Fedora Linux fails `Unwind/thread-step-out-ret-addr-check.test`

[jankratochvil]

Summary

D71372 introduced: Unwind/thread-step-out-ret-addr-check.test failing on Fedora 30 Linux x86_64.

One problem is the underscored _nonstandard_stub in the .s file but not in the LLDB command:

(lldb) breakpoint set -n nonstandard_stub
Breakpoint 1: no locations (pending).
WARNING:  Unable to resolve breakpoint to any actual locations.
(lldb) process launch
Process 21919 exited with status = 0 (0x00000000)
Process 21919 launched: '/home/jkratoch/redhat/llvm-monorepo-clangassert/tools/lldb/test/Unwind/Output/thread-step-out-ret-addr-check.test.tmp' (x86_64)
(lldb) thread step-out
error: invalid thread
(lldb) _

Another problem is that Fedora Linux has executable stack by default and all programs indicate non-executable stack by PT_GNU_STACK, after fixing the underscore I was getting:

(lldb) thread step-out
Process 22294 exited with status = 0 (0x00000000)
(lldb) _

Is the .section harmless for non-Linux platforms or will it need some conditional compilation? (#ifdef is not available in .s file)

[mossberg]

Thanks for looking into this @jankratochvil!

Another problem is that Fedora Linux has executable stack by default and all programs indicate non-executable stack by PT_GNU_STACK, after fixing the underscore I was getting:

(lldb) thread step-out
Process 22294 exited with status = 0 (0x00000000)
(lldb) _
Is the .section harmless for non-Linux platforms or will it need some conditional compilation? (#ifdef is not available in .s file)

Ok, I guess I was incorrectly assuming the stack should be non-executable by default on all platforms. In this case, let's rewrite the test to have a variable that is actually in the .data section (therefore guaranteed to be non-executable), and pass a pass a pointer to it to nonstandard_stub. The core requirement is that the pointer passed to nonstandard_stub must simply point to some kind of non-executable memory. I can do this.

lldb/test/Shell/Unwind/Inputs/thread-step-out-ret-addr-check.s

13

Maybe we can just remove the underscore version, and simply use nonstandard_stub if it will work everywhere?

[mossberg]

The Windows failure (https://reviews.llvm.org/D71372#1793371) seems like it may also be caused by the underscore symbol issue.

[labath]

As I said on the other patch, this is probably a simpler approach (assuming we can't find a way to make the data section non-executable in a generic way). You'll need to add an #ifdef for the section directive though...

lldb/test/Shell/Unwind/Inputs/thread-step-out-ret-addr-check.s

13

Yes, I'm pretty sure that would work.

[jankratochvil]

Addressed the review and D71789 and enabled it for Linux again.

[jankratochvil]

Thanks for the review but is it tested on Darwin? I do not have any.

[labath]

I didn't check this patch exactly, but I tried something very similar investigating this patch yesterday, so I think this should be fine. You should be able to see any darwin failures here: http://lab.llvm.org:8080/green/view/LLDB/job/lldb-cmake/

lldb/test/Shell/Unwind/Inputs/thread-step-out-ret-addr-check.s

         .text
         .globl  asm_main
 asm_main:
         sub $0x8, %rsp
         movq $0, (%rsp)
         push %rsp
-        jmp _nonstandard_stub
+        jmp nonstandard_stub
 
 # Takes a single pointer argument via the stack, which is nonstandard for x64.
 # Executing 'thread step-out' here will initially attempt to write a
 # breakpoint to that stack address, but should fail because of the executable
 # memory check.
-_nonstandard_stub:
+nonstandard_stub:
         mov (%rsp), %rdi
         mov (%rdi), %rsi
         add $1, %rsi
         mov %rsi, (%rdi)
 
         add $0x10, %rsp
         ret
+
+#ifdef __linux__
+        .section .note.GNU-stack,"",@progbits
+#endif

lldb/test/Shell/Unwind/thread-step-out-ret-addr-check.test

 # Test that `thread step-out` fails when the "return address"
 # points to non-executable memory.
 
-# REQUIRES: target-x86_64, system-darwin
+# REQUIRES: target-x86_64
 
 # RUN: %clang_host %p/Inputs/call-asm.c %p/Inputs/thread-step-out-ret-addr-check.s -o %t
 # RUN: %lldb %t -s %s -b 2>&1 | FileCheck %s
 
 breakpoint set -n nonstandard_stub
 # CHECK: Breakpoint 1: where = {{.*}}`nonstandard_stub
 
 process launch
 # CHECK: stop reason = breakpoint 1.1
 
 thread step-out
 # CHECK: Could not create return address breakpoint.
 # CHECK: Return address (0x{{[a-f0-9]*}}) did not point to executable memory.