Re: [dpdk-dev] [PATCH v2 01/10] build: add an option to enable LTO build

[Ray Kinsella <mdr@ashroe.eu>]

this is cool, good work.
comments below.

On 17/09/2019 08:57, Andrzej Ostruszka wrote:
> This patch adds an option to enable link time optimization.  In addition
> to LTO option itself (-flto) fat-lto-objects are being used.  This is
> because during the build pmdinfogen scans the generated ELF objects to
> find this_pmd_name* symbol in symbol table.  Without fat-lto-objects gcc
> produces ELF only with extra symbols for internal use during linking and
> clang does not produce ELF at all (only LLVM IR bitcode).
> 
> Signed-off-by: Andrzej Ostruszka <aostruszka@marvell.com>
> ---
>  .travis.yml                                  |  7 ++++
>  config/common_base                           |  5 +++
>  config/meson.build                           | 15 ++++++++
>  doc/guides/prog_guide/lto.rst                | 37 ++++++++++++++++++++
>  doc/guides/rel_notes/release_19_11.rst       |  8 +++++
>  lib/librte_distributor/rte_distributor.c     | 18 +++++-----
>  lib/librte_distributor/rte_distributor_v20.c | 18 +++++-----
>  lib/librte_lpm/rte_lpm.c                     | 28 +++++++--------
>  lib/librte_lpm/rte_lpm6.c                    | 16 ++++-----
>  lib/librte_timer/rte_timer.c                 | 20 +++++------
>  mk/toolchain/clang/rte.toolchain-compat.mk   |  4 +++
>  mk/toolchain/clang/rte.vars.mk               |  8 +++++
>  mk/toolchain/gcc/rte.toolchain-compat.mk     |  4 +++
>  mk/toolchain/gcc/rte.vars.mk                 | 12 +++++++
>  mk/toolchain/icc/rte.vars.mk                 |  8 +++++
>  15 files changed, 158 insertions(+), 50 deletions(-)
>  create mode 100644 doc/guides/prog_guide/lto.rst
> 
> diff --git a/.travis.yml b/.travis.yml
> index 781f9f666..70d221852 100644
> --- a/.travis.yml
> +++ b/.travis.yml
> @@ -31,6 +31,7 @@ env:
>    - DEF_LIB="static" OPTS="-Denable_kmods=false"
>    - DEF_LIB="shared" OPTS="-Denable_kmods=false"
>    - DEF_LIB="shared" RUN_TESTS=1 BUILD_DOCS=1
> +  - DEF_LIB="shared" OPTS="-Db_lto=true"
>  
>  matrix:
>    include:
> @@ -100,6 +101,12 @@ matrix:
>        apt:
>          packages:
>            - *extra_packages
> +  - env: DEF_LIB="shared" OPTS="-Db_lto=true" EXTRA_PACKAGES=1
> +    compiler: gcc
> +    addons:
> +      apt:
> +        packages:
> +          - *extra_packages
>  
>  
>  script: ./.ci/${TRAVIS_OS_NAME}-build.sh
> diff --git a/config/common_base b/config/common_base
> index 8ef75c203..73a55fdec 100644
> --- a/config/common_base
> +++ b/config/common_base
> @@ -49,6 +49,11 @@ CONFIG_RTE_FORCE_INTRINSICS=n
>  #
>  CONFIG_RTE_ARCH_STRICT_ALIGN=n
>  
> +#
> +# Enable link time optimization
> +#
> +CONFIG_RTE_ENABLE_LTO=n
> +
>  #
>  # Compile to share library
>  #

Why would we make this optional in this way and expand the matrix of
different ways to build DPDK. To ask another way, why wouldn't a user
turn on GSO.

