Currently, building DPDK with clang + LTO is unsupported, which is a
showstopper for cross-language interprocedural optimizations. The root
cause is that pmdinfogen expects to scan through the section headers of
generated ELF object files, but clang's "-flto" flag generates LLVM
bitcode instead. This patch enables LTO builds with clang, provided that
the linker is set to lld.
The mechanism of action is clang's "-fembed-bitcode" flag, which acts
similarly to gcc's "-ffat-lto-objects" - the compiler outputs a normal
ELF object file that keeps pmdinfogen happy, but also embeds IR bitcode
in a special section of the ELF that lld can then use to construct the
final binary.
Signed-off-by: Mahdi Rakhshandehroo <mahdi.rakhshandeh...@gmail.com>
---
Forgot to remove get_linker_id() check from the previous patch - that
function is only available in Meson >= 0.54.
config/meson.build | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/config/meson.build b/config/meson.build
index 7134e80..5425181 100644
--- a/config/meson.build
+++ b/config/meson.build
@@ -406,16 +406,21 @@ if is_windows
endif
if get_option('b_lto')
- if cc.has_argument('-ffat-lto-objects')
+ if cc.get_id() == 'gcc' and cc.has_argument('-ffat-lto-objects')
add_project_arguments('-ffat-lto-objects', language: 'c')
+
+ # workaround for gcc 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
+ elif cc.get_id() == 'clang' and cc.has_argument('-fembed-bitcode')
+ # TODO: enforce use of lld using cc.get_linker_id() with Meson >= 0.54
+ add_project_arguments('-fno-lto', '-fembed-bitcode', language: 'c')
+ endif
else
error('compiler does not support fat LTO objects - please turn LTO
off')
endif
- # workaround for gcc bug 81440
- if cc.get_id() == 'gcc' and 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
if get_option('b_sanitize') == 'address' or get_option('b_sanitize') ==
'address,undefined'
--
2.25.1
