From: Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>
To: libc-alpha@sourceware.org, Fangrui Song <maskray@google.com>,
"H . J . Lu" <hjl.tools@gmail.com>
Subject: [PATCH] i386: Avoid avoid rely on linker optimization to avoid relocation
Date: Thu, 17 Nov 2022 09:43:17 -0300 [thread overview]
Message-ID: <20221117124317.2816607-1-adhemerval.zanella@linaro.org> (raw)
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.
---
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..d593c4de00 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
+#endif
END (_start)
/* To fulfill the System V/i386 ABI we need this symbol. Yuck, it's so
--
2.34.1
next reply other threads:[~2022-11-17 12:43 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-17 12:43 Adhemerval Zanella via Libc-alpha [this message]
2022-11-17 16:07 ` [PATCH] i386: Avoid avoid rely on linker optimization to avoid relocation H.J. Lu via Libc-alpha
2022-11-17 16:41 ` Adhemerval Zanella Netto via Libc-alpha
2022-11-17 16:52 ` H.J. Lu via Libc-alpha
2022-11-17 17:28 ` Adhemerval Zanella Netto via Libc-alpha
2022-11-17 18:01 ` H.J. Lu via Libc-alpha
2022-11-21 14:47 ` Andreas Schwab via Libc-alpha
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