Patchwork [committed] aarch64: fix static pie enabled libc when main is in a shared library

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Submitter Szabolcs Nagy
Date Jan. 12, 2018, 6:13 p.m.
Message ID <5A58FAE2.4050905@arm.com>
Download mbox | patch
Permalink /patch/25366/
State New
Headers show

Comments

Szabolcs Nagy - Jan. 12, 2018, 6:13 p.m.
In the static pie enabled libc, crt1.o uses the same position independent
code as rcrt1.o, and crt1.o is used instead of Scrt1.o when -no-pie
executables are linked.  When main is not defined in the executable, but
in a shared library crt1.o is currently broken, it assumes main is local.
(glibc has a test for this but i missed it in my previous testing.)

To make both rcrt1.o and crt1.o happy with the same code, a wrapper is
introduced around main: with this crt1.o works with extern main symbol
while rcrt1.o does not depend on GOT relocations. (The change only
affects static pie enabled libc. Further simplification of start.S is
possible in the future by using the same approach for Scrt1.o too.)

2018-01-12  Szabolcs Nagy  <szabolcs.nagy@arm.com>

	* aarch64/start.S (_start): Use __wrap_main.
	(__wrap_main): New local symbol.

Patch

diff --git a/ChangeLog b/ChangeLog
index 971257a4bd..da74352ce1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@ 
+2018-01-12  Szabolcs Nagy  <szabolcs.nagy@arm.com>
+
+	* aarch64/start.S (_start): Use __wrap_main.
+	(__wrap_main): New local symbol.
+
 2018-01-12  Dmitry V. Levin  <ldv@altlinux.org>
 
 	[BZ #22679]
diff --git a/sysdeps/aarch64/start.S b/sysdeps/aarch64/start.S
index 9f3b4188db..bad000f555 100644
--- a/sysdeps/aarch64/start.S
+++ b/sysdeps/aarch64/start.S
@@ -71,8 +71,8 @@  _start:
         adrp    x4, :got:__libc_csu_fini
 	ldr     PTR_REG (4), [x4, #:got_lo12:__libc_csu_fini]
 # else
-	adrp	x0, main
-	add	x0, x0, :lo12:main
+	adrp	x0, __wrap_main
+	add	x0, x0, :lo12:__wrap_main
 	adrp	x3, __libc_csu_init
 	add	x3, x3, :lo12:__libc_csu_init
 	adrp	x4, __libc_csu_fini
@@ -94,6 +94,15 @@  _start:
 	/* should never get here....*/
 	bl	abort
 
+#if defined PIC && !defined SHARED
+	/* When main is not defined in the executable but in a shared library
+	   then a wrapper is needed in crt1.o of the static-pie enabled libc,
+	   because crt1.o and rcrt1.o share code and the later must avoid the
+	   use of GOT relocations before __libc_start_main is called.  */
+__wrap_main:
+	b	main
+#endif
+
 	/* Define a symbol for the first piece of initialized data.  */
 	.data
 	.globl __data_start