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From: Xi Ruoyao <xry111@xry111.site>
To: binutils@sourceware.org
Cc: liuzhensong@loongson.cn, mengqinggang@loongson.cn,
	i.swmail@xen0n.name, maskray@google.com, hejinyang@loongson.cn,
	cailulu@loongson.cn, Xi Ruoyao <xry111@xry111.site>
Subject: [PATCH] LoongArch: Allow la.got -> la.pcrel relaxation for shared object
Date: Wed,  6 Dec 2023 03:05:47 +0800	[thread overview]
Message-ID: <20231205190547.52950-1-xry111@xry111.site> (raw)

Even in shared objects, la.got -> la.pcrel relaxation can still be
performed for symbols with hidden visibility. For example, if a.c is:

    extern int x;
    int f() { return x++; }

and b.c is:

    int x = 114514;

If compiling and linking with:

    gcc -shared -fPIC -O2 -fvisibility=hidden a.c b.c

Then the la.got in a.o should be relaxed to la.pcrel, and the resulted f
should be like:

    pcaddi  $t0, x
    ldptr.w $a0, $t0, 0
    addi.w  $t1, $a0, 1
    stptr.w $t1, $t0, 0
    ret

Remove bfd_link_executable from the condition of la.got -> la.pcrel
relaxation so this will really happen.  The SYMBOL_REFERENCES_LOCAL
check is enough not to wrongly relax preemptable symbols (for e.g.
when -fvisibility=hidden is not used).

Note that on x86_64 this is also relaxed and the produced code is like:

    lea x(%rip), %rdx
    mov (%rdx), %rax
    lea 1(%rax), %ecx
    mov %ecx, (%rdx)
    ret

Tested by running ld test suite, bootstrapping and regtesting GCC with
the patched ld, and building and testing Glibc with the patched ld.  No
regression is observed.

Signed-off-by: Xi Ruoyao <xry111@xry111.site>
---
 bfd/elfnn-loongarch.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/bfd/elfnn-loongarch.c b/bfd/elfnn-loongarch.c
index 024c5d4cd96..80739b817ab 100644
--- a/bfd/elfnn-loongarch.c
+++ b/bfd/elfnn-loongarch.c
@@ -3986,8 +3986,7 @@ loongarch_elf_relax_section (bfd *abfd, asection *sec,
 	  else
 	    continue;
 
-	  if (h && bfd_link_executable (info)
-	      && SYMBOL_REFERENCES_LOCAL (info, h))
+	  if (h && SYMBOL_REFERENCES_LOCAL (info, h))
 	    local_got = true;
 	  symtype = h->type;
 	}
-- 
2.43.0


             reply	other threads:[~2023-12-05 19:06 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-12-05 19:05 Xi Ruoyao [this message]
2023-12-15 12:22 ` Ping: " Xi Ruoyao
2023-12-19  7:48   ` mengqinggang

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