You signed in with another tab or window. Reload to refresh your session.You signed out in another tab or window. Reload to refresh your session.You switched accounts on another tab or window. Reload to refresh your session.Dismiss alert
In the reproducer below, the variable 'local' has no location around the call to 'ext' when built with "-O2 -g -c" (targeting x86_64-unknown-linux-gnu):
It looks like the DBG_VALUE describing the stack home uses a frame index location which is rewritten in terms of RSP by Prologue/Epilogue Insertion (prologepilog). DbgEntityHistoryCalculator then terminates the location range at the first stack adjustment because RSP is clobbered.
This has been discussed on llvm-dev with the subject line "[llvm-dev] [debug-info] Stack pointer based variable locations". The preferred solution currently appears to be to set DW_AT_frame_base to DW_OP_call_frame_cfa in the parent subroutine DIE and use DW_OP_fbreg to describe the stack location.
Extended Description
In the reproducer below, the variable 'local' has no location around the call to 'ext' when built with "-O2 -g -c" (targeting x86_64-unknown-linux-gnu):
clang built at 71597d4.
$ cat test.cpp
void ext(int, int, int, int, int, int, int, int, int, int);
void escape(int*);
int example() {
int local = 0;
escape(&local);
ext(0, 1, 2, 3, 4, 5, 6, 7, 8, 9);
local += 2;
return local;
}
$ clang -O2 -g -c test.cpp -o test.o
$ llvm-objdump -d test.o
test.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <_Z7examplev>:
0: 50 pushq %rax
1: c7 44 24 04 00 00 00 00 movl $0, 4(%rsp)
9: 48 8d 7c 24 04 leaq 4(%rsp), %rdi
e: e8 00 00 00 00 callq 0x13 <_Z7examplev+0x13>
13: 31 ff xorl %edi, %edi
15: be 01 00 00 00 movl $1, %esi
1a: ba 02 00 00 00 movl $2, %edx
1f: b9 03 00 00 00 movl $3, %ecx
24: 41 b8 04 00 00 00 movl $4, %r8d
2a: 41 b9 05 00 00 00 movl $5, %r9d
30: 6a 09 pushq $9
32: 6a 08 pushq $8
34: 6a 07 pushq $7
36: 6a 06 pushq $6
38: e8 00 00 00 00 callq 0x3d <_Z7examplev+0x3d>
3d: 48 83 c4 20 addq $32, %rsp
41: 8b 44 24 04 movl 4(%rsp), %eax
45: 83 c0 02 addl $2, %eax
48: 59 popq %rcx
49: c3 retq
$ llvm-dwarfdump test.o --name local
test.o: file format elf64-x86-64
0x00000047: DW_TAG_variable
DW_AT_location (0x00000000:
[0x0000000000000001, 0x0000000000000009): DW_OP_consts +0, DW_OP_stack_value
[0x0000000000000009, 0x0000000000000032): DW_OP_breg7 RSP+4
[0x0000000000000045, 0x000000000000004a): DW_OP_reg0 RAX)
DW_AT_name ("local")
DW_AT_decl_file ("test.cpp")
DW_AT_decl_line (4)
The variable 'local' is not given a location over the interval [32, 45) even though its stack home is still valid here (RSP+8, RSP+12, ...).
The text was updated successfully, but these errors were encountered: