[PATCH] D97986: BPF: permit type modifiers for __builtin_btf_type_id() relocation

[Yonghong Song via Phabricator via llvm-commits]

yonghong-song added inline comments.


================
Comment at: llvm/lib/Target/BPF/BPFPreserveDIType.cpp:91
+        if (Tag != dwarf::DW_TAG_const_type &&
+            Tag != dwarf::DW_TAG_volatile_type)
+          break;
----------------
anakryiko wrote:
> should we strip `restrict` as well?
I deliberately skipped the `restrict`. in C, `restrict` is used to restrict pointers and used in pointer declarations (include variables and parameters). 
  https://en.wikipedia.org/wiki/Restrict
In type casting, the `restrict` will be ignored. For example, 
```
-bash-4.4$ cat tt.c
struct s {
  int a;
};
int test() {
  return __builtin_btf_type_id(*(struct s * restrict)0, 1);
}
-bash-4.4$ clang -target bpf -O2 -S -g tt.c -emit-llvm -Xclang -disable-llvm-passes
```
restrict does not show up in the debuginfo.

I tried to construct another example,
```
-bash-4.4$ cat tt.c                                                               
struct s {
  int a;
};

int test() {
  struct s * restrict v;
  return __builtin_btf_type_id(*v, 1);
}
```
In this case, "restrict" shows up in variable declaration as restrict -> pointer -> struct s.
The meta data we attached is the pointee type "struct s", so we are fine.

typically `restrict` shows up before pointer like [restrict|const|volatile]+ pointer [const|volatile]+ non-pointer type.

What I did is trying to remove const/volatile in "[const|volatile]+ non-pointer-type". So we should be fine here.




Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D97986/new/

https://reviews.llvm.org/D97986