yonghong-song created this revision.
yonghong-song added reviewers: arsenm, aprantl, Anastasia, ast.
yonghong-song added a project: debug-info.
Herald added subscribers: cfe-commits, wdng.
Herald added a project: clang.
The RFC intends to kick off the discussion on how to support
user defined address_space attributes in dwarf.
The use case:
=============
In linux kernel, under certain make flags, pointers may be
annotated with additional address_space information. The source
code is below:
https://github.com/torvalds/linux/blob/master/include/linux/compiler_types.h
For example, we have
1. define __user __attribute__((noderef, address_space(1)))
2. define __kernel __attribute__((address_space(0)))
3. define __iomem __attribute__((noderef, address_space(2)))
4. define __percpu __attribute__((noderef, address_space(3)))
5. define __rcu __attribute__((noderef, address_space(4)))
Currently, the address_space annotation is not used when compiling
a normal (production) kernel. It is typically used during development
and used by 'sparse' tool to check proper pointer usage.
Now there is a growing need to put address_space info into debug info,
e.g., dwarf, in linux binary to help automatically differentiate
pointers accessing kernel and user memories in order to avoid
explicit user annotations like below:
http://lkml.iu.edu/hypermail/linux/kernel/1905.1/05750.html
Other tracing tools like bpftrace, bcc would have similar issues.
The current patch
=================
The proposal here is for user specified address_space, just add it
to DebugInfo and then later it will be automatically inserted into
dwarf. For example,
-bash-4.4$ cat t.c
#define __user __attribute__((noderef, address_space(3)))
void __user *g;
extern int __user *foo(int *a, int __user *b);
int __user *foo(int *a, int __user *b) { return b; }
-bash-4.4$ clang -O2 -g -c t.c
-bash-4.4$ llvm-dwarfdump t.o
...
0x0000002a: DW_TAG_variable
DW_AT_name ("g")
DW_AT_type (0x00000042 "*")
0x00000042: DW_TAG_pointer_type
DW_AT_address_class (0x00000003)
0x00000060: DW_TAG_formal_parameter
DW_AT_name ("a")
DW_AT_type (0x00000091 "int*")
0x00000071: DW_TAG_formal_parameter
DW_AT_name ("b")
DW_AT_type (0x00000081 "int*")
0x00000081: DW_TAG_pointer_type
DW_AT_type (0x0000008a "int")
DW_AT_address_class (0x00000003)
0x00000091: DW_TAG_pointer_type
DW_AT_type (0x0000008a "int")
DW_AT_address_class (0x00000000)
This patch mixed language address space and user defined address space
in the same debuginfo address_space and in the dwarf final encoding,
it is encoded as address_class which is more tailored into
language address_space.
Question:
=========
This patch probably won't work as it mixed language address_space
and user address_space.
How we should proceed from here? Separate field in
IR DebugInfo and Dwarf for user defined address_space?
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D69393
Files:
clang/lib/Basic/Targets/BPF.h
clang/lib/Basic/Targets/X86.h
Index: clang/lib/Basic/Targets/X86.h
===================================================================
--- clang/lib/Basic/Targets/X86.h
+++ clang/lib/Basic/Targets/X86.h
@@ -257,6 +257,11 @@
setFeatureEnabledImpl(Features, Name, Enabled);
}
+ Optional<unsigned>
+ getDWARFAddressSpace(unsigned AddressSpace) const override {
+ return AddressSpace;
+ }
+
// This exists purely to cut down on the number of virtual calls in
// initFeatureMap which calls this repeatedly.
static void setFeatureEnabledImpl(llvm::StringMap<bool> &Features,
Index: clang/lib/Basic/Targets/BPF.h
===================================================================
--- clang/lib/Basic/Targets/BPF.h
+++ clang/lib/Basic/Targets/BPF.h
@@ -58,6 +58,11 @@
ArrayRef<Builtin::Info> getTargetBuiltins() const override;
+ Optional<unsigned>
+ getDWARFAddressSpace(unsigned AddressSpace) const override {
+ return AddressSpace;
+ }
+
const char *getClobbers() const override { return ""; }
BuiltinVaListKind getBuiltinVaListKind() const override {
Index: clang/lib/Basic/Targets/X86.h
===================================================================
--- clang/lib/Basic/Targets/X86.h
+++ clang/lib/Basic/Targets/X86.h
@@ -257,6 +257,11 @@
setFeatureEnabledImpl(Features, Name, Enabled);
}
+ Optional<unsigned>
+ getDWARFAddressSpace(unsigned AddressSpace) const override {
+ return AddressSpace;
+ }
+
// This exists purely to cut down on the number of virtual calls in
// initFeatureMap which calls this repeatedly.
static void setFeatureEnabledImpl(llvm::StringMap<bool> &Features,
Index: clang/lib/Basic/Targets/BPF.h
===================================================================
--- clang/lib/Basic/Targets/BPF.h
+++ clang/lib/Basic/Targets/BPF.h
@@ -58,6 +58,11 @@
ArrayRef<Builtin::Info> getTargetBuiltins() const override;
+ Optional<unsigned>
+ getDWARFAddressSpace(unsigned AddressSpace) const override {
+ return AddressSpace;
+ }
+
const char *getClobbers() const override { return ""; }
BuiltinVaListKind getBuiltinVaListKind() const override {
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
