Re: [PATCH] Makerules: Generate shlib.lds with -fuse-ld=bfd

[Fangrui Song <maskray@google.com>]

On 2022-11-08, Sam James wrote:
>
>
>> On 7 Nov 2022, at 08:31, Florian Weimer via Libc-alpha <libc-alpha@sourceware.org> wrote:
>>
>> * Fangrui Song:
>>
>>> lld does not dump a linker script with --verbose (it does not use a
>>> linker script driven design and lots of linker processing is not
>>> serializable as a linker script anyway).  With the default
>>> --with-default-link=no build, $@T is empty and makes `test -s $@T` fail.
>>>
>>> Just dump the linker script with -fuse-ld=bfd.  lld since 15
>>> (https://reviews.llvm.org/D124656) supports custom RELRO sections in the
>>> GNU ld dumped linker script.
>>> ---
>>> Makerules | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/Makerules b/Makerules
>>> index 09c0cf8357..2edc6ee4e1 100644
>>> --- a/Makerules
>>> +++ b/Makerules
>>> @@ -553,7 +553,7 @@ else
>>> # not for shared objects
>>> $(common-objpfx)shlib.lds: $(common-objpfx)config.make $(..)Makerules
>>> $(LINK.o) -shared -Wl,-O1 \
>>> -   -nostdlib -nostartfiles \
>>> +   -nostdlib -nostartfiles -fuse-ld=bfd \
>>>   $(sysdep-LDFLAGS) $(rtld-LDFLAGS) $(LDFLAGS.so) \
>>>   -Wl,--verbose 2>/dev/null | \
>>>   sed > $@T \
>>
>> Would you please add the comment?
>>
>> I'm not sure if a configure check is required.  We have a path towards
>> removal of the custom linker script; the vfprintf refactor I posted is a
>> first step.
>>
>
>That works for me.
>
>

Added comments...


 From 00ee52ee0753a8d849c23d4e051f10aa8a4e2074 Mon Sep 17 00:00:00 2001
From: Fangrui Song <maskray@google.com>
Date: Mon, 7 Nov 2022 16:21:13 -0800
Subject: [PATCH] Makerules: Generate shlib.lds with -fuse-ld=bfd

lld does not dump a linker script with --verbose (it does not use a
linker script driven design and lots of linker processing is not
serializable as a linker script anyway).  With the default
--with-default-link=no build, $@T is empty and makes `test -s $@T` fail.

Just dump the linker script with -fuse-ld=bfd.  lld since 15
(https://reviews.llvm.org/D124656) supports custom RELRO sections in the
GNU ld dumped linker script.
---
  Makerules | 4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Makerules b/Makerules
index 09c0cf8357..ed6873a1a8 100644
--- a/Makerules
+++ b/Makerules
@@ -546,14 +546,16 @@ endef
  
  ifeq (yes,$(use-default-link))
  # If the linker is good enough, we can let it use its default linker script.
+# In the long term the custom linker script will be removed.
  shlib-lds =
  shlib-lds-flags =
  else
  # binutils only position loadable notes into the first page for binaries,
  # not for shared objects
+# lld --verbose does not dump a linker script.  Use -fuse-ld=bfd.
  $(common-objpfx)shlib.lds: $(common-objpfx)config.make $(..)Makerules
  	$(LINK.o) -shared -Wl,-O1 \
-		  -nostdlib -nostartfiles \
+		  -nostdlib -nostartfiles -fuse-ld=bfd \
  		  $(sysdep-LDFLAGS) $(rtld-LDFLAGS) $(LDFLAGS.so) \
  		  -Wl,--verbose 2>/dev/null | \
  	  sed > $@T \
-- 
2.38.1.431.g37b22c650d-goog