Re: Debugging on Linux with non-fragile ABI?

[Frederik Seiffert]

Hi Wolfgang,

We’re running into very similar issues debugging using lldb with the GNUstep 
Android toolchain, which is using the modern (v2) ABI. Have you been able to 
get any further with this?

The following lldb command seems to indicate that the root cause might be lldb 
missing knowledge about the ObjC runtime. Could you check if you get the same 
output for this?

> (lldb) language objc class-table dump
> error: current process has no Objective-C runtime loaded

Thanks,
Frederik


> Am 18.06.2019 um 02:49 schrieb Wolfgang Lux <address@hidden>:
> 
> Hi all,
> 
> has anybody tips for how to debug GNUstep executables built with the 
> non-fragile ABI?
> Gdb seems pretty useless with the non-fragile ABI because all instance 
> variable 
> offsets appear to be 0 so it's impossible to inspect the contents of any 
> instances:
> (gdb) print *self
> $1 = {<> = {isa = 0x6074f8 <_OBJC_CLASS_Test>}, 
>   name = 0x6074f8 <_OBJC_CLASS_Test>, value = 0x6074f8 <_OBJC_CLASS_Test>, 
>   parent = 0x6074f8 <_OBJC_CLASS_Test>, children = 0x6074f8 
> <_OBJC_CLASS_Test>}
> 
> I've also tried lldb, which at least understands the object layout:
> (lldb) print *self
> (Test) $0 = {
>   NSObject = {
>     isa = 0x00000000006074f8
>   }
>   name = 0x0000000000607588
>   value = 0x0000000000607588
>   parent = nil
>   children = 0x00000000007949b8
> }
> However, when I try to inspect any of the instance attributes I only get an 
> error message:
> Error [IRForTarget]: Couldn't find Objective-C indirect ivar symbol 
> OBJC_IVAR_$_Test.name
> error: The expression could not be prepared to run in the target
> (lldb) print self->value
> Error [IRForTarget]: Couldn't find Objective-C indirect ivar symbol 
> OBJC_IVAR_$_Test.value
> error: The expression could not be prepared to run in the target
> 
> I've checked this on Ubuntu 18.04 with lldb 6.0 (and before any FreeBSD 
> advocates run in, it's exactly the same on FreeBSD 11.3 which comes with lldb 
> 8.0)
> 
> All of this works fine on macOS:
> (lldb) print *self
> (Test) $0 = {
>   NSObject = {
>     isa = Test
>   }
>   name = 0x0000000100003118 @"$"
>   value = 0x0000000100003118 @"$"
>   parent = nil
>   children = 0x0000000100305910 2 key/value pairs
> }
> (lldb) print *self->name
> (NSString) $1 = {
>   NSObject = {
>     isa = __NSCFConstantString
>   }
> }
> (lldb) print self->name
> (__NSCFConstantString *) $2 = 0x0000000100003118 @"$"
> 
> Wolfgang
> 
>