forked from OSchip/llvm-project
e3d8ebe158
With link-time optimizations enabled, resulting DWARF mayend up containing
cross CU references (through the DW_AT_abstract_origin attribute).
Consider the following example:
// sum.c
__attribute__((always_inline)) int sum(int a, int b)
{
return a + b;
}
// main.c
extern int sum(int, int);
int main()
{
int a = 5, b = 10, c = sum(a, b);
return 0;
}
Compiled as follows:
$ clang -g -flto -fuse-ld=lld main.c sum.c -o main
Results in the following DWARF:
-- sum.c CU: abstract instance tree
...
0x000000b0: DW_TAG_subprogram
DW_AT_name ("sum")
DW_AT_decl_file ("sum.c")
DW_AT_decl_line (1)
DW_AT_prototyped (true)
DW_AT_type (0x000000d3 "int")
DW_AT_external (true)
DW_AT_inline (DW_INL_inlined)
0x000000bc: DW_TAG_formal_parameter
DW_AT_name ("a")
DW_AT_decl_file ("sum.c")
DW_AT_decl_line (1)
DW_AT_type (0x000000d3 "int")
0x000000c7: DW_TAG_formal_parameter
DW_AT_name ("b")
DW_AT_decl_file ("sum.c")
DW_AT_decl_line (1)
DW_AT_type (0x000000d3 "int")
...
-- main.c CU: concrete inlined instance tree
...
0x0000006d: DW_TAG_inlined_subroutine
DW_AT_abstract_origin (0x00000000000000b0 "sum")
DW_AT_low_pc (0x00000000002016ef)
DW_AT_high_pc (0x00000000002016f1)
DW_AT_call_file ("main.c")
DW_AT_call_line (5)
DW_AT_call_column (0x19)
0x00000081: DW_TAG_formal_parameter
DW_AT_location (DW_OP_reg0 RAX)
DW_AT_abstract_origin (0x00000000000000bc "a")
0x00000088: DW_TAG_formal_parameter
DW_AT_location (DW_OP_reg2 RCX)
DW_AT_abstract_origin (0x00000000000000c7 "b")
...
Note that each entry within the concrete inlined instance tree in
the main.c CU has a DW_AT_abstract_origin attribute which
refers to a corresponding entry within the abstract instance
tree in the sum.c CU.
llvm-dwarfdump --statistics did not properly report
DW_TAG_formal_parameters/DW_TAG_variables from concrete inlined
instance trees which had 0% location coverage and which
referred to a different CU, mainly because information about abstract
instance trees and their parameters/variables was stored
locally - just for the currently processed CU,
rather than globally - for all CUs.
In particular, if the concrete inlined instance tree from
the example above was to look like this
(i.e. parameter b has 0% location coverage, hence why it's missing):
0x0000006d: DW_TAG_inlined_subroutine
DW_AT_abstract_origin (0x00000000000000b0 "sum")
DW_AT_low_pc (0x00000000002016ef)
DW_AT_high_pc (0x00000000002016f1)
DW_AT_call_file ("main.c")
DW_AT_call_line (5)
DW_AT_call_column (0x19)
0x00000081: DW_TAG_formal_parameter
DW_AT_location (DW_OP_reg0 RAX)
DW_AT_abstract_origin (0x00000000000000bc "a")
llvm-dwarfdump --statistics would have not reported b as such.
Patch by Dimitrije Milosevic.
Differential revision: https://reviews.llvm.org/D113465
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|---|---|---|
| .. | ||
| fuzzer | ||
| CMakeLists.txt | ||
| SectionSizes.cpp | ||
| Statistics.cpp | ||
| llvm-dwarfdump.cpp | ||
| llvm-dwarfdump.h | ||