> diff --git a/config/meson.build b/config/meson.build
> index 2bafea530..97bbc323b 100644
> --- a/config/meson.build
> +++ b/config/meson.build
> @@ -196,3 +196,18 @@ add_project_arguments('-D_GNU_SOURCE', language: 'c')
>  if is_freebsd
>  	add_project_arguments('-D__BSD_VISIBLE', language: 'c')
>  endif
> +
> +if get_option('b_lto')
> +	if cc.has_argument('-ffat-lto-objects')
> +		add_project_arguments('-ffat-lto-objects', language: 'c')
> +	else
> +		error('compiler does not support fat LTO objects - please turn LTO off')
> +	endif
> +	if cc.get_id() == 'gcc'
> +		# workaround for bug 81440
> +		if cc.version().version_compare('<8.0')
> +			add_project_arguments('-Wno-lto-type-mismatch', language: 'c')
> +			add_project_link_arguments('-Wno-lto-type-mismatch', language: 'c')
> +		endif
> +	endif
> +endif
> diff --git a/doc/guides/prog_guide/lto.rst b/doc/guides/prog_guide/lto.rst
> new file mode 100644
> index 000000000..b2b36e51c
> --- /dev/null
> +++ b/doc/guides/prog_guide/lto.rst
> @@ -0,0 +1,37 @@
> +Link Time Optimization
> +======================
> +
> +The DPDK framework supports compilation with link time optimization
> +turned on.  This depends obviously on the capabilities of the compiler
> +to do "whole program" optimization at link time and is available only
> +for compilers that support that feature (gcc, clang and icc).  To be
> +more specific compiler have to support creation of ELF objects
> +containing both normal code and internal representation
> +(fat-lto-objects).  This is required since during build some code is
> +generated by parsing produced ELF objects (pmdinfogen).
> +
> +The amount of performance gain that one can get from LTO depends on the
> +compiler and the code that is being compiled.  However LTO is also
> +useful for additional code analysis done by the compiler.  In particular
> +due to interprocedural analysis compiler can produce additional warnings
> +about variables that might be used uninitialized.  Some of these
> +warnings might be "false positives" though and you might need to
> +explicitly initialize variable in order to silence the compiler.
> +
> +Link time optimization can be enabled for whole DPDK framework by
> +setting:
> +
> +.. code-block:: console
> +    CONFIG_ENABLE_LTO=y
> +
> +in config file for the case of make based build and by:
> +
> +.. code-block:: console
> +    meson build -Db_lto=true -Ddefault_library=shared
> +    ninja -C build
> +
> +for the case of meson based build (only shared libraries are supported
> +when building with meson and LTO enabled).
> +
> +Please note that turning LTO on causes considerable extension of
> +compilation time.
> diff --git a/doc/guides/rel_notes/release_19_11.rst b/doc/guides/rel_notes/release_19_11.rst
> index 8490d897c..97b4f4083 100644
> --- a/doc/guides/rel_notes/release_19_11.rst
> +++ b/doc/guides/rel_notes/release_19_11.rst
> @@ -56,6 +56,14 @@ New Features
>       Also, make sure to start the actual text at the margin.
>       =========================================================
>  
> +**Added build support for Link Time Optimization.**
> +
> + LTO is an optimization technique used by the compiler to perform whole
> + program analysis and optimization at link time.  In order to do that
> + compilers store their internal representation of the source code that
> + the linker uses at the final stage of compilation process.
> +
> + See :doc:`../prog_guide/lto` for more information:
>  
>  Removed Items
>  -------------
> diff --git a/lib/librte_distributor/rte_distributor.c b/lib/librte_distributor/rte_distributor.c
> index 21eb1fb0a..848250f4a 100644
> --- a/lib/librte_distributor/rte_distributor.c
> +++ b/lib/librte_distributor/rte_distributor.c
> @@ -32,7 +32,7 @@ EAL_REGISTER_TAILQ(rte_dist_burst_tailq)
>  
>  /**** Burst Packet APIs called by workers ****/
>  
> -void
> +void __vsym

all these additional __vsym annotations looks like they belong in a
seperate patch, as they are fixing a bug and are not directly related to
adding LTO the build system.

