Re: [Patch] LTO: Fix writing of toplevel asm with offloading [PR109816]

[Thomas Schwinge <thomas@codesourcery.com>]

Hi!

On 2023-05-12T14:46:21+0200, Tobias Burnus <tobias@codesourcery.com> wrote:
> Long standing issue but as top-level 'asm' statement were rare, it did not show up.

Thanks for tracking this down, and fixing it!  Presumably latent
"forever" (here: since code offloading support was added, approximately
one decade ago).

> However, the fix for PR108969 in commit r14-321-g9a41d2cdbcd added code
>
> +#elif defined(_GLIBCXX_SYMVER_GNU)
> +  __extension__ __asm (".globl _ZSt21ios_base_library_initv");
> q
> libstdc++-v3/include/std/iostream. This was then duly written by the offloading-device
> lto1 for digestion by the device-target assembler. While the llvm-mc linker user by
> GCN did accept .globl, nvptx's ptxas did choke on it.
>
> Additionally, as the assembly was already written for offloading, the output was
> lost on the host when using LTO for not only for offload but for real (i.e. with -flto).

> Has someone an idea how to check whether the offloading-code assembler does not
> contain the _ZSt21ios_base_library_initv while the host-side (before or after LTO)
> should contain it, but only with _GLIBCXX_SYMVER_GNU?
> Otherwise, the testcase tests only and at least whether it breaks with nvptx
> as ptxas does not like the symbol.

We can construct test cases with their own top-level 'asm', outside of
the libstdc++ context?  I'll try to come up with something.


> The installed-build regtesting of "make check-target-libgomp" seems to be currently broken
> as it does run all checking code (check_effective_target...) but does not seem to find
> any actual testcase to be run, probably a side effect of the recent testsuite changes.

FUD.  ;-O

We've since determined that Tobias' testing problem was due to
'//net/[...]' (double-slash) paths usage (with '/net' served by
'/etc/auto.master:/net -hosts'), which apparently confused DejaGnu/TCL
'find' (as used in 'libgomp/testsuite/libgomp.*/*.exp').

Per
<https://inbox.sourceware.org/877cte9cfa.fsf@euler.schwinge.homeip.net>:

| By the way, all changes (individually) tested in a number of different
| configurations: '--enable-languages=[...]', native vs. cross, build-tree
| vs. installed testing, etc.


Grüße
 Thomas
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