[lldb] Cannot evaluate the value of a static local variable of an optimized-out inlined function.

[dzhidzhoev]

After #159104, if a function is optimized-out, DIEs for static local variables referenced from the function's inlined instance go to the function's abstract DIE. gdb can discover such variables, but lldb cannot, apparently.

Example source file:

➜  cat ../test-static-local.cpp
__attribute__((always_inline))
static int foo() {
    static int x = 35;
    int y = 25;
    return x;
}

int main() {
    foo();
    return foo();
}

➜  bin/clang ../test-static-local.cpp -g -o test-static-local -O0

LLDB and gdb behavior:

➜  bin/lldb test-static-local                                    
(lldb) b foo
Breakpoint 1: 2 locations.
(lldb) r
Process 38232 launched: '/home/parallels/llvm/build/native/test-static-local' (aarch64)
Process 38232 stopped
* thread #1, name = 'test-static-loc', stop reason = breakpoint 1.1
    frame #0: 0x0000aaaaaaaa06f4 test-static-local`foo() at test-static-local.cpp:4:9 [inlined]
-> 4   	    int y = 25;
(lldb) p y
(int) 4980991
(lldb) p x
         ˄
         ╰─ error: use of undeclared identifier 'x'
(lldb) q

➜  gdb test-static-local 
GNU gdb (Ubuntu 16.2-8ubuntu1) 16.2
(gdb) b foo
Breakpoint 1 at 0x6f4: foo. (2 locations)
(gdb) r
Breakpoint 1.1, foo () at ../test-static-local.cpp:4
4	    int y = 25;
(gdb) p x
$1 = 35
(gdb) p y
$2 = 5701887

Dwarfdump: https://gist.github.com/dzhidzhoev/b4ca1d74014b25642de6621fb677c35b

[llvmbot]

@llvm/issue-subscribers-lldb

Author: Vladislav Dzhidzhoev (dzhidzhoev)

After https://github.com//pull/159104, if a function is optimized-out, DIEs for static local variables referenced from the function's inlined instance go to the function's abstract DIE. gdb can discover such variables, but lldb cannot, apparently.

Example source file:

➜  cat ../test-static-local.cpp
__attribute__((always_inline))
static int foo() {
    static int x = 35;
    int y = 25;
    return x;
}

int main() {
    foo();
    return foo();
}

➜  bin/clang ../test-static-local.cpp -g -o test-static-local -O0

LLDB and gdb behavior:

➜  bin/lldb test-static-local                                    
(lldb) b foo
Breakpoint 1: 2 locations.
(lldb) r
Process 38232 launched: '/home/parallels/llvm/build/native/test-static-local' (aarch64)
Process 38232 stopped
* thread #<!-- -->1, name = 'test-static-loc', stop reason = breakpoint 1.1
    frame #<!-- -->0: 0x0000aaaaaaaa06f4 test-static-local`foo() at test-static-local.cpp:4:9 [inlined]
-&gt; 4   	    int y = 25;
(lldb) p y
(int) 4980991
(lldb) p x
         ˄
         ╰─ error: use of undeclared identifier 'x'
(lldb) q

➜  gdb test-static-local 
GNU gdb (Ubuntu 16.2-8ubuntu1) 16.2
(gdb) b foo
Breakpoint 1 at 0x6f4: foo. (2 locations)
(gdb) r
Breakpoint 1.1, foo () at ../test-static-local.cpp:4
4	    int y = 25;
(gdb) p x
$1 = 35
(gdb) p y
$2 = 5701887

Dwarfdump: https://gist.github.com/dzhidzhoev/b4ca1d74014b25642de6621fb677c35b

[Michael137]

LLDB does try to parse the DIE for x, and determines correctly that it's a static variable (at least when DIL is enabled, which on top-of-tree it is by default). But the SymbolContext::function isn't populated when we get to SymbolFileDWARF::ParseVariableDIE, so we bail:

llvm-project/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

Lines 3807 to 3812 in 862a1be

	if (!symbol_context_scope) {
	// Not ready to parse this variable yet. It might be a global or static
	// variable that is in a function scope and the function in the symbol
	// context wasn't filled in yet
	return nullptr;
	}

[dzhidzhoev]

#159104 was reverted, but the issue can be reproduced with gcc with the same test source code file.