+Aaron, please read up on this discussion, and step in if you can help. (Aaron is the DPDK Project testing leader, and works at Red Hat.)
> From: Scott Mitchell [mailto:[email protected]] > Sent: Friday, 9 January 2026 05.58 > > On Thu, Jan 8, 2026 at 7:01 PM Stephen Hemminger > <[email protected]> wrote: > > > > On Thu, 8 Jan 2026 16:19:37 -0500 > > Scott Mitchell <[email protected]> wrote: > > > > > On Thu, Jan 8, 2026 at 11:12 AM Stephen Hemminger > > > <[email protected]> wrote: > > > > > > > > On Thu, 8 Jan 2026 01:13:38 -0500 > > > > [email protected] wrote: > > > > > > > > > +#ifdef RTE_CC_GCC > > > > > + /* Suppress GCC -Wmaybe-uninitialized false positive. No > assembly/runtime impacts. */ > > > > > + asm volatile("" : "+m" (psd_hdr)); > > > > > +#endif > > > > > > > > > > > > > Maybe rte_compiler_barrier() will do same thing? > > > > > > Agreed it feels like a compiler bug but looking for advice if I'm > > > missing something :) > > > > > > My initial concern with rte_compiler_barrier is its a general > barrier > > > which may have broader impacts on > > > optimizations and compiled code. Will that be an issue in this > case? I > > > wasn't sure and the approach > > > in the patch is targeted at a specific variable and assembly from > > > clang/gcc was the same. I will > > > introduce a macro to make it cleaner and I can replace it with > > > rte_compiler_barrier if preferred. > > > > Maybe try with -fanalyzer and it might tell you more. > > I suspect some of the aliasing setting are causing issues. > > Some drivers are turning on no-strict-aliasing > > I have more evidence this is a GCC optimizer bug. > The RTE_SUPPRESS_UNINITIALIZED_WARNING approach serves > as a workaround to avoid the bug. I created a more minimal reproducer: > https://gist.github.com/Scottmitch/bf23748b4588e68c9bdb8d124f92f1bd > > Your suspicion was correct, -fno-strict-aliasing avoids the bug but I > don't > think it is desirable to enable this broadly for DPDK when we have a > more targeted workaround. > > I will reach out to RH to confirm but in the interim I suggest we keep > RTE_SUPPRESS_UNINITIALIZED_WARNING (or similar alternative). If this is a GCC compiler bug limited to the GCC version offered by RHEL 11, I prefer splitting the patch into a series with the following steps: Patch 1/2: Add the optimization and new test cases in their minimal form, designed to work on normal compilers. Disregard bugs/warnings from the weird RHEL 11 compiler. I.e. don't modify lib/eal/include/rte_common.h, lib/net/rte_ip6.h, lib/net/rte_ip4.h, drivers/net/hinic/hinic_pmd_tx.c, drivers/net/mlx5/mlx5_flow_dv.c. Patch 2/2: Add the workarounds required by the RHEL 11 compiler. Also, the change to drivers/net/hinic/hinic_pmd_tx.c should be moved to a patch independent of this series. It's not directly related to this series, so let's not add more to the discussion than we need to. ;-) And the implementation in the driver only considers RTE_MBUF_F_TX_TCP_SEG, whereas the DPDK function also considers RTE_MBUF_F_TX_UDP_SEG, so it warrants a separate discussion; it possibly fixes a bug. Maybe even move the RHEL 11 related patches (my suggested patch 2/2) into a separate series, for the same conceptual reasons as moving the HINIC driver patch into a separate series. You can use the Depends-On tag (https://doc.dpdk.org/guides/contributing/patches.html#patch-dependencies) for the follow-on changes to __rte_raw_cksum().
