jackmanb added a comment.
Sorry I was disrupted and not able to work on this last week! I've just got
started trying to integrate this with my kernel patches.
================
Comment at: llvm/lib/Target/BPF/BPFInstrInfo.td:666
+ def XADDD : XADD<BPF_DW, "u64", atomic_load_add_64>;
+ }
+}
----------------
FYI - I just spotted some stray `\t` in here (is it helpful to point this out?
If not let me know, I will ignore in future)
================
Comment at: llvm/lib/Target/BPF/BPFInstrInfo.td:684
+ let Inst{47-32} = addr{15-0}; // offset
+ let Inst{11-8} = val;
+ let Inst{7-4} = Opc.Value;
----------------
Sorry I'm a beginner with the LLVM code, could you explain what `val` does? I
didn't notice this when I looked through here before.
To try and get a clue I tried just removing this line and then compiling the
following code:
```C
// SPDX-License-Identifier: GPL-2.0
#include <stdatomic.h>
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
__u64 test_data_64 = 0;
__u64 test1_result = 0;
SEC("fentry/bpf_fentry_test1")
int BPF_PROG(test1, int a)
{
/* atomic_fetch_add(&test_data_64, 1); */
test1_result = __sync_fetch_and_add(&test_data_64, 1);
return 0;
}
```
And I was able to load and run the program, with the kernel on my WIP branch:
https://github.com/bjackman/linux-bpf/tree/wips/bpf-atomics-v0
The result looks like this:
```shell
$ llvm-objdump -d atomics_test.o
atomics_test.o: file format elf64-bpf
Disassembly of section fentry/bpf_fentry_test1:
0000000000000000 <test1>:
0: b7 01 00 00 01 00 00 00 r1 = 1
1: 18 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r2 = 0 ll
3: db 12 00 00 01 00 00 00 r1 = atomic_fetch_add((u64 *)(r2 + 0),
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash
backtrace.
Stack dump:
0. Program arguments: llvm-objdump -d atomics_test.o
Segmentation fault
```
Aside from the fact that llvm-objdump crashed, the encoding `db 12 00 00 01 00
00 00` seems correct to me. If I add the `let Inst{11-8} = val` back in I get
`db 12 00 00 01 01 00 00` which I don't understand.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D72184/new/
https://reviews.llvm.org/D72184
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