>  rte_distributor_request_pkt_v1705(struct rte_distributor *d,
>  		unsigned int worker_id, struct rte_mbuf **oldpkt,
>  		unsigned int count)
> @@ -84,7 +84,7 @@ MAP_STATIC_SYMBOL(void rte_distributor_request_pkt(struct rte_distributor *d,
>  		unsigned int count),
>  		rte_distributor_request_pkt_v1705);
>  
> -int
> +int __vsym
>  rte_distributor_poll_pkt_v1705(struct rte_distributor *d,
>  		unsigned int worker_id, struct rte_mbuf **pkts)
>  {
> @@ -124,7 +124,7 @@ MAP_STATIC_SYMBOL(int rte_distributor_poll_pkt(struct rte_distributor *d,
>  		unsigned int worker_id, struct rte_mbuf **pkts),
>  		rte_distributor_poll_pkt_v1705);
>  
> -int
> +int __vsym
>  rte_distributor_get_pkt_v1705(struct rte_distributor *d,
>  		unsigned int worker_id, struct rte_mbuf **pkts,
>  		struct rte_mbuf **oldpkt, unsigned int return_count)
> @@ -159,7 +159,7 @@ MAP_STATIC_SYMBOL(int rte_distributor_get_pkt(struct rte_distributor *d,
>  		struct rte_mbuf **oldpkt, unsigned int return_count),
>  		rte_distributor_get_pkt_v1705);
>  
> -int
> +int __vsym
>  rte_distributor_return_pkt_v1705(struct rte_distributor *d,
>  		unsigned int worker_id, struct rte_mbuf **oldpkt, int num)
>  {
> @@ -335,7 +335,7 @@ release(struct rte_distributor *d, unsigned int wkr)
>  
>  
>  /* process a set of packets to distribute them to workers */
> -int
> +int __vsym
>  rte_distributor_process_v1705(struct rte_distributor *d,
>  		struct rte_mbuf **mbufs, unsigned int num_mbufs)
>  {
> @@ -476,7 +476,7 @@ MAP_STATIC_SYMBOL(int rte_distributor_process(struct rte_distributor *d,
>  		rte_distributor_process_v1705);
>  
>  /* return to the caller, packets returned from workers */
> -int
> +int __vsym
>  rte_distributor_returned_pkts_v1705(struct rte_distributor *d,
>  		struct rte_mbuf **mbufs, unsigned int max_mbufs)
>  {
> @@ -526,7 +526,7 @@ total_outstanding(const struct rte_distributor *d)
>   * Flush the distributor, so that there are no outstanding packets in flight or
>   * queued up.
>   */
> -int
> +int __vsym
>  rte_distributor_flush_v1705(struct rte_distributor *d)
>  {
>  	unsigned int flushed;
> @@ -561,7 +561,7 @@ MAP_STATIC_SYMBOL(int rte_distributor_flush(struct rte_distributor *d),
>  		rte_distributor_flush_v1705);
>  
>  /* clears the internal returns array in the distributor */
> -void
> +void __vsym
>  rte_distributor_clear_returns_v1705(struct rte_distributor *d)
>  {
>  	unsigned int wkr;
> @@ -581,7 +581,7 @@ MAP_STATIC_SYMBOL(void rte_distributor_clear_returns(struct rte_distributor *d),
>  		rte_distributor_clear_returns_v1705);
>  
>  /* creates a distributor instance */
> -struct rte_distributor *
> +struct rte_distributor * __vsym
>  rte_distributor_create_v1705(const char *name,
>  		unsigned int socket_id,
>  		unsigned int num_workers,
> diff --git a/lib/librte_distributor/rte_distributor_v20.c b/lib/librte_distributor/rte_distributor_v20.c
> index cdc0969a8..31c766421 100644
> --- a/lib/librte_distributor/rte_distributor_v20.c
> +++ b/lib/librte_distributor/rte_distributor_v20.c
> @@ -27,7 +27,7 @@ EAL_REGISTER_TAILQ(rte_distributor_tailq)
>  
>  /**** APIs called by workers ****/
>  
> -void
> +void __vsym
>  rte_distributor_request_pkt_v20(struct rte_distributor_v20 *d,
>  		unsigned worker_id, struct rte_mbuf *oldpkt)
>  {
> @@ -40,7 +40,7 @@ rte_distributor_request_pkt_v20(struct rte_distributor_v20 *d,
>  }
>  VERSION_SYMBOL(rte_distributor_request_pkt, _v20, 2.0);
>  
> -struct rte_mbuf *
> +struct rte_mbuf * __vsym
>  rte_distributor_poll_pkt_v20(struct rte_distributor_v20 *d,
>  		unsigned worker_id)
>  {
