Re: [Xen-devel] [PATCH v2 1/3] livepach: Add .livepatch.hooks functions and test-case

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

> >> > @@ -70,7 +71,11 @@ struct payload {
> >> >      unsigned int nsyms;                  /* Nr of entries in .strtab 
> >> > and 
> >> > symbols. */
> >> >      struct livepatch_build_id id;        /* 
> >> > ELFNOTE_DESC(.note.gnu.build-id) of the payload. */
> >> >      struct livepatch_build_id dep;       /* 
> >> > ELFNOTE_DESC(.livepatch.depends). */
> >> > -    char name[XEN_LIVEPATCH_NAME_SIZE]; /* Name of it. */
> >> > +    livepatch_loadcall_t **load_funcs;   /* The array of funcs to call 
> >> > after */
> >> > +    livepatch_unloadcall_t **unload_funcs;/* load and unload of the 
> >> > payload. */
> >> 
> >> These both seem like they want a const in the middle.
> > 
> > I did that initially and found out that the calling ->load_funcs[i] resulted
> > in _no_ code being called.
> > 
> > I did not dig in the assembler output to figure out what happend, let me
> > do that now.
> 
> Indeed - I can't see how a const modifier here could alter whether
> or not the pointed to function gets called.

I did a diff on the pre-assemble part (-S) with and without const on the above
structs. With 'const' we get:

        call    spin_debug_disable
 .LVL163:
-       .loc 1 1093 0
-       cmpl    $0, 324(%rbx)
-       je      .L112
-       movl    $0, %r12d
-.LVL164:
-.L113:
-       .loc 1 1094 0
-       mov     %r12d, %edx
-       movq    312(%rbx), %rax
-       call    *(%rax,%rdx,8)
-       .loc 1 1093 0
-       addl    $1, %r12d
-.LVL165:
-       cmpl    %r12d, 324(%rbx)
-       ja      .L113
-.LVL166:
-.L112:

being removed.

I thought it may have to do with the function not returning anything. But
even after making the typedef return it still omitted the call 
data->load_funcs[i]();


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