llvm-project/clang/test/AST/ast-dump-bpf-attr.c

// RUN: %clang_cc1 -triple bpf-pc-linux-gnu -ast-dump  %s \
// RUN: | FileCheck --strict-whitespace %s

int __attribute__((btf_type_tag("rcu"))) * g;
// CHECK: VarDecl{{.*}}g 'int  __attribute__((btf_type_tag("rcu")))*'
[Clang][BPF] Type print btf_type_tag properly When running bcc tool execsnoop ([1]) which is built with latest llvm, I hit the following error: $ sudo ./execsnoop.py /virtual/main.c:99:157: error: expected ')' data.ppid = ({ typeof(pid_t) _val; __builtin_memset(&_val, 0, sizeof(_val)); bpf_probe_read(&_val, sizeof(_val), (void )&({ typeof(struct task_struct btf_type_tag(rcu)) _val; __builtin_memset(&_val, 0, sizeof(_val)); ^ bpf_probe_read(&_val, sizeof(_val), (void )&task->real_parent); _val; })->tgid); _val; }); The failure reason is due to that the bcc rewriter printed type like struct task_struct btf_type_tag(rcu) where the compiler cannot recognize what 'btf_type_tag(rcu)' is. The above type is printed in [2] by UnaryOperator->getType().getAsString() (from clang) in function ProbeVisitor::VisitUnaryOperator. The original source type looks like ([3]) struct task_struct { ... struct task_struct __rcu real_parent; ... } where '__rcu' is a macro expanding to '__attribute__((btf_type_tag("rcu")))'. Let us print btf_type_tag properly in clang so bcc tools and broader type printing will work properly. With this patch, the above rewrited source code looks like data.ppid = ({ typeof(pid_t) _val; __builtin_memset(&_val, 0, sizeof(_val)); bpf_probe_read(&_val, sizeof(_val), (void )&({ typeof(struct task_struct __attribute__((btf_type_tag("rcu")))) _val; __builtin_memset(&_val, 0, sizeof(_val)); bpf_probe_read(&_val, sizeof(_val), (void )&task->real_parent); _val; })->tgid); _val; }); and execsnoop.py tool can run properly. [1] https://github.com/iovisor/bcc/blob/master/tools/exitsnoop.py [2] https://github.com/iovisor/bcc/blob/master/src/cc/frontends/clang/b_frontend_action.cc [3] https://github.com/torvalds/linux/blob/master/include/linux/sched.h Differential Revision: https://reviews.llvm.org/D150017 2023-05-05 14:41:13 -07:00			`// RUN: %clang_cc1 -triple bpf-pc-linux-gnu -ast-dump %s \`
			`// RUN: \| FileCheck --strict-whitespace %s`

			`int __attribute__((btf_type_tag("rcu"))) * g;`
			`// CHECK: VarDecl{{.}}g 'int __attribute__((btf_type_tag("rcu")))'`