[Qemu-devel] [PATCH] getpriority() shouldn't use libc wrapper

[Qemu-devel] [PATCH] getpriority() shouldn't use libc wrapper

[Thayne Harbaugh]

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The linux-user getpriority() syscall goes through the libc wrapper.
This causes a problem because the libc wrapper remaps the return value
from the kernel.  This patch calls the kernel getpriority syscall
directly.


[-- Attachment #2: 47_getpriority.patch --]
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Index: qemu/linux-user/syscall.c
===================================================================
--- qemu.orig/linux-user/syscall.c	2007-09-26 13:13:40.000000000 -0600
+++ qemu/linux-user/syscall.c	2007-09-26 14:10:29.000000000 -0600
@@ -174,6 +174,7 @@
 #define __NR_sys_getcwd1 __NR_getcwd
 #define __NR_sys_getdents __NR_getdents
 #define __NR_sys_getdents64 __NR_getdents64
+#define __NR_sys_getpriority __NR_getpriority
 #define __NR_sys_linkat __NR_linkat
 #define __NR_sys_mkdirat __NR_mkdirat
 #define __NR_sys_mknodat __NR_mknodat
@@ -229,6 +230,7 @@
 #if defined(TARGET_NR_getdents64) && defined(__NR_getdents64)
 _syscall3(int, sys_getdents64, uint, fd, struct dirent64 *, dirp, uint, count);
 #endif
+_syscall2(int, sys_getpriority, int, which, int, who);
 _syscall5(int, _llseek,  uint,  fd, ulong, hi, ulong, lo,
           loff_t *, res, uint, wh);
 #if defined(TARGET_NR_linkat) && defined(__NR_linkat)
@@ -4010,7 +4012,10 @@
         break;
 #endif
     case TARGET_NR_getpriority:
-        ret = get_errno(getpriority(arg1, arg2));
+        /* libc does special remapping of the return value of
+         * sys_getpriority() so it's just easiest to call
+         * sys_getpriority() directly rather than through libc. */
+        ret = sys_getpriority(arg1, arg2);
         break;
     case TARGET_NR_setpriority:
         ret = get_errno(setpriority(arg1, arg2, arg3));

Re: [Qemu-devel] [PATCH] getpriority() shouldn't use libc wrapper

[Thayne Harbaugh]

On Wed, 2007-09-26 at 14:06 -0600, Thayne Harbaugh wrote:
> The linux-user getpriority() syscall goes through the libc wrapper.
> This causes a problem because the libc wrapper remaps the return value
> from the kernel.  This patch calls the kernel getpriority syscall
> directly.

I didn't see any discussion about this nor did I see it committed.  Were
there any concerns or objections?  It fixes several failures in the LTP
test suite.

The bug is that the kernel returns -1 on error and 1-40 on success - the
libc wrapper remaps this to -1 or error and -20 - 19 on succes (errno
must be cleared and checked for the -1 case to determine if there was an
error).  If qemu uses the libc wrapper then the return value is aleady
remapped to negative numbers - which appear to be errors.