Message ID | 20200411221646.185882-1-maskray@google.com |
---|---|
State | New |
Headers | show |
Series | elf: Replace a --defsym trick with an object file to be compatible with lld | expand |
On Sat, Apr 11, 2020 at 3:16 PM Fangrui Song <maskray@google.com> wrote: > > 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. > --- > elf/Makefile | 11 ++++------- > 1 file changed, 4 insertions(+), 7 deletions(-) > > diff --git a/elf/Makefile b/elf/Makefile > index 9b1d58c7ad..de5dff649d 100644 > --- a/elf/Makefile > +++ b/elf/Makefile > @@ -497,10 +497,6 @@ 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. > @@ -509,9 +505,10 @@ 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 $@.o > + echo '$(patsubst %,.globl %;,$(rtld-stubbed-symbols)) $(patsubst %,%:,$(rtld-stubbed-symbols))' | \ > + $(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 $@ > > $(objpfx)librtld.mk: $(objpfx)librtld.map Makefile > -- > 2.26.0.110.g2183baf09c-goog > Ping
diff --git a/elf/Makefile b/elf/Makefile index 9b1d58c7ad..de5dff649d 100644 --- a/elf/Makefile +++ b/elf/Makefile @@ -497,10 +497,6 @@ 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. @@ -509,9 +505,10 @@ 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 $@.o + echo '$(patsubst %,.globl %;,$(rtld-stubbed-symbols)) $(patsubst %,%:,$(rtld-stubbed-symbols))' | \ + $(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 $@ $(objpfx)librtld.mk: $(objpfx)librtld.map Makefile