[Xen-devel] [PATCH v2 LIVEPATCH-BUILD-TOOLS] Fix patch creation with GCC 6.1+

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

GCC 6.1+ fixed https://gcc.gnu.org/bugzilla/show_bug.cgi?id=192 which
means that .rodata.str1.[0-9]+ sections are now split by function.  We
could probably be smarter about including just the sections we need, but
for now, simply include the string sections for all functions as is done
for previous versions of GCC.

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
Reported-by: M A Young <m.a.young@xxxxxxxxxxxx>
---

Changed in v2:
* Clarified commit message.

 create-diff-object.c | 39 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/create-diff-object.c b/create-diff-object.c
index 69bcd88..b0d1348 100644
--- a/create-diff-object.c
+++ b/create-diff-object.c
@@ -1184,6 +1184,43 @@ static void kpatch_process_special_sections(struct 
kpatch_elf *kelf)
        }
 }
 
+/* Returns true if s is a string of only numbers with length > 0. */
+static int isnumber(const char *s)
+{
+       do {
+               if (!*s || !isdigit(*s))
+                       return 0;
+       } while (*++s);
+
+       return 1;
+}
+
+/*
+ * String sections are always included even if unchanged.
+ * The format is either:
+ * .rodata.<func>.str1.[0-9]+ (new in GCC 6.1.0)
+ * or .rodata.str1.[0-9]+ (older versions of GCC)
+ * For the new format we could be smarter and only include the needed
+ * strings sections.
+ */
+static int should_include_str_section(const char *name)
+{
+       const char *s;
+
+       if (strncmp(name, ".rodata.", 8))
+               return 0;
+
+       /* Check if name matches ".rodata.str1.[0-9]+" */
+       if (!strncmp(name, ".rodata.str1.", 13))
+               return isnumber(name + 13);
+
+       /* Check if name matches ".rodata.<func>.str1.[0-9]+" */
+       s = strstr(name, ".str1.");
+       if (!s)
+               return 0;
+       return isnumber(s + 6);
+}
+
 static void kpatch_include_standard_elements(struct kpatch_elf *kelf)
 {
        struct section *sec;
@@ -1193,7 +1230,7 @@ static void kpatch_include_standard_elements(struct 
kpatch_elf *kelf)
                if (!strcmp(sec->name, ".shstrtab") ||
                    !strcmp(sec->name, ".strtab") ||
                    !strcmp(sec->name, ".symtab") ||
-                   !strncmp(sec->name, ".rodata.str1.", 13)) {
+                   should_include_str_section(sec->name)) {
                        sec->include = 1;
                        if (sec->secsym)
                                sec->secsym->include = 1;
-- 
2.7.4


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