[PATCH v2] eal: fix function versioning with LTO

[Stephen Hemminger <stephen@networkplumber.org>]

When using function versioning and building with LTO,
GCC gets confused by the symbol versioning using __asm__.
There are no uses of function versioning in upstream repo.
This was found when adding additional parameter to
rte_eth_dev_get_name_by_port.

Assembler messages:
Error: invalid attempt to declare external version name as default in symbol `rte_eth_dev_get_name_by_port@@DPDK_27'

The workaround GCC 10 introduced was an additional function attribute;
clang doesn't have or need this attribute. No need to backport this to
LTS since there is no function versioning in those releases.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
v2 - reword commit message


 lib/eal/common/eal_export.h | 46 +++++++++++++++++++++++++++----------
 1 file changed, 34 insertions(+), 12 deletions(-)

diff --git a/lib/eal/common/eal_export.h b/lib/eal/common/eal_export.h
index 7e47d34064..1318e6278d 100644
--- a/lib/eal/common/eal_export.h
+++ b/lib/eal/common/eal_export.h
@@ -30,39 +30,61 @@
  * new functionality, behavior, etc.  When that occurs, it is desirable to
  * allow for backwards compatibility for a time with older binaries that are
  * dynamically linked to the dpdk.
+ *
+ * RTE_VERSION_SYMBOL
+ * Create a symbol version table entry binding symbol <name>@DPDK_<ver> to the internal
+ * function name <name>_v<ver>.
+ *
+ * RTE_VERSION_EXPERIMENTAL_SYMBOL similar to RTE_VERSION_SYMBOL but for experimental API symbols.
+ * This is mainly used for keeping compatibility for symbols that get promoted to stable ABI.
+ *
+ * RTE_DEFAULT_SYMBOL
+ * Create a symbol version entry instructing the linker to bind references to
+ * symbol <name> to the internal symbol <name>_v<ver>.
  */
 
 #ifdef RTE_BUILD_SHARED_LIB
 
-/*
- * Create a symbol version table entry binding symbol <name>@DPDK_<ver> to the internal
- * function name <name>_v<ver>.
- */
+/* Prefer the compiler method of versioning which uses attributes */
+#if  __has_attribute(symver)
+
+#define RTE_VERSION_SYMBOL(ver, type, name, args) VERSIONING_WARN	\
+	__attribute__((__symver__(RTE_STR(name) "@DPDK_" RTE_STR(ver)))) \
+	type name ## _v ## ver args;					\
+	type name ## _v ## ver args
+
+#define RTE_VERSION_EXPERIMENTAL_SYMBOL(type, name, args) VERSIONING_WARN \
+	__attribute__((__symver__(RTE_STR(name) "@EXPERIMENTAL")))	\
+	type name ## _exp args;						\
+	type name ## _exp args
+
+#define RTE_DEFAULT_SYMBOL(ver, type, name, args) VERSIONING_WARN	\
+	__attribute__((__symver__(RTE_STR(name) "@@DPDK_" RTE_STR(ver)))) \
+	type name ## _v ## ver args;					\
+	type name ## _v ## ver args
+#else /* !__has_attribute(symver) */
+
+/* Use asm tag to create symbol table entry */
 #define RTE_VERSION_SYMBOL(ver, type, name, args) VERSIONING_WARN \
 __asm__(".symver " RTE_STR(name) "_v" RTE_STR(ver) ", " RTE_STR(name) "@DPDK_" RTE_STR(ver)); \
 __rte_used type name ## _v ## ver args; \
 type name ## _v ## ver args
 
-/*
- * Similar to RTE_VERSION_SYMBOL but for experimental API symbols.
- * This is mainly used for keeping compatibility for symbols that get promoted to stable ABI.
- */
 #define RTE_VERSION_EXPERIMENTAL_SYMBOL(type, name, args) VERSIONING_WARN \
 __asm__(".symver " RTE_STR(name) "_exp, " RTE_STR(name) "@EXPERIMENTAL") \
 __rte_used type name ## _exp args; \
 type name ## _exp args
 
-/*
- * Create a symbol version entry instructing the linker to bind references to
- * symbol <name> to the internal symbol <name>_v<ver>.
- */
 #define RTE_DEFAULT_SYMBOL(ver, type, name, args) VERSIONING_WARN \
 __asm__(".symver " RTE_STR(name) "_v" RTE_STR(ver) ", " RTE_STR(name) "@@DPDK_" RTE_STR(ver)); \
 __rte_used type name ## _v ## ver args; \
 type name ## _v ## ver args
 
+#endif /* __has_attribute(symver) */
+
 #else /* !RTE_BUILD_SHARED_LIB */
 
+/* static library does not have versioned symbols */
 #define RTE_VERSION_SYMBOL(ver, type, name, args) VERSIONING_WARN \
 type name ## _v ## ver args; \
 type name ## _v ## ver args
-- 
2.53.0