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S390: Add cfi information for start routines in order to stop unwinding.

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GDB failed to detect the outermost frame while showing the backtrace
within a thread:
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

Before this patch, the start routines like thread_start had no cfi information.
GDB is then using the prologue unwinder if no cfi information is available.
This unwinder tries to unwind r15 and stops e.g. if r15 was updated or
on some jump-instructions.

On older glibc-versions (before commit "Remove cached PID/TID in clone"
c579f48edb), the thread_start function used
such a jump-instruction and GDB did not fail with an error.

This patch adds cfi information for _start, thread_start and __makecontext_ret
and marks r14 as undefined which marks the frame as outermost frame and GDB
stops the backtrace. Also tested different gcc versions in order to test
_Unwind_Backtrace() in libgcc as this is used by backtrace() in glibc.

ChangeLog:

	* sysdeps/s390/s390-64/start.S (_start): Add cfi information for r14.
	* sysdeps/s390/s390-32/start.S: (_start): Likewise
	* sysdeps/unix/sysv/linux/s390/s390-64/clone.S
	(thread_start): Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/clone.S
	(thread_start): Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S
	(__makecontext_ret): Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S
	(__makecontext_ret): Likewise.
This commit is contained in:
Stefan Liebler 2017-11-21 08:45:28 +01:00
parent 80eb52e3a9
commit 8beba15d53
7 changed files with 39 additions and 16 deletions
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13
ChangeLog
View File

@ -1,3 +1,16 @@
2017-11-21 Stefan Liebler <stli@linux.vnet.ibm.com>
* sysdeps/s390/s390-64/start.S (_start): Add cfi information for r14.
* sysdeps/s390/s390-32/start.S (_start): Likewise
* sysdeps/unix/sysv/linux/s390/s390-64/clone.S
(thread_start): Likewise.
* sysdeps/unix/sysv/linux/s390/s390-32/clone.S
(thread_start): Likewise.
* sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S
(__makecontext_ret): Likewise.
* sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S
(__makecontext_ret): Likewise.
2017-11-21 Stefan Liebler <stli@linux.vnet.ibm.com>
* include/wchar.h (__wcsnlen, __wcscat, __wcsncpy, __wcpncpy,

7
sysdeps/s390/s390-32/start.S
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@ -34,6 +34,8 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <sysdep.h>
/*
This is the canonical entry point, usually the first thing in the text
segment. Most registers' values are unspecified, except for:
@ -57,6 +59,10 @@
.globl _start
.type _start,@function
_start:
cfi_startproc
/* Mark r14 as undefined in order to stop unwinding here! */
cfi_undefined (r14)
/* Check if the kernel provides highgprs facility if needed by
the binary. */
@ -188,6 +194,7 @@ _start:
/* crash if __libc_start_main returns */
.word 0
cfi_endproc
.Llit:
#ifndef PIC
.L1: .long __libc_csu_init

7
sysdeps/s390/s390-64/start.S
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@ -34,6 +34,8 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <sysdep.h>
/*
This is the canonical entry point, usually the first thing in the text
segment. Most registers' values are unspecified, except for:
@ -57,6 +59,9 @@
.globl _start
.type _start,@function
_start:
cfi_startproc
/* Mark r14 as undefined in order to stop unwinding here! */
cfi_undefined (r14)
/* Load argc and argv from stack. */
la %r4,8(%r15) # get argv
lg %r3,0(%r15) # get argc
@ -91,6 +96,8 @@ _start:
/* Crash if __libc_start_main returns. */
.word 0
cfi_endproc
/* Define a symbol for the first piece of initialized data. */
.data
.globl __data_start

10
sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S
View File

@ -17,15 +17,9 @@
#include <sysdep.h>
/* We do not want .eh_frame info so that __makecontext_ret stops unwinding
if backtrace was called within a context created by makecontext. (There
is also no .eh_frame info for _start or thread_start.) */
#undef cfi_startproc
#define cfi_startproc
#undef cfi_endproc
#define cfi_endproc
ENTRY(__makecontext_ret)
/* Mark r14 as undefined in order to stop unwinding here! */
cfi_undefined (r14)
basr %r14,%r7
ltr %r8,%r8 /* Check whether uc_link is 0. */
jz 1f

4
sysdeps/unix/sysv/linux/s390/s390-32/clone.S
View File

@ -54,12 +54,16 @@ error:
PSEUDO_END (__clone)
thread_start:
cfi_startproc
/* Mark r14 as undefined in order to stop unwinding here! */
cfi_undefined (r14)
/* fn is in gpr 1, arg in gpr 0 */
lr %r2,%r0 /* set first parameter to void *arg */
ahi %r15,-96 /* make room on the stack for the save area */
xc 0(4,%r15),0(%r15)
basr %r14,%r1 /* jump to fn */
DO_CALL (exit, 1)
cfi_endproc
libc_hidden_def (__clone)
weak_alias (__clone, clone)

10
sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S
View File

@ -17,15 +17,9 @@
#include <sysdep.h>
/* We do not want .eh_frame info so that __makecontext_ret stops unwinding
if backtrace was called within a context created by makecontext. (There
is also no .eh_frame info for _start or thread_start.) */
#undef cfi_startproc
#define cfi_startproc
#undef cfi_endproc
#define cfi_endproc
ENTRY(__makecontext_ret)
/* Mark r14 as undefined in order to stop unwinding here! */
cfi_undefined (r14)
basr %r14,%r7
ltgr %r8,%r8 /* Check whether uc_link is 0. */
jz 1f

4
sysdeps/unix/sysv/linux/s390/s390-64/clone.S
View File

@ -55,12 +55,16 @@ error:
PSEUDO_END (__clone)
thread_start:
cfi_startproc
/* Mark r14 as undefined in order to stop unwinding here! */
cfi_undefined (r14)
/* fn is in gpr 1, arg in gpr 0 */
lgr %r2,%r0 /* set first parameter to void *arg */
aghi %r15,-160 /* make room on the stack for the save area */
xc 0(8,%r15),0(%r15)
basr %r14,%r1 /* jump to fn */
DO_CALL (exit, 1)
cfi_endproc
libc_hidden_def (__clone)
weak_alias (__clone, clone)