changes to .kprobes.text not detected

[jpoimboe]

With the following patch, kpatch-build doesn't detect any changes:

~ $ cat ~/nmi.patch 
Index: src/arch/x86/kernel/nmi.c
===================================================================
--- src.orig/arch/x86/kernel/nmi.c
+++ src/arch/x86/kernel/nmi.c
@@ -518,6 +518,8 @@ do_nmi(struct pt_regs *regs, long error_

    inc_irq_stat(__nmi_count);

+   printk("nmi\n");
+
    if (!ignore_nmis)
        default_do_nmi(regs);

~ $ kpatch-build -d nmi.patch 
DEBUG mode enabled
Using cache at /home/jpoimboe/.kpatch/3.13.10-200.fc20.x86_64/src
Testing patch file
patching file arch/x86/kernel/nmi.c
Building original kernel
Building patched kernel
Detecting changed objects
Rebuilding changed objects
Extracting new and modified ELF sections
nmi.o: no changed functions were found
ERROR: kpatch build failed. Check /tmp/kpatch-build-1398776924.log for more details.

I think it's because do_nmi() is annotated with __kprobes which places it in the .kprobes.text section. But I'd expect the inclusion logic to catch the fact that .kprobes.text changed and report an error.

[jpoimboe]

Hm, maybe the "no changed functions were found" check happens before the "some unexpected section changed" check?

[jpoimboe]

Yeah, with a bigger patch that changes another non-kprobes function, I get the error I expected:

~ $ cat nmi.patch 
Index: src/arch/x86/kernel/nmi.c
===================================================================
--- src.orig/arch/x86/kernel/nmi.c
+++ src/arch/x86/kernel/nmi.c
@@ -146,6 +146,8 @@ int __register_nmi_handler(unsigned int
    if (!action->handler)
        return -EINVAL;

+   printk("a\n");
+
    spin_lock_irqsave(&desc->lock, flags);

    /*
@@ -518,6 +520,8 @@ do_nmi(struct pt_regs *regs, long error_

    inc_irq_stat(__nmi_count);

+   printk("nmi\n");
+
    if (!ignore_nmis)
        default_do_nmi(regs);

~ $ kpatch-build nmi.patch 
Using cache at /home/jpoimboe/.kpatch/3.13.10-200.fc20.x86_64/src
Testing patch file
patching file arch/x86/kernel/nmi.c
Building original kernel
Building patched kernel
Detecting changed objects
Rebuilding changed objects
Extracting new and modified ELF sections
nmi.o: changed function: __register_nmi_handler
nmi.o: changed function: unregister_nmi_handler
nmi.o: changed section .kprobes.text not selected for inclusion
/usr/local/libexec/kpatch/create-diff-object: unreconcilable difference
ERROR: kpatch build failed. Check /tmp/kpatch-build-1398785999.log for more details.