[Bug c/17455] New: syscall_linkage attribute problem with sibling call optimization

[Bug c/17455] New: syscall_linkage attribute problem with sibling call optimization

[eranian at hpl dot hp dot com]

We have found aproblem in the Linux/ia64 kernel related to sibling call
optimization and the syscall_linkage attribute. On this platform, the attribute
indicates that the function paramaters must be treated as read-only
by the compiler. Any modification requires making a copy. 

The following code give an example of the problem we are describing:

void
bar(void)
{
        printf("in syscall_trace\n");
}

void foo(long value) __attribute__((syscall_linkage));
void
foo (long value)
{
        bar();
}

Because foo() is so simple, and bar() is the last call, the compiler
generates a direct branch to bar as opposed to a normal function call.
The bar() function will return directly to the caller of foo().

The generated code at -O2 looks as follows:

0000000000000000 <bar>:
   0:   [MII]       alloc r33=ar.pfs,4,3,0
   6:               mov r32=b0
   c:               addl r35=0,r1
  10:   [MMI]       mov r34=r1;;
  16:               ld8 r35=[r35]
  1c:               nop.i 0x0
  20:   [MIB]       nop.m 0x0
  26:               nop.i 0x0
  2c:               br.call.sptk.many b0=20 <bar+0x20>;;
  30:   [MII]       mov r1=r34
  36:               mov.i ar.pfs=r33
  3c:               mov b0=r32
  40:   [MIB]       nop.m 0x0
  46:               nop.i 0x0
  4c:               br.ret.sptk.many b0;;

0000000000000050 <foo>:
  50:   [MMI]       alloc r16=ar.pfs,8,8,0;;
  56:               alloc r2=ar.pfs,8,0,0
  5c:               nop.i 0x0
  60:   [MIB]       nop.m 0x0
  66:               nop.i 0x0
  6c:               br.many 60 <foo+0x10>;;
  70:   [MFB]       nop.m 0x0
  76:               break.f 0x0
  7c:               nop.b 0x0;;

foo() cannot modify r32 (the first argument) because of the syscall_linkage
attibute. However bar() is allowed to. 

The sibling optimization makes a direct branch (br.many) to bar().
That branch does not actually "protect" r32 because no RSE movement occurs.
The alloc in bar() simply resizes its current frame but the same r32 that
was passed to foo() is also accessible and can be modified at will.

In functions with the syscall_linkage attribute, sibling call optimization
should not be done because it could break the guarantee offered by the
attribute.

-- 
           Summary: syscall_linkage attribute  problem with sibling call
                    optimization
           Product: gcc
           Version: 3.3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: eranian at hpl dot hp dot com
                CC: gcc-bugs at gcc dot gnu dot org,wilson at specifixinc
                    dot com
 GCC build triplet: ia64-linux
  GCC host triplet: ia64-linux
GCC target triplet: ia64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17455

[Bug target/17455] syscall_linkage attribute problem with sibling call optimization

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c                           |target


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17455

[Bug target/17455] syscall_linkage attribute problem with sibling call optimization

[wilson at gcc dot gnu dot org]

------- Additional Comments From wilson at gcc dot gnu dot org  2004-09-13 20:01 -------
Created an attachment (id=7124)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=7124&action=view)
Disable sibcalls from syscall_linkage functions.

This fixes the bug for me.  I will do the usual testing, and then check it in. 
Since this is a kernel miscompilation problem, I will add the patch to mainline
and gcc-3.4, and also try to get it into gcc-3.3.  The testing will take a few
days.  I will try building a kernel to see what happens, but I won't try
booting it.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17455

[Bug target/17455] syscall_linkage attribute problem with sibling call optimization

[wilson at gcc dot gnu dot org]

------- Additional Comments From wilson at gcc dot gnu dot org  2004-09-13 20:02 -------
Mine.  IA-64.  Problem confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |wilson at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2004-09-13 20:02:42
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17455

[Bug target/17455] syscall_linkage attribute problem with sibling call optimization

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2004-09-15 23:26 -------
Subject: Bug 17455

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	wilson@gcc.gnu.org	2004-09-15 23:26:37

Modified files:
	gcc            : ChangeLog 
	gcc/config/ia64: ia64.c 

Log message:
	Fix linux kernel miscompilation.
	PR target/17455
	* config/ia64/ia64.c (ia64_function_ok_for_sibcall): Return false
	if current_function_decl is a sibcall.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.5471&r2=2.5472
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/config/ia64/ia64.c.diff?cvsroot=gcc&r1=1.323&r2=1.324



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17455

[Bug target/17455] syscall_linkage attribute problem with sibling call optimization

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2004-09-17 17:56 -------
Subject: Bug 17455

CVSROOT:	/cvs/gcc
Module name:	gcc
Branch: 	gcc-3_3-branch
Changes by:	wilson@gcc.gnu.org	2004-09-17 17:56:35

Modified files:
	gcc            : ChangeLog 
	gcc/config/ia64: ia64.c 

Log message:
	Fix linux kernel miscompile.
	PR target/17455
	* config/ia64/ia64.c (ia64_function_ok_for_sibcall): Return false
	if current_function_decl is a sibcall.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-3_3-branch&r1=1.16114.2.1016&r2=1.16114.2.1017
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/config/ia64/ia64.c.diff?cvsroot=gcc&only_with_tag=gcc-3_3-branch&r1=1.198.2.21&r2=1.198.2.22



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17455

[Bug target/17455] [3.4 only] syscall_linkage attribute problem with sibling call optimization

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
      Known to fail|                            |3.4.0 3.3.3
      Known to work|                            |3.3.5 4.0.0
            Summary|syscall_linkage attribute   |[3.4 only] syscall_linkage
                   |problem with sibling call   |attribute  problem with
                   |optimization                |sibling call optimization
   Target Milestone|---                         |3.4.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17455

[Bug target/17455] [3.4 only] syscall_linkage attribute problem with sibling call optimization

[mmitchel at gcc dot gnu dot org]

------- Additional Comments From mmitchel at gcc dot gnu dot org  2004-11-01 00:46 -------
Postponed until GCC 3.4.4.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.4.3                       |3.4.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17455

[Bug target/17455] [3.4 only] syscall_linkage attribute problem with sibling call optimization

[wilson at gcc dot gnu dot org]

------- Additional Comments From wilson at gcc dot gnu dot org  2005-04-23 01:15 -------
The patch is actually on the gcc-3.4 branch already, I added it Sept 15, 2004. 
I must have forgotten to include the PR line in the cvs log entry, ergo no CVS
commit message in the PR.  And I also forgot to close it.

Fixed on gcc-3.3, gcc-3.4, and mainline (pre gcc-4 branch).


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|3.3.5 4.0.0                 |3.3.5 4.0.0 3.4.3
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17455