[PATCH v2 3/3] livepatch: Sync cache of build-id before using it first time.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

We don't print at bootup time the build-id. The reason is
that xen_build_init and livepatch_init are both __initcall
type routines. This meant that when livepatch_init called
xen_build_id, it would return -ENODATA as build_id_len was
not setup yet (b/c xen_build_init would be called later).

We fix this by calling xen_build_init in livepatch_init which
allows us to print the build-id of the hypervisor.

We also keep xen_build_init as __initcall because build-id
can be built without livepatching being enabled (so
no livepatch_init being called).

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

---
Cc: Ross Lagerwall <ross.lagerwall@citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
---
 xen/common/livepatch.c      | 1 +
 xen/common/version.c        | 6 +++++-
 xen/include/xen/livepatch.h | 2 +-
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/xen/common/livepatch.c b/xen/common/livepatch.c
index f6dbd51..88a79d8 100644
--- a/xen/common/livepatch.c
+++ b/xen/common/livepatch.c
@@ -1597,6 +1597,7 @@ static int __init livepatch_init(void)
     const void *binary_id;
     unsigned int len;
 
+    xen_build_init();
     if ( !xen_build_id(&binary_id, &len) )
         printk(XENLOG_INFO LIVEPATCH ": build-id: %*phN\n", len, binary_id);
 
diff --git a/xen/common/version.c b/xen/common/version.c
index 0f96849..4114664 100644
--- a/xen/common/version.c
+++ b/xen/common/version.c
@@ -117,11 +117,15 @@ int xen_build_id_check(const Elf_Note *n, unsigned int n_sz,
     return 0;
 }
 
-static int __init xen_build_init(void)
+int __init xen_build_init(void)
 {
     const Elf_Note *n = __note_gnu_build_id_start;
     unsigned int sz;
 
+    /* We may have been called already. */
+    if ( build_id_len )
+        return 0;
+
     /* --build-id invoked with wrong parameters. */
     if ( __note_gnu_build_id_end <= &n[0] )
         return -ENODATA;
diff --git a/xen/include/xen/livepatch.h b/xen/include/xen/livepatch.h
index ed49843..cfc9601 100644
--- a/xen/include/xen/livepatch.h
+++ b/xen/include/xen/livepatch.h
@@ -44,7 +44,7 @@ unsigned long livepatch_symbols_lookup_by_name(const char *symname);
 bool_t is_patch(const void *addr);
 int xen_build_id_check(const Elf_Note *n, unsigned int n_sz,
                        const void **p, unsigned int *len);
-
+void xen_build_init(void);
 /* Arch hooks. */
 int arch_livepatch_verify_elf(const struct livepatch_elf *elf);
 int arch_livepatch_perform_rel(struct livepatch_elf *elf,
-- 
2.5.5


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