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Subject[PATCH v2] bpf/scripts: Generate GCC compatible helpers
Date
The current bpf_helper_defs.h helpers are llvm specific and don't work
correctly with gcc.

GCC appears to required kernel helper funcs to have the following
attribute set: __attribute__((kernel_helper(NUM)))

Generate gcc compatible headers based on the format in bpf-helpers.h.

This adds conditional blocks for GCC while leaving clang codepaths
unchanged, for example:
#if __GNUC__ && !__clang__
void *bpf_map_lookup_elem(void *map, const void *key) __attribute__((kernel_helper(1)));
#else
static void *(*bpf_map_lookup_elem)(void *map, const void *key) = (void *) 1;
#endif

#if __GNUC__ && !__clang__
long bpf_map_update_elem(void *map, const void *key, const void *value, __u64 flags) __attribute__((kernel_helper(2)));
#else
static long (*bpf_map_update_elem)(void *map, const void *key, const void *value, __u64 flags) = (void *) 2;
#endif

See:
https://github.com/gcc-mirror/gcc/blob/releases/gcc-12.1.0/gcc/config/bpf/bpf-helpers.h#L24-L27

This fixes the following build error:
error: indirect call in function, which are not supported by eBPF

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
Changes v1 -> v2:
- more details in commit log
---
scripts/bpf_doc.py | 43 ++++++++++++++++++++++++++-----------------
1 file changed, 26 insertions(+), 17 deletions(-)

diff --git a/scripts/bpf_doc.py b/scripts/bpf_doc.py
index a0ec321469bd..36fb400a5731 100755
--- a/scripts/bpf_doc.py
+++ b/scripts/bpf_doc.py
@@ -739,6 +739,24 @@ class PrinterHelpers(Printer):

seen_helpers = set()

+ def print_args(self, proto):
+ comma = ''
+ for i, a in enumerate(proto['args']):
+ t = a['type']
+ n = a['name']
+ if proto['name'] in self.overloaded_helpers and i == 0:
+ t = 'void'
+ n = 'ctx'
+ one_arg = '{}{}'.format(comma, self.map_type(t))
+ if n:
+ if a['star']:
+ one_arg += ' {}'.format(a['star'])
+ else:
+ one_arg += ' '
+ one_arg += '{}'.format(n)
+ comma = ', '
+ print(one_arg, end='')
+
def print_one(self, helper):
proto = helper.proto_break_down()

@@ -762,26 +780,17 @@ class PrinterHelpers(Printer):
print(' *{}{}'.format(' \t' if line else '', line))

print(' */')
+ print('#if __GNUC__ && !__clang__')
+ print('%s %s%s(' % (self.map_type(proto['ret_type']),
+ proto['ret_star'], proto['name']), end='')
+ self.print_args(proto)
+ print(') __attribute__((kernel_helper(%d)));' % len(self.seen_helpers))
+ print('#else')
print('static %s %s(*%s)(' % (self.map_type(proto['ret_type']),
proto['ret_star'], proto['name']), end='')
- comma = ''
- for i, a in enumerate(proto['args']):
- t = a['type']
- n = a['name']
- if proto['name'] in self.overloaded_helpers and i == 0:
- t = 'void'
- n = 'ctx'
- one_arg = '{}{}'.format(comma, self.map_type(t))
- if n:
- if a['star']:
- one_arg += ' {}'.format(a['star'])
- else:
- one_arg += ' '
- one_arg += '{}'.format(n)
- comma = ', '
- print(one_arg, end='')
-
+ self.print_args(proto)
print(') = (void *) %d;' % len(self.seen_helpers))
+ print('#endif')
print('')

###############################################################################
--
2.34.1
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