[Xen-devel] [PATCH 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.str* sections are now split by function.  We could
probably be smarter about including just the sections we need, but for
now, include all .rodata.str* sections as is done for previous versions
of GCC.

This manifests itself as symbol error. E.g.:
(XEN)  Unknown symbol: .LC0

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