_helper_defs.h is not
Just curious, why you want to compile BPF programs with C++?
The patch looks good to me. But it would be great to know
some reasoning since a lot of stuff, e.g., some CORE related
intrinsics, not available for C++.
Can you share more? What's not available? Any pointers to the docs maybe?
Sorry, it is an attribute, instead of instrinsics.
The attribute preserve_access_index/btf_type_tag/btf_decl_tag are all C
only.
Interesting, thanks! I don't think we use btf_type_tag/btf_decl_tag in
the program we want to try c++, but losing preserve_access_index might
be unfortunate :-( But we'll see..
Btw, any reason these are explicitly opted out from c++? Doesn't seem
like there is anything c-specific in them?
Initial use case is C only. If we say to support C++, we will
need to add attribute processing codes in various other places
(member functions, templates, other c++ constructs, etc.)
to convert these attributes to proper debuginfo. There are no use
cases for this, so we didn't do it in the first place.
The c++ we are talking about here is mostly "c with classes +
templates"; no polymorphism / inheritance.
In llvm-project/clang/include/clang/Basic/Attr.td:
def BPFPreserveAccessIndex : InheritableAttr,
TargetSpecificAttr<TargetBPF> {
let Spellings = [Clang<"preserve_access_index">];
let Subjects = SubjectList<[Record], ErrorDiag>;
let Documentation = [BPFPreserveAccessIndexDocs];
let LangOpts = [COnly];
}
def BTFDeclTag : InheritableAttr {
let Spellings = [Clang<"btf_decl_tag">];
let Args = [StringArgument<"BTFDeclTag">];
let Subjects = SubjectList<[Var, Function, Record, Field, TypedefName],
ErrorDiag>;
let Documentation = [BTFDeclTagDocs];
let LangOpts = [COnly];
}
def BTFTypeTag : TypeAttr {
let Spellings = [Clang<"btf_type_tag">];
let Args = [StringArgument<"BTFTypeTag">];
let Documentation = [BTFTypeTagDocs];
let LangOpts = [COnly];
}
People here want to try to use c++ to see if templating helps with v4
vs v6 handling.
We have a bunch of copy-paste around this place and would like to see
whether c++ could make it a bit more readable.
possible due to stricter C++ type conversions. C++ complains
about (void *) type conversions:
bpf_helper_defs.h:57:67: error: invalid conversion from ‘void*’ to ‘void* (*)(void*, const void*)’ [-fpermissive]
57 | static void *(*bpf_map_lookup_elem)(void *map, const void *key) = (void *) 1;
| ^~~~~~~~~~
| |
| void*
Extend bpf_doc.py to use proper function type instead of void.
Could you specify what exactly the compilation command triggering the
above error?
The following does it for me:
clang++ --include linux/types.h ./tools/lib/bpf/bpf_helper_defs.h
Thanks. It would be good if you add the above compilation command
in the commit message.
Sure, will add.
Before:
static void *(*bpf_map_lookup_elem)(void *map, const void *key) = (void *) 1;
After:
static void *(*bpf_map_lookup_elem)(void *map, const void *key) = (void *(*)(void *map, const void *key)) 1;
Signed-off-by: Peng Wei <pengweiprc@xxxxxxxxxx>
Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
---
scripts/bpf_doc.py | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/scripts/bpf_doc.py b/scripts/bpf_doc.py
index eaae2ce78381..fa21137a90e7 100755
--- a/scripts/bpf_doc.py
+++ b/scripts/bpf_doc.py
@@ -827,6 +827,9 @@ COMMANDS
print(' *{}{}'.format(' \t' if line else '', line))
print(' */')
+ fptr_type = '%s%s(*)(' % (
+ self.map_type(proto['ret_type']),
+ ((' ' + proto['ret_star']) if proto['ret_star'] else ''))
print('static %s %s(*%s)(' % (self.map_type(proto['ret_type']),
proto['ret_star'], proto['name']), end='')
comma = ''
@@ -845,8 +848,10 @@ COMMANDS
one_arg += '{}'.format(n)
comma = ', '
print(one_arg, end='')
+ fptr_type += one_arg
- print(') = (void *) %d;' % helper.enum_val)
+ fptr_type += ')'
+ print(') = (%s) %d;' % (fptr_type, helper.enum_val))
print('')
###############################################################################
