Hi, Thanks for your review and patient. On 2022/6/23 16:13, Marc Zyngier wrote: > On 2022-06-23 02:49, Chen Zhongjin wrote: >> Using unreachable() at default of switch generates an extra branch at >> end of the function, and compiler won't generate a ret to close this >> branch because it knows it's unreachable. >> >> If there's no instruction in this branch, compiler will generate a NOP, >> And it will confuse objtool to warn this NOP as a fall through branch. >> >> In fact these branches are actually unreachable, so we can replace >> unreachable() with returning a -EINVAL value. >> >> Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx> >> --- >> arch/arm64/kvm/hyp/vgic-v3-sr.c | 7 +++---- >> drivers/irqchip/irq-gic-v3.c | 2 +- >> 2 files changed, 4 insertions(+), 5 deletions(-) > > Basic courtesy would have been to Cc the maintainers of this code. > Sorry for that. I'll cc everyone next time. >> >> diff --git a/arch/arm64/kvm/hyp/vgic-v3-sr.c b/arch/arm64/kvm/hyp/vgic-v3-sr.c >> index 4fb419f7b8b6..f3cee92c3038 100644 >> --- a/arch/arm64/kvm/hyp/vgic-v3-sr.c >> +++ b/arch/arm64/kvm/hyp/vgic-v3-sr.c >> @@ -6,7 +6,6 @@ >> >> #include <hyp/adjust_pc.h> >> >> -#include <linux/compiler.h> >> #include <linux/irqchip/arm-gic-v3.h> >> #include <linux/kvm_host.h> >> >> @@ -55,7 +54,7 @@ static u64 __gic_v3_get_lr(unsigned int lr) >> return read_gicreg(ICH_LR15_EL2); >> } >> >> - unreachable(); >> + return -EINVAL; > > NAK. That's absolutely *wrong*, and will hide future bugs. > Nothing checks for -EINVAL, and we *never* expect to > reach this, hence the perfectly valid annotation. > > If something needs fixing, it probably is your tooling. > > M. You are right. Essentially, this is because objtool does not anticipate that the compiler will generate additional instructions when marking unreachable instructions. I'll fix this problem or add a specific check for this state. Best, Chen
