On 2015/7/30 1:13, Alexei Starovoitov wrote:
[SNIP]
probably both A and B won't really work when programs get bigger
and optimizations will start moving lines around.
the builtin_dwarf_type idea is actually quite interesting.
Potentially that builtin can stringify type name and later we can
search it in dwarf. Please take a look how to add such builtin.
There are few similar builtins that deal with exception handling
and need type info. May be they can be reused. Like:
int_eh_typeid_for and int_eh_dwarf_cfa
Hi Alexei,
I have tested int_eh_dwarf_cfa and int_eh_typeid_for.
By implementing ISD::FRAMEADDR support in LLVM BPF backend users are
allowed to
fetch frame address R11. __builtin_frame_addr(0) and __builtin_dwarf_cfa()
will be enabled.
By emitting llvm.eh_typeid_for in clang we can utilize it go generate an
unique
ID from a pointer of user defined type. However, we can't use pointer of
local
variables.
I attach a sample program and the resuling asm output at the bottom of
this mail.
Looks like llvm.eh_typeid_for meets our goal further. However, currently
it is
still ugly:
1. llvm.eh_typeid_for can be used on global variables only. So for each
output
structure we have to define a global varable.
2. We still need to find a way to connect the fetchd typeid with DWARF info.
Inserting that ID into DWARF may workable?
However with the newest llvm + clang the DWARF info is still incorrect:
$ objdump --dwarf=info ./out.o
...
<1><3f>: Abbrev Number: 3 (DW_TAG_structure_type)
<40> DW_AT_name : (indirect string, offset: 0x0): clang
version 3.8.0 (http://llvm.org/git/clang.git
f0fcd3432cbed83500df70c18f275d8affb89e5e) (http://llvm.org/git/llvm.git
c8ccd78d31d4949fa1c14e954ccb06253e18cf37)
<44> DW_AT_byte_size : 8
<45> DW_AT_decl_file : 1
<46> DW_AT_decl_line : 4
<2><47>: Abbrev Number: 4 (DW_TAG_member)
<48> DW_AT_name : (indirect string, offset: 0x0): clang
version 3.8.0 (http://llvm.org/git/clang.git
f0fcd3432cbed83500df70c18f275d8affb89e5e) (http://llvm.org/git/llvm.git
c8ccd78d31d4949fa1c14e954ccb06253e18cf37)
<4c> DW_AT_type : <0x60>
<50> DW_AT_decl_file : 1
<51> DW_AT_decl_line : 5
<52> DW_AT_data_member_location: 0
<2><53>: Abbrev Number: 4 (DW_TAG_member)
<54> DW_AT_name : (indirect string, offset: 0x0): clang
version 3.8.0 (http://llvm.org/git/clang.git
f0fcd3432cbed83500df70c18f275d8affb89e5e) (http://llvm.org/git/llvm.git
c8ccd78d31d4949fa1c14e954ccb06253e18cf37)
<58> DW_AT_type : <0x60>
<5c> DW_AT_decl_file : 1
<5d> DW_AT_decl_line : 6
<5e> DW_AT_data_member_location: 4
...
The DW_AT_name is missing.
I'll post 2 LLVM patches by replying this mail. Please have a look and
help me
send them to LLVM if you think my code is correct.
Following is the sample code and resuling ASM:
========================================================
static int (*test_func)(unsigned long) = (void *) 0x1234;
struct my_str {
int x;
int y;
};
struct my_str __str_my_str;
struct my_str2 {
int x;
int y;
int z;
};
struct my_str2 __str_my_str2;
int func(int *ctx)
{
struct my_str var_a;
struct my_str2 var_b;
test_func((void*)&var_a - __builtin_dwarf_cfa());
test_func(__builtin_bpf_typeid(&__str_my_str));
test_func(__builtin_bpf_typeid(&__str_my_str2));
return 0;
}
==================== the resuling asm code =============
.text
.globl func
.align 8
func: # @func
# BB#0: # %entry
mov r1, r10
addi r1, -8
sub r1, r11
call 4660
mov r1, 1
call 4660
mov r1, 2
call 4660
mov r0, 0
ret
.comm __str_my_str,8,4 # @__str_my_str
.comm __str_my_str2,12,4 # @__str_my_str2
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