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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
6 lines
220 B
C
6 lines
220 B
C
// RUN: %clang_cc1 -triple bpf-pc-linux-gnu -ast-dump %s \
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// RUN: | FileCheck --strict-whitespace %s
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int __attribute__((btf_type_tag("rcu"))) * g;
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// CHECK: VarDecl{{.*}}g 'int __attribute__((btf_type_tag("rcu")))*'
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