[ELF] --icf: do not fold preemptible symbols
Fixes PR44124.
A preemptible symbol may refer to a different definition at runtime.
When comparing a pair of relocations, if they refer to different
symbols, and either symbol is preemptible, the two containing sections
should be considered different.
gold has a similar rule https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=ce97fa81e0c46d216b80b143ad8c02fff6906fef
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D71163
diff --git a/lld/ELF/Symbols.cpp b/lld/ELF/Symbols.cpp
index cb5b52e..b5adbdc 100644
--- a/lld/ELF/Symbols.cpp
+++ b/lld/ELF/Symbols.cpp
@@ -331,6 +331,34 @@
report(": unable to order discarded symbol: ");
}
+// Returns true if a symbol can be replaced at load-time by a symbol
+// with the same name defined in other ELF executable or DSO.
+bool computeIsPreemptible(const Symbol &sym) {
+ assert(!sym.isLocal());
+
+ // Only symbols with default visibility that appear in dynsym can be
+ // preempted. Symbols with protected visibility cannot be preempted.
+ if (!sym.includeInDynsym() || sym.visibility != STV_DEFAULT)
+ return false;
+
+ // At this point copy relocations have not been created yet, so any
+ // symbol that is not defined locally is preemptible.
+ if (!sym.isDefined())
+ return true;
+
+ if (!config->shared)
+ return false;
+
+ // If the dynamic list is present, it specifies preemptable symbols in a DSO.
+ if (config->hasDynamicList)
+ return sym.inDynamicList;
+
+ // -Bsymbolic means that definitions are not preempted.
+ if (config->bsymbolic || (config->bsymbolicFunctions && sym.isFunc()))
+ return false;
+ return true;
+}
+
static uint8_t getMinVisibility(uint8_t va, uint8_t vb) {
if (va == STV_DEFAULT)
return vb;
