https://llvm.org/bugs/show_bug.cgi?id=24117
Bug ID: 24117
Summary: ARM64 debug info empty prologue
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: DebugInfo
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
I'm seeing a regression in generated debug line information for ARM64 with -O1,
on Darwin. Consider this simple C source:
$ cat ditest.c
#include <stdlib.h>
int main() {
char *x = (char*)malloc(10 * sizeof(char));
return x[5];
}
If I compile this with LLVM 3.6.0, and then ask `atos` to retrieve the source
line for the `malloc` call instruction, it correctly says that it's line 3:
$ ~/llvm-3.6.0/bin/clang ditest.c -o ditest -arch arm64 -g -O1
$ otool -tv ditest
ditest:
(__TEXT,__text) section
_main:
0000000100007f6c stp x29, x30, [sp, #-16]!
0000000100007f70 mov x29, sp
0000000100007f74 movz w0, #0xa
0000000100007f78 bl 0x100007f88 ; symbol stub for: _malloc
0000000100007f7c ldrsb w0, [x0, #5]
0000000100007f80 ldp x29, x30, [sp], #16
0000000100007f84 ret
$ atos -o ditest 0000000100007f78
main (in ditest) (ditest.c:3)
However, if I do the same with current LLVM trunk, `atos` says the same
instruction has source line number 2:
$ ~/llvm-trunk/bin/clang ditest.c -o ditest -arch arm64 -g -O1
$ otool -tv ditest
ditest:
(__TEXT,__text) section
_main:
0000000100007f6c stp x29, x30, [sp, #-16]!
0000000100007f70 mov x29, sp
0000000100007f74 movz w0, #0xa
0000000100007f78 bl 0x100007f88 ; symbol stub for: _malloc
0000000100007f7c ldrsb w0, [x0, #5]
0000000100007f80 ldp x29, x30, [sp], #16
0000000100007f84 ret
$ atos -o ditest 0000000100007f78
main (in ditest) (ditest.c:2)
The difference in the DWARF line info is in the way how the end of prologue is
marked, current LLVM trunk emits:
$ dwarfdump --debug-line ditest.dSYM/Contents/Resources/DWARF/ditest
...
0x0000002b: DW_LNE_set_address( 0x0000000100007f6c )
0x00000036: address += 0, line += 1
0x0000000100007f6c 1 2 0 is_stmt
0x00000037: DW_LNS_set_column( 20 )
0x00000039: DW_LNS_set_prologue_end
0x0000003a: address += 0, line += 1
0x0000000100007f6c 1 3 20 is_stmt prologue_end
Where it looks like the `address += 0` indicates that the prologue of the
function is empty, which isn't true. The generated line information then
contains a duplicate definition for address `0x0000000100007f6c`, I don't know
if that's valid or not.
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