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Optimize sys_old_mmap

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* mem.c (sys_old_mmap): For Ia64 and 32-bit personality of x86-64,
copy narrow parameters from userspace by single umove, not by six
separate ones; then assign them to long u_arg[i]. For SH[64],
avoid copying of tcp->u_arg.
(sys_mmap): Add FIXME comment - SH64 and i386 seem to be handled
differently for no apparent reason.
* test/mmap_offset_decode.c: New test program, illustrates FIXME.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
This commit is contained in:
Denys Vlasenko 2011-08-19 17:07:38 +02:00
parent 31f9cb6f48
commit 9aa97968ed
2 changed files with 59 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

53
mem.c
View File

@ -265,46 +265,44 @@ print_mmap(struct tcb *tcp, long *u_arg, long long offset)
#ifdef LINUX
int sys_old_mmap(struct tcb *tcp)
{
long u_arg[6];
#if defined(IA64)
int i, v;
/*
* IA64 processes never call this routine, they only use the
* new `sys_mmap' interface. This code converts the integer
* arguments that the IA32 process pushed onto the stack into
* longs.
* IA64 processes never call this routine, they only use the
* new `sys_mmap' interface.
* For IA32 processes, this code converts the integer arguments
* that they pushed onto the stack, into longs.
*
* Note that addresses with bit 31 set will be sign extended.
* Fortunately, those addresses are not currently being generated
* for IA32 processes so it's not a problem.
* Note that addresses with bit 31 set will be sign extended.
* Fortunately, those addresses are not currently being generated
* for IA32 processes so it's not a problem.
*/
int i;
long u_arg[6];
int narrow_arg[6];
if (umoven(tcp, tcp->u_arg[0], sizeof(narrow_arg), (char *) narrow_arg) == -1)
return 0;
for (i = 0; i < 6; i++)
if (umove(tcp, tcp->u_arg[0] + (i * sizeof(int)), &v) == -1)
return 0;
else
u_arg[i] = v;
u_arg[i] = narrow_arg[i];
#elif defined(SH) || defined(SH64)
/* SH has always passed the args in registers */
int i;
for (i = 0; i < 6; i++)
u_arg[i] = tcp->u_arg[i];
long *u_arg = tcp->u_arg;
#else
long u_arg[6];
# if defined(X86_64)
if (current_personality == 1) {
int i;
for (i = 0; i < 6; ++i) {
unsigned int val;
if (umove(tcp, tcp->u_arg[0] + i * 4, &val) == -1)
return 0;
u_arg[i] = val;
}
unsigned narrow_arg[6];
if (umoven(tcp, tcp->u_arg[0], sizeof(narrow_arg), (char *) narrow_arg) == -1)
return 0;
for (i = 0; i < 6; ++i)
u_arg[i] = narrow_arg[i];
}
else
# endif
if (umoven(tcp, tcp->u_arg[0], sizeof u_arg, (char *) u_arg) == -1)
if (umoven(tcp, tcp->u_arg[0], sizeof(u_arg), (char *) u_arg) == -1)
return 0;
#endif /* !IA64 && !SH[64] */
#endif /* other architectures */
return print_mmap(tcp, u_arg, u_arg[5]);
}
#endif /* LINUX */
@ -314,6 +312,11 @@ sys_mmap(struct tcb *tcp)
{
long long offset = tcp->u_arg[5];
/* FIXME: why only SH64? i386 mmap2 syscall ends up
* in this function, but does not convert offset
* from pages to bytes. See test/mmap_offset_decode.c
* Why SH64 and i386 are handled differently?
*/
#if defined(LINUX) && defined(SH64)
/*
* Old mmap differs from new mmap in specifying the

31
test/mmap_offset_decode.c Normal file
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@ -0,0 +1,31 @@
/* Should strace show byte or page offsets in mmap syscalls
* which take page offset parameters?
*
* At the time of writing, sys_mmap() converts page to byte offsets,
* but only for SH64! But this routine is used on i386 too - by mmap2 syscall,
* which uses page offsets too. As it stands now, SH64 and i386 are inconsistent.
*
* sys_old_mmap() is used for old mmap syscall, which uses byte offset -
* should be ok.
* sys_mmap64() is currently buggy (should print bogus offset, but I can't
* test it right now. What arch/bitness invokes sys_mmap64?)
*
* This program is intended for testing what strace actually shows. Usage:
* $ gcc test/mmap_offset_decode.c -o mmap_offset_decode -static
* $ strace ./mmap_offset_decode
*
* As of today (2011-08), on i386 strace prints page offset.
*/
#define _LARGEFILE_SOURCE
#define _LARGEFILE64_SOURCE
#define _FILE_OFFSET_BITS 64
#include <sys/mman.h>
#include <errno.h>
int main()
{
/* 0x1000 is meant to be page size multiplier */
mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0x7fff0000LL * 0x1000);
return errno != 0;
}