Date: Sun, 11 Aug 2002 05:40:58 +0900 (JST) From: NIIMI Satoshi <sa2c@sa2c.net> To: FreeBSD-gnats-submit@FreeBSD.org Subject: i386/41528: better stack alignment patch for lib/csu/i386-elf/ Message-ID: <20020810204058.33B9231D@berkeley.sa2c.net>
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>Number: 41528
>Category: i386
>Synopsis: better stack alignment patch for lib/csu/i386-elf/
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: change-request
>Submitter-Id: current-users
>Arrival-Date: Sat Aug 10 13:50:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator: NIIMI Satoshi
>Release: FreeBSD 4.6.1-RELEASE-p10 i386
>Organization:
>Environment:
System: FreeBSD berkeley.sa2c.net 4.6.1-RELEASE-p10 FreeBSD 4.6.1-RELEASE-p10 #5: Fri Aug 9 16:33:26 JST 2002 sa2c@berkeley.sa2c.net:/usr/obj/usr/src/sys/SA2C_NET i386
>Description:
Although system C compiler, GCC, maintains stack pointer to keep
aligned to 2**preferred-stack-boundary byte, C startup routine does
not care about this.
This causes a big performance penalty for floating point operations
with variables in stack frame because IA32 CPUs are optimized to
operate with aligned data.
>How-To-Repeat:
With code: foo.c
#include <stdio.h>
main()
{
double x;
printf("%p\n", &x);
}
% cc foo.c
% ./a.out
0xbfbff730 <- aligned to 8-byte boundary.
% ./a.out a
0xbfbff72c <- not aligned if command line arguments are passed.
>Fix:
(gcc 3.1 masks %esp by himself, so this patch might not be required
for -current.)
--- diff begins here ---
Index: stable/lib/csu/i386-elf/crt1.c
===================================================================
RCS file: /home/ncvs/src/lib/csu/i386-elf/crt1.c,v
retrieving revision 1.4.2.1
diff -u -r1.4.2.1 crt1.c
--- stable/lib/csu/i386-elf/crt1.c 30 Oct 2000 20:32:24 -0000 1.4.2.1
+++ stable/lib/csu/i386-elf/crt1.c 10 Aug 2002 19:40:54 -0000
@@ -93,7 +93,33 @@
monstartup(&eprol, &etext);
#endif
_init();
+#if 0
exit( main(argc, argv, env) );
+#else
+ /*
+ * GCC expects stack frame to be aligned like following figure.
+ *
+ * +--------------+
+ * |%ebp (if any) |
+ * +--------------+
+ * |return address|
+ * +--------------+ --- aligned by PREFERRED_STACK_BOUNDARY
+ * | arguments |
+ * | : |
+ * | : |
+ */
+ __asm__ ("
+ subl $12, %%esp # create stack frame for arguments
+ andl $~0xf, %%esp # align stack to 16-byte boundary
+ movl %0, 0(%%esp)
+ movl %1, 4(%%esp)
+ movl %2, 8(%%esp)
+ call main
+ movl %%eax, 0(%%esp)
+ call exit
+ hlt # do not return
+ " : : "r"(argc), "r"(argv), "r"(env));
+#endif
}
#ifdef GCRT
Index: current/lib/csu/i386-elf/crt1.c
===================================================================
RCS file: /home/ncvs/src/lib/csu/i386-elf/crt1.c,v
retrieving revision 1.9
diff -u -r1.9 crt1.c
--- current/lib/csu/i386-elf/crt1.c 16 Jul 2002 12:28:49 -0000 1.9
+++ current/lib/csu/i386-elf/crt1.c 10 Aug 2002 19:46:42 -0000
@@ -100,7 +100,33 @@
monstartup(&eprol, &etext);
#endif
_init();
+#if 0
exit( main(argc, argv, env) );
+#else
+ /*
+ * GCC expects stack frame to be aligned like following figure.
+ *
+ * +--------------+
+ * |%ebp (if any) |
+ * +--------------+
+ * |return address|
+ * +--------------+ --- aligned by PREFERRED_STACK_BOUNDARY
+ * | arguments |
+ * | : |
+ * | : |
+ */
+ __asm__ ("
+ subl $12, %%esp # create stack frame for arguments
+ andl $~0xf, %%esp # align stack to 16-byte boundary
+ movl %0, 0(%%esp)
+ movl %1, 4(%%esp)
+ movl %2, 8(%%esp)
+ call main
+ movl %%eax, 0(%%esp)
+ call exit
+ hlt # do not return
+ " : : "r"(argc), "r"(argv), "r"(env));
+#endif
}
#ifdef GCRT
--- diff ends here ---
>Release-Note:
>Audit-Trail:
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