On Wed, Jul 03, 2019 at 02:46:14PM -0500, Josh Poimboeuf wrote: > On Wed, Jul 03, 2019 at 02:45:28PM -0500, Josh Poimboeuf wrote: > > On Wed, Jul 03, 2019 at 10:23:21AM -0700, Randy Dunlap wrote: > > > On 7/3/19 9:44 AM, Josh Poimboeuf wrote: > > > > On Tue, Jul 02, 2019 at 11:47:02AM -0700, Randy Dunlap wrote: > > > >> On 7/2/19 2:51 AM, Stephen Rothwell wrote: > > > >>> Hi all, > > > >>> > > > >>> Changes since 20190701: > > > >>> > > > >> > > > >> on x86_64: > > > >> > > > >> kernel/bpf/core.o: warning: objtool: ___bpf_prog_run()+0x22: can't find switch jump table > > > > > > > > I don't see it on current linux-next/master. Can you share the config > > > > and .o? > > > > > > > > > > This warning happened in 6 of 10 builds for 20190702. > > > > > > Today (20190703) I don't see it at all, but I see this instead: > > > kernel/bpf/core.o: warning: objtool: ___bpf_prog_run()+0xa3: sibling call from callable instruction with modified stack frame > > > > > > Kernel (rand)config file and .o file for 20190702 are attached. > > > > Thanks, I'm able to recreate the sibling call warning with a randconfig > > on today's linux-next. > > > > GCC is doing some funky stuff. With my randconfig, ___bpf_prog_run() > > has 166 indirect calls to its jump table. Seems (a bit!) excessive. > > s/calls/jumps/ obviously > > > > > I'll need to look into it. Hm, it looks like disabling CONFIG_RETPOLINE causes GCC to produce vastly different code here. Without retpolines, it's not shy at all about indirect jumps. -- Josh
