https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109068
Bug ID: 109068
Summary: bpf: "error: too many function arguments for eBPF" for
always_inline function
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: david.faust at oracle dot com
CC: cupertino.miranda at oracle dot com, jemarch at gcc dot
gnu.org
Target Milestone: ---
Target: bpf
BPF calling convention does not support function calls with more than
5 arguments. But if the function is inlined this restriction should be
relaxed.
Many convenience macros for BPF in the kernel make use of always_inline
functions, and the expansion of the macro uses can result in an
always_inline function with >5 args. There are several examples of this
in the BPF selftests, so GCC fails to compile those tests.
e.g. on bpf-next:
linux/tools/testing/selftests/bpf/progs/bpf_syscall_macro.c
and corresponding BPF_KSYSCALL macro def in
linux/tools/testing/selftests/bpf/tools/include/bpf/bpf_tracing.h
duplicated from
linux/tools/lib/bpf/bpf_tracing.h
clang compiles these tests without issue.
We should fix the BPF backend check for function arguments to allow
calls to inline functions with >5 args.
$ cat args.c
inline __attribute__((always_inline))
int foo (int a, int b, int c, int d, int e, int f)
{
return a + b + c + d + e + f;
}
int bar (int x)
{
return foo (x, x*2, x*3, x*4, x*5, x*6);
}
$ bpf-unknown-none-gcc -c args.c -o args.o
args.c: In function ‘foo’:
args.c:2:5: error: too many function arguments for eBPF
2 | int foo (int a, int b, int c, int d, int e, int f)
| ^~~
