[glibc] i386: Avoid rely on linker optimization to avoid relocation

[glibc] i386: Avoid rely on linker optimization to avoid relocation

[Adhemerval Zanella]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=59aa41585f668b70b86a8e2617057da08f3291cc

commit 59aa41585f668b70b86a8e2617057da08f3291cc
Author: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Date:   Thu Nov 17 15:13:08 2022 -0300

    i386: Avoid rely on linker optimization to avoid relocation
    
    lld does not implement all the linker optimization to avoid the GOT
    relocation as done by binutils (bfd/elf32-i386.c:elf_i386_convert_load_reloc).
    The current 'movl main@GOT(%ebx), %eax' will then create a GOT
    relocation when building with lld, which make static-pie status to
    not being able to start the provided main function.
    
    The change uses a __wrap_main local symbol, which in turn calls main
    (similar as used by aarch64 and s390x).
    
    Checked on i686-linux-gnu with binutils and lld.
    Reviewed-by: Fangrui Song <maskray@google.com>

Diff:
---
 sysdeps/i386/start.S | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/sysdeps/i386/start.S b/sysdeps/i386/start.S
index 4ec04bdfd7..23e4f2b012 100644
--- a/sysdeps/i386/start.S
+++ b/sysdeps/i386/start.S
@@ -98,11 +98,10 @@ ENTRY (_start)
 	pushl main@GOT(%ebx)
 # else
 	/* Avoid relocation in static PIE since _start is called before
-	   it is relocated.  Don't use "leal main@GOTOFF(%ebx), %eax"
-	   since main may be in a shared object.  Linker will convert
-	   "movl main@GOT(%ebx), %eax" to "leal main@GOTOFF(%ebx), %eax"
+	   it is relocated.  This also avoid rely on linker optimization to
+	   transform 'movl main@GOT(%ebx), %eax' to 'leal main@GOTOFF(%ebx)'
 	   if main is defined locally.  */
-	movl main@GOT(%ebx), %eax
+	leal __wrap_main@GOTOFF(%ebx), %eax
 	pushl %eax
 # endif
 
@@ -130,6 +129,12 @@ ENTRY (_start)
 1:	movl	(%esp), %ebx
 	ret
 #endif
+
+#if defined PIC && !defined SHARED
+__wrap_main:
+	_CET_ENDBR
+	jmp	main@PLT
+#endif
 END (_start)
 
 /* To fulfill the System V/i386 ABI we need this symbol.  Yuck, it's so