Re: [Xen-devel] [PATCH v8.1 12/27] xsplice: Implement support for applying/reverting/replacing patches.

[Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>]

On Thu, Apr 21, 2016 at 12:44:41AM -0600, Jan Beulich wrote:
> >>> On 21.04.16 at 02:28, <konrad.wilk@xxxxxxxxxx> wrote:
> >> >+    ASSERT(sec);
> >> >+    if ( sec->sec->sh_size % sizeof(*payload->funcs) )
> >> >+    {
> >> >+        dprintk(XENLOG_ERR, XSPLICE "%s: Wrong size of 
> >> >.xsplice.funcs!\n",
> >> >+                elf->name);
> >> >+        return -EINVAL;
> >> >+    }
> >> >+
> >> >+    payload->funcs = sec->load_addr;
> >> >+    payload->nfuncs = sec->sec->sh_size / sizeof(*payload->funcs);
> >> 
> >> Following to our discussion yesterday - can't we (ab)use the section merge
> >> flag here to report the structure size, along the lines of what relocation
> >> sections do for their elements?
> > 
> > 
> > In other words - the xsplice-tools.git and the test-cases (in
> > arch/x86/xen/test) would modify the sec->sh_entsize to have the
> > sizeof(xsplice_patch_func) aka 64 (0x40) ?
> > 
> > [Note this could also extend to .xsplice.hooks.load and
> > .xsplice.hooks.unload]
> > 
> > The xsplice-tools.git could surely do it, but the built-in test-cases -
> > not so much. I would need to do some in-place binary handrolling - unless 
> > you
> > know of some tool or some __section modifiers?
> 
> Well, that's why I suggest (ab) using the SHF_MERGE flag, i.e. to
> see whether we can make gas do what we want. Fiddling with the
> binary I would not recommend, i.e. if we can't get gas to do what
> we want we should rather stay with what there is.

This:

diff --git a/xen/arch/x86/test/xen_hello_world.c 
b/xen/arch/x86/test/xen_hello_world.c
index a3da85d..92f2e97 100644
--- a/xen/arch/x86/test/xen_hello_world.c
+++ b/xen/arch/x86/test/xen_hello_world.c
@@ -47,6 +47,13 @@ XSPLICE_UNLOAD_HOOK(hi_func);
 
 XSPLICE_UNLOAD_HOOK(Z_check_fnc);
 
+#define XSPLICE_FUNC() \
+    asm ( \
+    ".pushsection .xsplice.funcs, \"awM\", @progbits, 64\n " \
+    ".popsection")
+
+XSPLICE_FUNC();
+
 struct xsplice_patch_func __section(".xsplice.funcs") xsplice_xen_hello_world 
= {
     .version = XSPLICE_PAYLOAD_VERSION,
     .name = hello_world_patch_this_fnc,

Makes the .xsplice.funcs have sh_entsize have the size of 64 bytes:


  [ 6] .xsplice.funcs    PROGBITS         0000000000000000  000000a0
       0000000000000040  0000000000000000  WA       0     0     32
vs

  [ 6] .xsplice.funcs    PROGBITS         0000000000000000  000000a0
       0000000000000040  0000000000000040 WAM       0     0     32

Unfortunatly the compilation throws this:

FC-64 <konrad@build-external:~/xtt-x86_64/xen/xen> make -j4 tests 1>1
dnsdomainname: Name or service not known
{standard input}: Assembler messages:
{standard input}:184: Warning: ignoring changed section attributes for 
.xsplice.funcs


This is with:
binutils-2.20.51.0.2-15.fc13.x86_64
and with:
binutils-2.25-9.fc22.x86_64

Ideas?

I could try to wrap the definition of these
struct xsplice_patch_func __section(".xsplice.funcs") xsplice_xen_hello_world 
using an macro - but that did not work very well (I couldn't manage it
to take the value of say XSPLICE_PAYLOAD_VERSION).

Perhaps skip this?
> 
> Jan
> 

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