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Re: [Xen-devel] [livepatch-build-tools part2 4/6] livepatch-build: detect special section group sizes
On 4/29/19 3:10 PM, Ross Lagerwall wrote:
On 4/16/19 1:07 PM, Pawel Wieczorkiewicz wrote:
Hard-coding the special section group sizes is unreliable. Instead,
determine them dynamically by finding the related struct definitions
in the DWARF metadata.
This is a livepatch backport of kpatch upstream commit [1]:
kpatch-build: detect special section group sizes 170449847136a48b19fc
Xen only deals with alt_instr, bug_frame and exception_table_entry
structures, so sizes of these structers are obtained from xen-syms.
structers -> structures
This change is needed since with recent Xen the alt_instr structure
has changed size from 12 to 14 bytes.
[1]
https://github.com/jpoimboe/kpatch/commit/170449847136a48b19fcceb19c1d4d257d386b56
Signed-off-by: Pawel Wieczorkiewicz <wipawel@xxxxxxxxx>
Reviewed-by: Bjoern Doebel <doebel@xxxxxxxxx>
Reviewed-by: Martin Mazein <amazein@xxxxxxxxx>
---
create-diff-object.c | 60
++++++++++++++++++++++++++++++++++++++++++++--------
livepatch-build | 23 ++++++++++++++++++++
2 files changed, 74 insertions(+), 9 deletions(-)
diff --git a/create-diff-object.c b/create-diff-object.c
index 1e6e617..b0b4dcb 100644
--- a/create-diff-object.c
+++ b/create-diff-object.c
@@ -958,12 +958,54 @@ static void
kpatch_mark_constant_labels_same(struct kpatch_elf *kelf)
}
}
-static int bug_frames_0_group_size(struct kpatch_elf *kelf, int
offset) { return 8; }
-static int bug_frames_1_group_size(struct kpatch_elf *kelf, int
offset) { return 8; }
-static int bug_frames_2_group_size(struct kpatch_elf *kelf, int
offset) { return 8; }
-static int bug_frames_3_group_size(struct kpatch_elf *kelf, int
offset) { return 16; }
-static int ex_table_group_size(struct kpatch_elf *kelf, int offset) {
return 8; }
-static int altinstructions_group_size(struct kpatch_elf *kelf, int
offset) { return 12; }
+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;
Why did you remove the hard error here from the original kpatch commit?
I think a hard error is preferable to guessing.
+ }
+
+ 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 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 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;
+}
/*
* The rela groups in the .fixup section vary in size. The
beginning of each
@@ -1016,15 +1058,15 @@ static int fixup_group_size(struct kpatch_elf
*kelf, int offset)
static struct special_section special_sections[] = {
{
.name = ".bug_frames.0",
- .group_size = bug_frames_0_group_size,
+ .group_size = bug_frames_group_size,
},
{
.name = ".bug_frames.1",
- .group_size = bug_frames_1_group_size,
+ .group_size = bug_frames_group_size,
},
{
.name = ".bug_frames.2",
- .group_size = bug_frames_2_group_size,
+ .group_size = bug_frames_group_size,
},
{
.name = ".bug_frames.3",
diff --git a/livepatch-build b/livepatch-build
index c057fa1..a6cae12 100755
--- a/livepatch-build
+++ b/livepatch-build
@@ -284,6 +284,29 @@ echo "Output directory: ${OUTPUT}"
echo "================================================"
echo
+if [ -f "$XENSYMS" ]; then
+ echo "Reading special section data"
+ SPECIAL_VARS=$(readelf -wi "$XENSYMS" |
+ gawk --non-decimal-data '
+ BEGIN { a = b = e = 0 }
+ a == 0 && /DW_AT_name.* alt_instr/ {a = 1; next}
+ b == 0 && /DW_AT_name.* bug_frame/ {b = 1; next}
+ e == 0 && /DW_AT_name.* exception_table_entry/ {e = 1;
next}
+ a == 1 {printf("export ALT_STRUCT_SIZE=%d\n", $4); a = 2}
+ b == 1 {printf("export BUG_STRUCT_SIZE=%d\n", $4); b = 2}
+ e == 1 {printf("export EX_STRUCT_SIZE=%d\n", $4); e = 2}
+ a == 2 && b == 2 && e == 2 {exit}')
+ [[ -n $SPECIAL_VARS ]] && eval "$SPECIAL_VARS"
+ if [[ -z $ALT_STRUCT_SIZE ]] || [[ -z $BUG_STRUCT_SIZE ]] || [[
-z $EX_STRUCT_SIZE ]]; then
+ die "can't find special struct size"
+ fi
+ for i in $ALT_STRUCT_SIZE $BUG_STRUCT_SIZE $EX_STRUCT_SIZE; do
+ if [[ ! $i -gt 0 ]] || [[ ! $i -le 16 ]]; then
+ die "invalid special struct size $i"
+ fi
+ done
+fi
+
If this hunk is moved after the call to build_full(), then it can be run
directly on the xen-syms that has just been built which would allow
dropping `if [ -f "$XENSYMS" ]...` and guaranteeing that *_STRUCT_SIZE
are always set.
One more thing, previously:
bug_frames_0_group_size == 8
bug_frames_1_group_size == 8
bug_frames_2_group_size == 8
bug_frames_3_group_size == 16
And now:
bug_frames_0_group_size == BUG_STRUCT_SIZE
bug_frames_1_group_size == BUG_STRUCT_SIZE
bug_frames_2_group_size == BUG_STRUCT_SIZE
bug_frames_3_group_size == BUG_STRUCT_SIZE
This seems wrong to me. When reading special section data, should you
detect e.g. BUG0_STRUCT_SIZE, BUG1_STRUCT_SIZE, ... ?
--
Ross Lagerwall
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