Re: [PATCH] [gdb/testsuite] Fix gdb.dwarf2/dw2-entry-points.exp on ppc64le

[Tom de Vries <tdevries@suse.de>]

On 1/11/24 13:55, Guinevere Larsen wrote:
> On 11/01/2024 13:42, Tom de Vries wrote:
>> On ppc64le-linux, I run into:
>> ...
>> (gdb) bt^M
>>   #0  0x00000000100006dc in foobar (J=2)^M
>>   #1  0x000000001000070c in prog ()^M
>> (gdb) FAIL: gdb.dwarf2/dw2-entry-points.exp: bt foo
>> ...
>>
>> The test-case attemps to emulate additional entry points of a 
>> function, with
>> function bar having entry points foo and foobar:
>> ...
>> (gdb) p bar
>> $1 = {void (int, int)} 0x1000064c <bar>
>> (gdb) p foo
>> $2 = {void (int, int)} 0x10000698 <foo>
>> (gdb) p foobar
>> $3 = {void (int)} 0x100006d0 <foobar>
>> ...
>>
>> However, when setting a breakpoint on the entry point foo:
>> ...
>> (gdb) b foo
>> Breakpoint 1 at 0x100006dc
>> ...
>> it ends up in foobar instead of in foo, due to prologue skipping, and
>> consequently the backtrace show foobar instead foo.
>>
>> The problem is that the test-case does not emulate an actual prologue 
>> at each
>> entry point.
>>
>> Fix this by disabling the prologue skipping when setting a breakpoint, 
>> using
>> "break *foo".
> 
> Sorry if my question doesn't make sense, but wouldn't we also want to 
> verify that prologue skipping works correctly in a function with 
> multiple entrypoints?
> 

Agreed, ideally we'd also verify it in this test-case.

However, the commit introducing support for this also adds a test-case 
gdb.fortran/entry-point.exp which does verify that part of the 
functionality with compiler-generated entry points and prologues.

> I agree that this looks like a testsuite fail rather than a real GDB 
> bug, but I feel like we'll be losing a valuable test if we don't try it 
> at any point, especially now that it is easy to explicitly mark an 
> instruction as EPILOGUE_END in the dwarf assembler.
> 

I suppose you mean prologue_end (and I hadn't thought of that, thanks 
for the suggestion), but yes, we could do this.  It would require adding 
a .debug_line section in the dwarf assembly, something that is currently 
missing.

But given that the other test-case already tests this functionality, I'm 
not sure if it's worth the effort.

Thanks,
- Tom