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From: Fangrui Song <maskray@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc/maskray/lld] elf: Replace a --defsym trick with an object file to be compatible with LLD Date: Mon, 1 Feb 2021 18:01:09 +0000 (GMT) [thread overview] Message-ID: <20210201180109.3D9E73945C06@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=02d393f2483aedc4ce74e6edf8a15f063198041d commit 02d393f2483aedc4ce74e6edf8a15f063198041d Author: Fangrui Song <maskray@google.com> Date: Mon Feb 1 09:29:26 2021 -0800 elf: Replace a --defsym trick with an object file to be compatible with LLD The existing code specifies -Wl,--defsym=malloc=0 and other malloc.os definitions before libc_pic.a so that libc_pic.a(malloc.os) is not fetched. This trick is used to avoid multiple definition errors which would happen as a chain result: dl-allobjs.os has an undefined __libc_scratch_buffer_set_array_size __libc_scratch_buffer_set_array_size fetches libc_pic.a(scratch_buffer_set_array_size.os) libc_pic.a(scratch_buffer_set_array_size.os) has an undefined free free fetches libc_pic.a(malloc.os) libc_pic.a(malloc.os) has an undefined __libc_message __libc_message fetches libc_pic.a(libc_fatal.os) libc_fatal.os will cause a multiple definition error (__GI___libc_fatal) >>> defined at dl-fxstatat64.c >>> /tmp/p/glibc/Release/elf/dl-allobjs.os:(__GI___libc_fatal) >>> defined at libc_fatal.c >>> libc_fatal.os:(.text+0x240) in archive /tmp/p/glibc/Release/libc_pic.a LLD processes --defsym after all input files, so this trick does not suppress multiple definition errors with LLD. Split the step into two and use an object file to make the intention more obvious and make LLD work. This is conceptually more appropriate because --defsym defines a SHN_ABS symbol while a normal definition is relative to the image base. See https://sourceware.org/pipermail/libc-alpha/2020-March/111910.html for discussions about the --defsym semantics. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> Reviewed-by: H.J. Lu <hjl.tools@gmail.com> Diff: --- elf/Makefile | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/elf/Makefile b/elf/Makefile index 5d666b1b0c..16c89b6d07 100644 --- a/elf/Makefile +++ b/elf/Makefile @@ -526,10 +526,6 @@ rtld-stubbed-symbols = \ malloc \ realloc \ -# The GCC arguments that implement $(rtld-stubbed-symbols). -rtld-stubbed-symbols-args = \ - $(patsubst %,-Wl$(comma)--defsym=%=0, $(rtld-stubbed-symbols)) - ifeq ($(have-ssp),yes) # rtld is not built with the stack protector, so these references will # go away in the rebuilds. @@ -538,9 +534,12 @@ endif $(objpfx)librtld.map: $(objpfx)dl-allobjs.os $(common-objpfx)libc_pic.a @-rm -f $@T - $(reloc-link) -o $@.o $(rtld-stubbed-symbols-args) \ - '-Wl,-(' $^ -lgcc '-Wl,-)' -Wl,-Map,$@T - rm -f $@.o + for symbol in $(rtld-stubbed-symbols); do \ + echo ".globl $$symbol"; \ + echo "$$symbol:"; \ + done | $(CC) -o $@T.o $(ASFLAGS) -c -x assembler - + $(reloc-link) -o $@.o $@T.o '-Wl,-(' $^ -lgcc '-Wl,-)' -Wl,-Map,$@T + rm -f %@T.o $@.o mv -f $@T $@ # For lld, skip preceding addresses and values before matching the archive and the member.
next reply other threads:[~2021-02-01 18:01 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-02-01 18:01 Fangrui Song [this message] -- strict thread matches above, loose matches on Subject: below -- 2021-02-01 17:23 Fangrui Song 2021-01-29 18:30 Fangrui Song 2021-01-18 21:41 [glibc/maskray/lld] elf: Replace a --defsym trick with an object file to be compatible with lld Fangrui Song 2021-01-18 21:38 Fangrui Song 2020-12-28 21:08 Fangrui Song 2020-12-28 21:06 Fangrui Song 2020-12-28 19:07 Fangrui Song
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