[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH 3/7] x86/dom0: placate GCC 12 compile-time errors with UBSAN and PVH_GUEST
On Fri, Mar 14, 2025 at 09:33:01AM +0100, Jan Beulich wrote: > On 14.03.2025 09:27, Roger Pau Monné wrote: > > On Fri, Mar 14, 2025 at 09:10:59AM +0100, Jan Beulich wrote: > >> On 13.03.2025 16:30, Roger Pau Monne wrote: > >>> When building Xen with GCC 12 with UBSAN and PVH_GUEST both enabled the > >>> compiler emits the following errors: > >>> > >>> arch/x86/setup.c: In function '__start_xen': > >>> arch/x86/setup.c:1504:19: error: 'consider_modules' reading 40 bytes from > >>> a region of size 4 [-Werror=stringop-overread] > >>> 1504 | end = consider_modules(s, e, reloc_size + mask, > >>> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >>> 1505 | bi->mods, bi->nr_modules, -1); > >>> | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >>> arch/x86/setup.c:1504:19: note: referencing argument 4 of type 'const > >>> struct boot_module[0]' > >>> arch/x86/setup.c:686:24: note: in a call to function 'consider_modules' > >>> 686 | static uint64_t __init consider_modules( > >>> | ^~~~~~~~~~~~~~~~ > >>> arch/x86/setup.c:1535:19: error: 'consider_modules' reading 40 bytes from > >>> a region of size 4 [-Werror=stringop-overread] > >>> 1535 | end = consider_modules(s, e, size, bi->mods, > >>> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >>> 1536 | bi->nr_modules + relocated, j); > >>> | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >>> arch/x86/setup.c:1535:19: note: referencing argument 4 of type 'const > >>> struct boot_module[0]' > >>> arch/x86/setup.c:686:24: note: in a call to function 'consider_modules' > >>> 686 | static uint64_t __init consider_modules( > >>> | ^~~~~~~~~~~~~~~~ > >>> > >>> This seems to be the result of some function manipulation done by UBSAN > >>> triggering GCC stringops related errors. Placate the errors by declaring > >>> the function parameter as `const struct *boot_module` instead of `const > >>> struct boot_module[]`. > >>> > >>> Note that GCC 13 seems to be fixed, and doesn't trigger the error when > >>> using `[]`. > >>> > >>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> > >>> --- > >>> xen/arch/x86/setup.c | 2 +- > >>> 1 file changed, 1 insertion(+), 1 deletion(-) > >>> > >>> diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c > >>> index 4a32d8491186..bde5d75ea6ab 100644 > >>> --- a/xen/arch/x86/setup.c > >>> +++ b/xen/arch/x86/setup.c > >>> @@ -684,7 +684,7 @@ static void __init noinline move_xen(void) > >>> #undef BOOTSTRAP_MAP_LIMIT > >>> > >>> static uint64_t __init consider_modules( > >>> - uint64_t s, uint64_t e, uint32_t size, const struct boot_module > >>> mods[], > >>> + uint64_t s, uint64_t e, uint32_t size, const struct boot_module > >>> *mods, > >>> unsigned int nr_mods, unsigned int this_mod) > >>> { > >>> unsigned int i; > >> > >> While I'm okay-ish with the change, how are we going to make sure it won't > >> be > >> re-introduced? Or something similar be introduced elsewhere? > > > > I'm afraid I don't have a good response, as I don't even know exactly > > why the error triggers. > > One option might be to amend ./CODING_STYLE for dis-encourage [] notation > in function parameters. I wouldn't be happy about us doing so, as I think > that serves a documentation purpose, but compiler deficiencies getting in > the way is certainly higher priority here. > > Trying to abstract this (vaguely along the lines of gcc11_wrap()), otoh, > wouldn't be desirable imo, as it would still lose the doc effect, at least > to some degree. This is a very specific case, I don't think we should change our coding style based on it. I think our only option is to deal with such compiler bugs when we detect them. Thanks, Roger.
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