> @@ -54,7 +54,7 @@ rte_distributor_poll_pkt_v20(struct rte_distributor_v20 *d,
>  }
>  VERSION_SYMBOL(rte_distributor_poll_pkt, _v20, 2.0);
>  
> -struct rte_mbuf *
> +struct rte_mbuf * __vsym
>  rte_distributor_get_pkt_v20(struct rte_distributor_v20 *d,
>  		unsigned worker_id, struct rte_mbuf *oldpkt)
>  {
> @@ -66,7 +66,7 @@ rte_distributor_get_pkt_v20(struct rte_distributor_v20 *d,
>  }
>  VERSION_SYMBOL(rte_distributor_get_pkt, _v20, 2.0);
>  
> -int
> +int __vsym
>  rte_distributor_return_pkt_v20(struct rte_distributor_v20 *d,
>  		unsigned worker_id, struct rte_mbuf *oldpkt)
>  {
> @@ -191,7 +191,7 @@ process_returns(struct rte_distributor_v20 *d)
>  }
>  
>  /* process a set of packets to distribute them to workers */
> -int
> +int __vsym
>  rte_distributor_process_v20(struct rte_distributor_v20 *d,
>  		struct rte_mbuf **mbufs, unsigned num_mbufs)
>  {
> @@ -296,7 +296,7 @@ rte_distributor_process_v20(struct rte_distributor_v20 *d,
>  VERSION_SYMBOL(rte_distributor_process, _v20, 2.0);
>  
>  /* return to the caller, packets returned from workers */
> -int
> +int __vsym
>  rte_distributor_returned_pkts_v20(struct rte_distributor_v20 *d,
>  		struct rte_mbuf **mbufs, unsigned max_mbufs)
>  {
> @@ -334,7 +334,7 @@ total_outstanding(const struct rte_distributor_v20 *d)
>  
>  /* flush the distributor, so that there are no outstanding packets in flight or
>   * queued up. */
> -int
> +int __vsym
>  rte_distributor_flush_v20(struct rte_distributor_v20 *d)
>  {
>  	const unsigned flushed = total_outstanding(d);
> @@ -347,7 +347,7 @@ rte_distributor_flush_v20(struct rte_distributor_v20 *d)
>  VERSION_SYMBOL(rte_distributor_flush, _v20, 2.0);
>  
>  /* clears the internal returns array in the distributor */
> -void
> +void __vsym
>  rte_distributor_clear_returns_v20(struct rte_distributor_v20 *d)
>  {
>  	d->returns.start = d->returns.count = 0;
> @@ -358,7 +358,7 @@ rte_distributor_clear_returns_v20(struct rte_distributor_v20 *d)
>  VERSION_SYMBOL(rte_distributor_clear_returns, _v20, 2.0);
>  
>  /* creates a distributor instance */
> -struct rte_distributor_v20 *
> +struct rte_distributor_v20 * __vsym
>  rte_distributor_create_v20(const char *name,
>  		unsigned socket_id,
>  		unsigned num_workers)
> diff --git a/lib/librte_lpm/rte_lpm.c b/lib/librte_lpm/rte_lpm.c
> index 3a929a1b1..a2fba8d61 100644
> --- a/lib/librte_lpm/rte_lpm.c
> +++ b/lib/librte_lpm/rte_lpm.c
> @@ -89,7 +89,7 @@ depth_to_range(uint8_t depth)
>  /*
>   * Find an existing lpm table and return a pointer to it.
>   */
> -struct rte_lpm_v20 *
> +struct rte_lpm_v20 * __vsym
>  rte_lpm_find_existing_v20(const char *name)
>  {
>  	struct rte_lpm_v20 *l = NULL;
> @@ -115,7 +115,7 @@ rte_lpm_find_existing_v20(const char *name)
>  }
>  VERSION_SYMBOL(rte_lpm_find_existing, _v20, 2.0);
>  
> -struct rte_lpm *
> +struct rte_lpm * __vsym
>  rte_lpm_find_existing_v1604(const char *name)
>  {
>  	struct rte_lpm *l = NULL;
> @@ -146,7 +146,7 @@ MAP_STATIC_SYMBOL(struct rte_lpm *rte_lpm_find_existing(const char *name),
>  /*
>   * Allocates memory for LPM object
>   */
> -struct rte_lpm_v20 *
> +struct rte_lpm_v20 * __vsym
>  rte_lpm_create_v20(const char *name, int socket_id, int max_rules,
>  		__rte_unused int flags)
>  {
> @@ -219,7 +219,7 @@ rte_lpm_create_v20(const char *name, int socket_id, int max_rules,
>  }
>  VERSION_SYMBOL(rte_lpm_create, _v20, 2.0);
>  
> -struct rte_lpm *
> +struct rte_lpm * __vsym
>  rte_lpm_create_v1604(const char *name, int socket_id,
>  		const struct rte_lpm_config *config)
>  {
> @@ -328,7 +328,7 @@ MAP_STATIC_SYMBOL(
>  /*
>   * Deallocates memory for given LPM table.
