Re: [dpdk-stable] [seastar-dev] [PATCH] mk: avoid combining -r and -export-dynamic linker options

[Avi Kivity <avi@scylladb.com>]

On 27/01/2020 03.33, Rafael Ávila de Espíndola wrote:
> Running ld with -r switches the linker to a very special mode where
> some other linker options don't make sense.
>
> In particular, -export-dynamic normally requires that all global
> symbols be included in the dynamic symbol table, but a .o file doesn't
> even have a dynamic symbol table.
>
> When given both options it looks like the gnu linker just ignores
> -export-dynamic.
>
> Unfortunately some versions of lld (https://lld.llvm.org/) have a bug
> that causes it to try to create a dynamic symbol table in the output
> .o file and ends up corrupting it
> (https://bugs.llvm.org/show_bug.cgi?id=43552). Current (git) version
> of lld now issues an error.
>
> This patch filters out -export-dynamic from $(LDFLAGS) when using
> -r. With this patch I can build dpdk with lld.
>
> Fixes: 3d781ca32874 ("mk: do post processing on objects that register a driver")
> Cc: stable@dpdk.org
>
> Signed-off-by: Rafael Ávila de Espíndola <espindola@scylladb.com>
> (cherry picked from commit 5a352a3a98e3297555cb08d2db6e45a93ce7e058)
> ---
> Once seastar is updated to use this it should be possible to build
> seastar and scylla with lld, which might help with the bots running
> out of resources during the link.


That turned out to be a configuration problem (docker was limited to a 
small number of tasks, and multithreaded linking overflowed it).


Not to say we shouldn't support lld, of course.


>   mk/internal/rte.compile-pre.mk | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mk/internal/rte.compile-pre.mk b/mk/internal/rte.compile-pre.mk
> index 0cf3791b4..82fe098f7 100644
> --- a/mk/internal/rte.compile-pre.mk
> +++ b/mk/internal/rte.compile-pre.mk
> @@ -61,7 +61,7 @@ CHECK_EXPERIMENTAL = $(EXPERIMENTAL_CHECK) $(SRCDIR)/$(EXPORT_MAP) $@
>   
>   PMDINFO_GEN = $(RTE_SDK_BIN)/app/dpdk-pmdinfogen $@ $@.pmd.c
>   PMDINFO_CC = $(CC) $(CPPFLAGS) $(CFLAGS) $(EXTRA_CFLAGS) -c -o $@.pmd.o $@.pmd.c
> -PMDINFO_LD = $(CROSS)ld $(LDFLAGS) -r -o $@.o $@.pmd.o $@
> +PMDINFO_LD = $(CROSS)ld -r $(filter-out -export-dynamic,$(LDFLAGS)) -o $@.o $@.pmd.o $@
>   PMDINFO_TO_O = if grep -q 'RTE_PMD_REGISTER_.*(.*)' $<; then \
>   	echo "$(if $V,$(PMDINFO_GEN),  PMDINFO $@.pmd.c)" && \
>   	$(PMDINFO_GEN) && \