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Re: [Xen-devel] [livepatch-build-tools part2 5/6] create-diff-object: Add new entries to special sections array



On 4/16/19 1:07 PM, Pawel Wieczorkiewicz wrote:
Handle .livepatch.hooks* and .altinstr_replacement sections as the
special sections with assigned group_size resolution function.
By default each .livepatch.hooks* sections' entry is 8 bytes long (a
pointer). The .altinstr_replacement section follows the .altinstructions
section settings.

Allow to specify different .livepatch.hooks* section entry size using
shell environment variable HOOK_STRUCT_SIZE.

Cleanup an incorrect indentation around group_size resulution functions.

Signed-off-by: Pawel Wieczorkiewicz <wipawel@xxxxxxxxx>
Reviewed-by: Andra-Irina Paraschiv <andraprs@xxxxxxxxxx>
Reviewed-by: Bjoern Doebel <doebel@xxxxxxxxx>
Reviewed-by: Norbert Manthey <nmanthey@xxxxxxxxx>
---
  create-diff-object.c | 87 ++++++++++++++++++++++++++++++++--------------------
  1 file changed, 54 insertions(+), 33 deletions(-)

diff --git a/create-diff-object.c b/create-diff-object.c
index b0b4dcb..f6060cd 100644
--- a/create-diff-object.c
+++ b/create-diff-object.c
@@ -960,51 +960,64 @@ static void kpatch_mark_constant_labels_same(struct 
kpatch_elf *kelf)

Fix the indentation in the patch which introduces the problem rather than fixing it in a subsequent patch.

static int bug_frames_group_size(struct kpatch_elf *kelf, int offset)
  {
-    static int size = 0;
-    char *str;
-    if (!size) {
-        str = getenv("BUG_STRUCT_SIZE");
-        size = str ? atoi(str) : 8;
-    }
-
-    return size;
+       static int size = 0;
+       char *str;
+       if (!size) {
+               str = getenv("BUG_STRUCT_SIZE");
+               size = str ? atoi(str) : 8;
+       }
+
+       return size;
  }
static int bug_frames_3_group_size(struct kpatch_elf *kelf, int offset)
  {
-    static int size = 0;
-    char *str;
-    if (!size) {
-        str = getenv("BUG_STRUCT_SIZE");
-        size = str ? atoi(str) : 16;
-    }
-
-    return size;
+       static int size = 0;
+       char *str;
+       if (!size) {
+               str = getenv("BUG_STRUCT_SIZE");
+               size = str ? atoi(str) : 16;
+       }
+
+       return size;
  }
static int ex_table_group_size(struct kpatch_elf *kelf, int offset)
  {
-    static int size = 0;
-    char *str;
-    if (!size) {
-        str = getenv("EX_STRUCT_SIZE");
-        size = str ? atoi(str) : 8;
-    }
-
-    return size;
+       static int size = 0;
+       char *str;
+       if (!size) {
+               str = getenv("EX_STRUCT_SIZE");
+               size = str ? atoi(str) : 8;
+       }
+
+       return size;
  }
static int altinstructions_group_size(struct kpatch_elf *kelf, int offset)
  {
-    static int size = 0;
-    char *str;
-    if (!size) {
-        str = getenv("ALT_STRUCT_SIZE");
-        size = str ? atoi(str) : 12;
-    }
-
-    printf("altinstr_size=%d\n", size);
-    return size;
+       static int size = 0;
+       char *str;
+       if (!size) {
+               str = getenv("ALT_STRUCT_SIZE");
+               size = str ? atoi(str) : 12;
+       }
+
+       printf("altinstr_size=%d\n", size);
+       return size;
+}
+
+static int livepatch_hooks_group_size(struct kpatch_elf *kelf, int offset)
+{
+       static int size = 0;
+       char *str;
+       if (!size) {
+               str = getenv("HOOK_STRUCT_SIZE");
+               size = str ? atoi(str) : 8;
+       }
+
+       printf("livepatch_hooks_size=%d\n", size);

If you want to keep this debugging output, rather use log_debug().

+       return size;
  }
/*
@@ -1084,6 +1097,14 @@ static struct special_section special_sections[] = {
                .name           = ".altinstructions",
                .group_size     = altinstructions_group_size,
        },
+       {
+               .name           = ".altinstr_replacement",
+               .group_size     = altinstructions_group_size,
+       },
+       {
+               .name           = ".livepatch.hooks",
+               .group_size     = livepatch_hooks_group_size,
+       },
        {},
  };

I don't understand the point of this change.

IIUC unlike .altinstructions, the .altinstr_replacement section does not have a fixed group size, so this change would not work other than by luck. If the goal was to prune bits of the .altinstr_replacement table that do not need to be included, you need to update the code in kpatch_process_special_sections() which has special handling for .altinstr_replacement. It needs to parse the updated, pruned .altinstructions section and regenerate .altinstr_replacement, including only what is needed.

I don't know why .livepatch.hooks is included in this list either since all hooks are always included and there is nothing to regenerate/prune.

Regards,
--
Ross Lagerwall

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