>   */
> -void
> +void __vsym
>  rte_lpm_free_v20(struct rte_lpm_v20 *lpm)
>  {
>  	struct rte_lpm_list *lpm_list;
> @@ -357,7 +357,7 @@ rte_lpm_free_v20(struct rte_lpm_v20 *lpm)
>  }
>  VERSION_SYMBOL(rte_lpm_free, _v20, 2.0);
>  
> -void
> +void __vsym
>  rte_lpm_free_v1604(struct rte_lpm *lpm)
>  {
>  	struct rte_lpm_list *lpm_list;
> @@ -1176,7 +1176,7 @@ add_depth_big_v1604(struct rte_lpm *lpm, uint32_t ip_masked, uint8_t depth,
>  /*
>   * Add a route
>   */
> -int
> +int __vsym
>  rte_lpm_add_v20(struct rte_lpm_v20 *lpm, uint32_t ip, uint8_t depth,
>  		uint8_t next_hop)
>  {
> @@ -1217,7 +1217,7 @@ rte_lpm_add_v20(struct rte_lpm_v20 *lpm, uint32_t ip, uint8_t depth,
>  }
>  VERSION_SYMBOL(rte_lpm_add, _v20, 2.0);
>  
> -int
> +int __vsym
>  rte_lpm_add_v1604(struct rte_lpm *lpm, uint32_t ip, uint8_t depth,
>  		uint32_t next_hop)
>  {
> @@ -1263,7 +1263,7 @@ MAP_STATIC_SYMBOL(int rte_lpm_add(struct rte_lpm *lpm, uint32_t ip,
>  /*
>   * Look for a rule in the high-level rules table
>   */
> -int
> +int __vsym
>  rte_lpm_is_rule_present_v20(struct rte_lpm_v20 *lpm, uint32_t ip, uint8_t depth,
>  uint8_t *next_hop)
>  {
> @@ -1290,7 +1290,7 @@ uint8_t *next_hop)
>  }
>  VERSION_SYMBOL(rte_lpm_is_rule_present, _v20, 2.0);
>  
> -int
> +int __vsym
>  rte_lpm_is_rule_present_v1604(struct rte_lpm *lpm, uint32_t ip, uint8_t depth,
>  uint32_t *next_hop)
>  {
> @@ -1843,7 +1843,7 @@ delete_depth_big_v1604(struct rte_lpm *lpm, uint32_t ip_masked,
>  /*
>   * Deletes a rule
>   */
> -int
> +int __vsym
>  rte_lpm_delete_v20(struct rte_lpm_v20 *lpm, uint32_t ip, uint8_t depth)
>  {
>  	int32_t rule_to_delete_index, sub_rule_index;
> @@ -1897,7 +1897,7 @@ rte_lpm_delete_v20(struct rte_lpm_v20 *lpm, uint32_t ip, uint8_t depth)
>  }
>  VERSION_SYMBOL(rte_lpm_delete, _v20, 2.0);
>  
> -int
> +int __vsym
>  rte_lpm_delete_v1604(struct rte_lpm *lpm, uint32_t ip, uint8_t depth)
>  {
>  	int32_t rule_to_delete_index, sub_rule_index;
> @@ -1956,7 +1956,7 @@ MAP_STATIC_SYMBOL(int rte_lpm_delete(struct rte_lpm *lpm, uint32_t ip,
>  /*
>   * Delete all rules from the LPM table.
