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

[Guinevere Larsen <blarsen@redhat.com>]

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?

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.

-- 
Cheers,
Guinevere Larsen
She/Her/Hers

>
> Tested on ppc64le-linux and x86_64-linux.
>
> PR testsuite/31232
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31232
> ---
>   gdb/testsuite/gdb.dwarf2/dw2-entry-points.exp | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/gdb/testsuite/gdb.dwarf2/dw2-entry-points.exp b/gdb/testsuite/gdb.dwarf2/dw2-entry-points.exp
> index f361820f72f..035b15ee087 100644
> --- a/gdb/testsuite/gdb.dwarf2/dw2-entry-points.exp
> +++ b/gdb/testsuite/gdb.dwarf2/dw2-entry-points.exp
> @@ -180,8 +180,8 @@ if ![runto_main] {
>   }
>   
>   # Try whether we can set and hit breakpoints at the entry_points.
> -gdb_breakpoint "foo"
> -gdb_breakpoint "foobar"
> +gdb_breakpoint "*foo"
> +gdb_breakpoint "*foobar"
>   
>   # Now hit the entry_point break point and check their call-stack.
>   gdb_continue_to_breakpoint "foo"
> @@ -204,7 +204,7 @@ if ![runto_main] {
>       return -1
>   }
>   
> -gdb_breakpoint "fooso"
> +gdb_breakpoint "*fooso"
>   gdb_continue_to_breakpoint "foo_so"
>   
>   gdb_test "bt" [multi_line \
>
> base-commit: 4ece39c56cfdd5647d4061f3c084b9de6f9e443c