https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90279
Bug ID: 90279
Summary: DW_AT_location missing for struct-based Variable
Product: gcc
Version: 8.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: daniel.penning at embeff dot com
Target Milestone: ---
------------------------------------------------
struct StrongType {
explicit StrongType(int val) : m_value(val) { }
int m_value;
};
StrongType Square(StrongType val) {
return StrongType{val.m_value * val.m_value};
}
int EvalDwarfStrong(int var) {
StrongType strongArg{var};
StrongType strongRes = Square(strongArg);
return strongRes.m_value;
}
------------------------------------------------
gcc -Og -g
dwarfdump outputs the following information for the strongArg variable:
< 2><0x000000a6> DW_TAG_variable
DW_AT_name strongArg
DW_AT_decl_file 0x00000001
<SystemSpecific>/DwarfStrong.cpp
DW_AT_decl_line 0x0000000b
DW_AT_type <0x0000002d>
There is no DW_AT_location specified, so a debugger will not be able to display
its value.
This is not a problem-per-se with the struct since the DWARF output for the
Square() function argument is using a correct DW_AT_location.
The compiler is not inlining the function call with -Og so the variable will be
available right before the function call to Square().
Using the same code, but with a plain int instead of the struct-wrapper yields
the desired output:
-----------------------------------------------------
int Square(int val) {
return val*val;
}
int EvalDwarfUnsafe(int var) {
int unsafeArg{var};
int unsafeRes = Square(unsafeArg);
return unsafeRes;
}
< 2><0x00000061> DW_TAG_variable
DW_AT_name unsafeArg
DW_AT_decl_file
0x00000001<SystemSpecific>/DwarfUnsafe.cpp
DW_AT_decl_line 0x00000006
DW_AT_type <0x00000093>
DW_AT_location <loclist at offset
0x00000039 with 2 entries follows>
[ 0]< offset pair low-off : 0x00000006 addr 0x00000006
high-off 0x0000000a addr 0x0000000a>DW_OP_reg5
[ 1]< offset pair low-off : 0x0000000a addr 0x0000000a
high-off 0x0000000d addr 0x0000000d>DW_OP_GNU_entry_value 0x00000001 contents
0x55 DW_OP_stack_value
