Optimize sys_old_mmap
* 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>
diff --git a/mem.c b/mem.c
index de9b6bb..7ae8b5c 100644
--- a/mem.c
+++ b/mem.c
@@ -265,46 +265,44 @@
#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 @@
{
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
diff --git a/test/mmap_offset_decode.c b/test/mmap_offset_decode.c
new file mode 100644
index 0000000..875ea9c
--- /dev/null
+++ b/test/mmap_offset_decode.c
@@ -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;
+}