Comments (13)
drzaeus77
commented on May 14, 2024
The pending fix addresses the buggy rewrite pass that was mangling the sample you included. However, you will still need to pass &req, since the prototype for lookup/delete/etc. is a pointer to a key, which therefore should be struct request **
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brendangregg
commented on May 14, 2024
ok, sounds good, thanks.
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brendangregg
commented on May 14, 2024
I really want to use this, but got a build error:
[...]
/mnt/src/bcc/src/cc/frontends/clang/b_frontend_action.cc: At global scope:
/mnt/src/bcc/src/cc/frontends/clang/b_frontend_action.cc:437:1: error: prototype for ‘ebpf::BFrontendAction::BFrontendAction(llvm::raw_ostream&, unsigned int)’ does not match any in class ‘ebpf::BFrontendAction’
BFrontendAction::BFrontendAction(llvm::raw_ostream &os, unsigned flags)
^
In file included from /mnt/src/bcc/src/cc/frontends/clang/b_frontend_action.cc:26:0:
/mnt/src/bcc/src/cc/frontends/clang/b_frontend_action.h:95:7: error: candidates are: ebpf::BFrontendAction::BFrontendAction(ebpf::BFrontendAction&&)
class BFrontendAction : public clang::ASTFrontendAction {
^
/mnt/src/bcc/src/cc/frontends/clang/b_frontend_action.h:95:7: error: ebpf::BFrontendAction::BFrontendAction(const ebpf::BFrontendAction&)
/mnt/src/bcc/src/cc/frontends/clang/b_frontend_action.h:99:12: error: ebpf::BFrontendAction::BFrontendAction(llvm::raw_ostream&)
explicit BFrontendAction(llvm::raw_ostream &os);
^
/mnt/src/bcc/src/cc/frontends/clang/b_frontend_action.cc: In member function ‘virtual void ebpf::BFrontendAction::EndSourceFileAction()’:
/mnt/src/bcc/src/cc/frontends/clang/b_frontend_action.cc:443:7: error: ‘flags_’ was not declared in this scope
if (flags_ & 0x4)
^
make[2]: *** [src/cc/frontends/clang/CMakeFiles/clang_frontend.dir/b_frontend_action.cc.o] Error 1
make[1]: *** [src/cc/frontends/clang/CMakeFiles/clang_frontend.dir/all] Error 2
make: *** [all] Error 2from bcc.
drzaeus77
commented on May 14, 2024
There must be some stale code hanging around somewhere. Did you try the usual suspects, like cleaning the build directory?
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brendangregg
commented on May 14, 2024
Yes, both make clean, and deleting the build directory...
# cksum src/cc/frontends/clang/b_frontend_action.cc tests/cc/test_clang.py
2865925912 18014 src/cc/frontends/clang/b_frontend_action.cc
4147208165 3547 tests/cc/test_clang.pyfrom bcc.
drzaeus77
commented on May 14, 2024
That's indeed very odd. Nothing comes to mind...let me know how I might help. The build passed on both buildbots, with gcc4.8+ubuntu14.04 and clang+fedora22 variants, as well as my arch linux gcc 5.2 box.
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brendangregg
commented on May 14, 2024
Might have been an older clang (rebuilding). I get further on a newer built system:
# ./disksnoop.py
<bcc-memory-buffer>:24:51: error: cannot take the address of an rvalue of type 'u64' (aka 'unsigned long long')
bpf_map_update_elem((void *)bpf_pseudo_fd(1, 3), &((u64)ctx->di), &ts, BPF_ANY);
^ ~~~~~~~~~~~~
<bcc-memory-buffer>:33:60: error: use of undeclared identifier 'u'
tsp = bpf_map_lookup_elem((void *)bpf_pseudo_fd(1, 3), &((u);
^
<bcc-memory-buffer>:43:2: error: expected '}'
}
^
<bcc-memory-buffer>:30:74: note: to match this '{'
int kprobe__blk_update_request(struct pt_regs *ctx, struct request *req) {
^
3 errors generated.
Traceback (most recent call last):
File "./disksnoop.py", line 19, in <module>
b = BPF(src_file="disksnoop.c")
File "/usr/lib/python2.7/dist-packages/bcc/__init__.py", line 349, in __init__
raise Exception("Failed to compile BPF module %s" % src_file)
Exception: Failed to compile BPF module disksnoop.cRunning:
#include <uapi/linux/ptrace.h>
#include <linux/blkdev.h>
BPF_HASH(start, struct request *);
int kprobe__blk_start_request(struct pt_regs *ctx, struct request *req) {
u64 ts;
// stash start timestamp by request ptr
ts = bpf_ktime_get_ns();
start.update(&req, &ts);
return 0;
}
int kprobe__blk_update_request(struct pt_regs *ctx, struct request *req) {
u64 *tsp, delta;
tsp = start.lookup(&req);
if (tsp != 0) {
delta = bpf_ktime_get_ns() - *tsp;
bpf_trace_printk("%d %x %d\n", req->__data_len,
req->cmd_flags, delta / 1000);
start.delete(&req);
}
return 0;
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drzaeus77
commented on May 14, 2024
This should have been fixed by this very commit. Have you done make install?
A new parameter with the recent changeset is BPF(..., debug=0x4) which will print the clang-rewritten source. If you see no output when providing that flag, then the old library is still being loaded.
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brendangregg
commented on May 14, 2024
debug=0x4 prints nothing new. I've done a fresh bcc build with https://raw.githubusercontent.com/iovisor/bcc/3c4a29ced84bea80b957d21256d529afb02eb634/src/cc/frontends/clang/b_frontend_action.cc ...
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drzaeus77
commented on May 14, 2024
Can you try from HEAD? There is a further fix that went in at 0ac26e8, as well the debug=0x4 flag requires a bunch of extra file changes to pass the flag to BFrontendAction.
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brendangregg
commented on May 14, 2024
I still can't see any debug code...
# clang --version
clang version 3.8.0 (http://llvm.org/git/clang.git 93885ee97cd4a65cc773a654cb2d15b2890c81a2) (http://llvm.org/git/llvm.git 2354b37ae030104dd424149804946722fce72872)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /mnt/src/llvm/build/install/binfrom bcc.
brendangregg
commented on May 14, 2024
Ok, back to the system I rebuilt clang on... that now works with disksnoop.c as listed previously. This works, thanks!
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drzaeus77
commented on May 14, 2024
Ok, closing then :)
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