>   */
> -void
> +void __vsym
>  rte_lpm_delete_all_v20(struct rte_lpm_v20 *lpm)
>  {
>  	/* Zero rule information. */
> @@ -1973,7 +1973,7 @@ rte_lpm_delete_all_v20(struct rte_lpm_v20 *lpm)
>  }
>  VERSION_SYMBOL(rte_lpm_delete_all, _v20, 2.0);
>  
> -void
> +void __vsym
>  rte_lpm_delete_all_v1604(struct rte_lpm *lpm)
>  {
>  	/* Zero rule information. */
> diff --git a/lib/librte_lpm/rte_lpm6.c b/lib/librte_lpm/rte_lpm6.c
> index 9b8aeb972..49a7fea1d 100644
> --- a/lib/librte_lpm/rte_lpm6.c
> +++ b/lib/librte_lpm/rte_lpm6.c
> @@ -811,7 +811,7 @@ add_step(struct rte_lpm6 *lpm, struct rte_lpm6_tbl_entry *tbl,
>  /*
>   * Add a route
>   */
> -int
> +int __vsym
>  rte_lpm6_add_v20(struct rte_lpm6 *lpm, uint8_t *ip, uint8_t depth,
>  		uint8_t next_hop)
>  {
> @@ -861,7 +861,7 @@ simulate_add(struct rte_lpm6 *lpm, const uint8_t *masked_ip, uint8_t depth)
>  	return 0;
>  }
>  
> -int
> +int __vsym
>  rte_lpm6_add_v1705(struct rte_lpm6 *lpm, uint8_t *ip, uint8_t depth,
>  		uint32_t next_hop)
>  {
> @@ -954,7 +954,7 @@ lookup_step(const struct rte_lpm6 *lpm, const struct rte_lpm6_tbl_entry *tbl,
>  /*
>   * Looks up an IP
>   */
> -int
> +int __vsym
>  rte_lpm6_lookup_v20(const struct rte_lpm6 *lpm, uint8_t *ip, uint8_t *next_hop)
>  {
>  	uint32_t next_hop32 = 0;
> @@ -972,7 +972,7 @@ rte_lpm6_lookup_v20(const struct rte_lpm6 *lpm, uint8_t *ip, uint8_t *next_hop)
>  }
>  VERSION_SYMBOL(rte_lpm6_lookup, _v20, 2.0);
>  
> -int
> +int __vsym
>  rte_lpm6_lookup_v1705(const struct rte_lpm6 *lpm, uint8_t *ip,
>  		uint32_t *next_hop)
>  {
> @@ -1007,7 +1007,7 @@ MAP_STATIC_SYMBOL(int rte_lpm6_lookup(const struct rte_lpm6 *lpm, uint8_t *ip,
>  /*
>   * Looks up a group of IP addresses
>   */
> -int
> +int __vsym
>  rte_lpm6_lookup_bulk_func_v20(const struct rte_lpm6 *lpm,
>  		uint8_t ips[][RTE_LPM6_IPV6_ADDR_SIZE],
>  		int16_t * next_hops, unsigned n)
> @@ -1048,7 +1048,7 @@ rte_lpm6_lookup_bulk_func_v20(const struct rte_lpm6 *lpm,
>  }
>  VERSION_SYMBOL(rte_lpm6_lookup_bulk_func, _v20, 2.0);
>  
> -int
> +int __vsym
>  rte_lpm6_lookup_bulk_func_v1705(const struct rte_lpm6 *lpm,
>  		uint8_t ips[][RTE_LPM6_IPV6_ADDR_SIZE],
>  		int32_t *next_hops, unsigned int n)
> @@ -1098,7 +1098,7 @@ MAP_STATIC_SYMBOL(int rte_lpm6_lookup_bulk_func(const struct rte_lpm6 *lpm,
>  /*
>   * Look for a rule in the high-level rules table
>   */
> -int
> +int __vsym
>  rte_lpm6_is_rule_present_v20(struct rte_lpm6 *lpm, uint8_t *ip, uint8_t depth,
>  		uint8_t *next_hop)
>  {
> @@ -1118,7 +1118,7 @@ rte_lpm6_is_rule_present_v20(struct rte_lpm6 *lpm, uint8_t *ip, uint8_t depth,
>  }
>  VERSION_SYMBOL(rte_lpm6_is_rule_present, _v20, 2.0);
>  
> -int
> +int __vsym
>  rte_lpm6_is_rule_present_v1705(struct rte_lpm6 *lpm, uint8_t *ip, uint8_t depth,
>  		uint32_t *next_hop)
>  {
> diff --git a/lib/librte_timer/rte_timer.c b/lib/librte_timer/rte_timer.c
> index bdcf05d06..e560ace06 100644
> --- a/lib/librte_timer/rte_timer.c
> +++ b/lib/librte_timer/rte_timer.c
> @@ -131,7 +131,7 @@ rte_timer_data_dealloc(uint32_t id)
>  	return 0;
>  }
>  
> -void
> +void __vsym
>  rte_timer_subsystem_init_v20(void)
>  {
>  	unsigned lcore_id;
> @@ -153,7 +153,7 @@ VERSION_SYMBOL(rte_timer_subsystem_init, _v20, 2.0);
>   * secondary processes should be empty, the zeroth entry can be shared by
>   * multiple processes.
