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create-diff-object: fix Clang UBSAN diff failure by ignoring unnamed data #1485

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create-diff-object: fix Clang UBSAN diff failure by ignoring unnamed data #1485

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20 changes: 20 additions & 0 deletions kpatch-build/create-diff-object.c
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Original file line number Diff line number Diff line change
Expand Up @@ -396,6 +396,17 @@ static bool is_string_literal_section(struct section *sec)
return !strncmp(sec->name, ".rodata.", 8) && strstr(sec->name, ".str");
}

/*
* Clang generates .data..L__unnamed_XX sections for anonymous constants.
* The numeric suffix is unstable (it can change if code is added/removed).
* Therefore, we must never correlate these by name; the patched object
* must always allocate a fresh copy (Status: NEW).
*/
static bool is_clang_unnamed_data(const char *name)
{
return !strncmp(name, ".data..L__unnamed_", 18);
}

/*
* This function detects whether the given symbol is a "special" static local
* variable (for lack of a better term).
Expand Down Expand Up @@ -425,6 +436,10 @@ static bool is_special_static(struct symbol *sym)
if (is_dynamic_debug_symbol(sym))
return true;

/* Do not try to correlate statics inside unstable Clang sections */
if (sym->sec && is_clang_unnamed_data(sym->sec->name))
return true;

if (sym->type == STT_SECTION) {
/* make sure section is bundled */
if (!sym->sec->sym)
Expand Down Expand Up @@ -1142,6 +1157,11 @@ static void kpatch_correlate_sections(struct list_head *seclist_orig,
if (is_ubsan_sec(sec_orig->name))
continue;

/* Skip correlation for unstable Clang anonymous sections */
if (is_clang_unnamed_data(sec_orig->name) ||
is_clang_unnamed_data(sec_patched->name))
continue;

if (is_special_static(is_rela_section(sec_orig) ?
sec_orig->base->secsym :
sec_orig->secsym))
Expand Down