>   */
> -int
> +int __vsym
>  rte_timer_subsystem_init_v1905(void)
>  {
>  	const struct rte_memzone *mz;
> @@ -551,7 +551,7 @@ __rte_timer_reset(struct rte_timer *tim, uint64_t expire,
>  }
>  
>  /* Reset and start the timer associated with the timer handle tim */
> -int
> +int __vsym
>  rte_timer_reset_v20(struct rte_timer *tim, uint64_t ticks,
>  		    enum rte_timer_type type, unsigned int tim_lcore,
>  		    rte_timer_cb_t fct, void *arg)
> @@ -574,7 +574,7 @@ rte_timer_reset_v20(struct rte_timer *tim, uint64_t ticks,
>  }
>  VERSION_SYMBOL(rte_timer_reset, _v20, 2.0);
>  
> -int
> +int __vsym
>  rte_timer_reset_v1905(struct rte_timer *tim, uint64_t ticks,
>  		      enum rte_timer_type type, unsigned int tim_lcore,
>  		      rte_timer_cb_t fct, void *arg)
> @@ -657,14 +657,14 @@ __rte_timer_stop(struct rte_timer *tim, int local_is_locked,
>  }
>  
>  /* Stop the timer associated with the timer handle tim */
> -int
> +int __vsym
>  rte_timer_stop_v20(struct rte_timer *tim)
>  {
>  	return __rte_timer_stop(tim, 0, &default_timer_data);
>  }
>  VERSION_SYMBOL(rte_timer_stop, _v20, 2.0);
>  
> -int
> +int __vsym
>  rte_timer_stop_v1905(struct rte_timer *tim)
>  {
>  	return rte_timer_alt_stop(default_data_id, tim);
> @@ -817,14 +817,14 @@ __rte_timer_manage(struct rte_timer_data *timer_data)
>  	priv_timer[lcore_id].running_tim = NULL;
>  }
>  
> -void
> +void __vsym
>  rte_timer_manage_v20(void)
>  {
>  	__rte_timer_manage(&default_timer_data);
>  }
>  VERSION_SYMBOL(rte_timer_manage, _v20, 2.0);
>  
> -int
> +int __vsym
>  rte_timer_manage_v1905(void)
>  {
>  	struct rte_timer_data *timer_data;
> @@ -1074,14 +1074,14 @@ __rte_timer_dump_stats(struct rte_timer_data *timer_data __rte_unused, FILE *f)
>  #endif
>  }
>  
> -void
> +void __vsym
>  rte_timer_dump_stats_v20(FILE *f)
>  {
>  	__rte_timer_dump_stats(&default_timer_data, f);
>  }
>  VERSION_SYMBOL(rte_timer_dump_stats, _v20, 2.0);
>  
> -int
> +int __vsym
>  rte_timer_dump_stats_v1905(FILE *f)
>  {
>  	return rte_timer_alt_dump_stats(default_data_id, f);
> diff --git a/mk/toolchain/clang/rte.toolchain-compat.mk b/mk/toolchain/clang/rte.toolchain-compat.mk
> index e6189b498..78f96c648 100644
> --- a/mk/toolchain/clang/rte.toolchain-compat.mk
> +++ b/mk/toolchain/clang/rte.toolchain-compat.mk
> @@ -20,3 +20,7 @@ CLANG_MINOR_VERSION := $(shell echo $(CLANG_VERSION) | cut -f2 -d.)
>  ifeq ($(shell test $(CLANG_MAJOR_VERSION)$(CLANG_MINOR_VERSION) -lt 35 && echo 1), 1)
>  	CC_SUPPORTS_Z := false
>  endif
> +
> +ifeq ($(shell test $(CLANG_MAJOR_VERSION)$(CLANG_MINOR_VERSION) -lt 60 && echo 1), 1)
> +	CONFIG_RTE_ENABLE_LTO=n
> +endif
> diff --git a/mk/toolchain/clang/rte.vars.mk b/mk/toolchain/clang/rte.vars.mk
> index 3c49dc568..3b1fa05f9 100644
> --- a/mk/toolchain/clang/rte.vars.mk
> +++ b/mk/toolchain/clang/rte.vars.mk
> @@ -48,6 +48,14 @@ endif
>  # process cpu flags
>  include $(RTE_SDK)/mk/toolchain/$(RTE_TOOLCHAIN)/rte.toolchain-compat.mk
>  
> +ifeq ($(CONFIG_RTE_ENABLE_LTO),y)
> +# 'fat-lto' is used since pmdinfogen needs to have 'this_pmd_nameX'
> +# exported in symbol table and without this option only internal
> +# representation is present.
> +TOOLCHAIN_CFLAGS += -flto -ffat-lto-objects
> +TOOLCHAIN_LDFLAGS += -flto
> +endif
> +
>  # workaround clang bug with warning "missing field initializer" for "= {0}"
>  WERROR_FLAGS += -Wno-missing-field-initializers
>  
> diff --git a/mk/toolchain/gcc/rte.toolchain-compat.mk b/mk/toolchain/gcc/rte.toolchain-compat.mk
> index ea40a11c0..ad4fad83c 100644
> --- a/mk/toolchain/gcc/rte.toolchain-compat.mk
> +++ b/mk/toolchain/gcc/rte.toolchain-compat.mk
> @@ -88,6 +88,10 @@ else
>  		MACHINE_CFLAGS := $(filter-out -march% -mtune% -msse%,$(MACHINE_CFLAGS))
>  	endif
>  
> +	ifeq ($(shell test $(GCC_VERSION) -lt 45 && echo 1), 1)
> +		CONFIG_RTE_ENABLE_LTO=n
> +	endif
> +
>  	# Disable thunderx PMD for gcc < 4.7
>  	ifeq ($(shell test $(GCC_VERSION) -lt 47 && echo 1), 1)
>  		CONFIG_RTE_LIBRTE_THUNDERX_NICVF_PMD=d
> diff --git a/mk/toolchain/gcc/rte.vars.mk b/mk/toolchain/gcc/rte.vars.mk
> index b852fcfd7..9fc704193 100644
> --- a/mk/toolchain/gcc/rte.vars.mk
> +++ b/mk/toolchain/gcc/rte.vars.mk
> @@ -62,6 +62,18 @@ endif
>  # process cpu flags
>  include $(RTE_SDK)/mk/toolchain/$(RTE_TOOLCHAIN)/rte.toolchain-compat.mk
>  
> +ifeq ($(CONFIG_RTE_ENABLE_LTO),y)
> +# 'fat-lto' is used since pmdinfogen needs to have 'this_pmd_nameX'
> +# exported in symbol table and without this option only internal
> +# representation is present.
> +TOOLCHAIN_CFLAGS += -flto -ffat-lto-objects
> +TOOLCHAIN_LDFLAGS += -flto
> +# workaround for GCC bug 81440
> +ifeq ($(shell test $(GCC_VERSION) -lt 80 && echo 1), 1)
> +WERROR_FLAGS += -Wno-lto-type-mismatch
> +endif
> +endif
> +
>  # workaround GCC bug with warning "missing initializer" for "= {0}"
>  ifeq ($(shell test $(GCC_VERSION) -lt 47 && echo 1), 1)
>  WERROR_FLAGS += -Wno-missing-field-initializers
> diff --git a/mk/toolchain/icc/rte.vars.mk b/mk/toolchain/icc/rte.vars.mk
> index aa1422bf1..8aa87aa1e 100644
> --- a/mk/toolchain/icc/rte.vars.mk
> +++ b/mk/toolchain/icc/rte.vars.mk
> @@ -54,5 +54,13 @@ endif
>  # process cpu flags
>  include $(RTE_SDK)/mk/toolchain/$(RTE_TOOLCHAIN)/rte.toolchain-compat.mk
>  
> +ifeq ($(CONFIG_RTE_ENABLE_LTO),y)
> +# 'fat-lto' is used since pmdinfogen needs to have 'this_pmd_nameX'
> +# exported in symbol table and without this option only internal
> +# representation is present.
> +TOOLCHAIN_CFLAGS += -flto -ffat-lto-objects
> +TOOLCHAIN_LDFLAGS += -flto
> +endif
> +
>  export CC AS AR LD OBJCOPY OBJDUMP STRIP READELF
>  export TOOLCHAIN_CFLAGS TOOLCHAIN_LDFLAGS TOOLCHAIN_ASFLAGS
>