From: Denys Vlasenko <vda.linux@googlemail.com>
Date: Sun, 17 Feb 2013 12:17:49 +0000 (+0100)
Subject: Remove wrong x32-specific lseek
X-Git-Tag: v4.8~147
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=09a87ae9712acb3725fb76d3f71215e168215611;p=strace

Remove wrong x32-specific lseek

Testing confirmed what I suspected: x32 lseek uses kernel-sized
(i.e. wide) long for offset parameter.

* file.c: Delete sys_lseek32.
* linux/syscall.h: Likewise.
* linux/x32/syscallent1.h: Likewise.
* test/x32_lseek.c: New file.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
---

diff --git a/file.c b/file.c
index 3a98674c..e5354487 100644
--- a/file.c
+++ b/file.c
@@ -528,6 +528,7 @@ static const struct xlat whence_codes[] = {
  * In kernel, off_t is always the same as (kernel's) long
  * (see include/uapi/asm-generic/posix_types.h),
  * which means that on x32 we need to use tcp->ext_arg[N] to get offset argument.
+ * Use test/x32_lseek.c to test lseek decoding.
  */
 #if defined(LINUX_MIPSN32) || defined(X32)
 int
@@ -548,27 +549,6 @@ sys_lseek(struct tcb *tcp)
 	}
 	return RVAL_LUDECIMAL;
 }
-
-# if defined(X32)
-int
-sys_lseek32(struct tcb *tcp)
-{
-	long offset;
-	int whence;
-
-	if (entering(tcp)) {
-		printfd(tcp, tcp->u_arg[0]);
-		offset = tcp->u_arg[1];
-		whence = tcp->u_arg[2];
-		if (whence == SEEK_SET)
-			tprintf(", %lu, ", offset);
-		else
-			tprintf(", %ld, ", offset);
-		printxval(whence_codes, whence, "SEEK_???");
-	}
-	return RVAL_UDECIMAL;
-}
-# endif
 #else
 int
 sys_lseek(struct tcb *tcp)
@@ -598,9 +578,9 @@ sys_lseek(struct tcb *tcp)
  *
  * hi,lo are "unsigned longs" and combined exactly this way in kernel:
  * ((loff_t) hi << 32) | lo
- * Note that for architectures with kernel's long wider than userspace longs
+ * Note that for architectures with kernel's long wider than userspace long
  * (such as x32), combining code will use *kernel's*, i.e. *wide* longs
- * for hi and lo. You may need to use tcp->ext_arg[N]!
+ * for hi and lo. We may need to use tcp->ext_arg[N]!
  */
 int
 sys_llseek(struct tcb *tcp)
diff --git a/linux/syscall.h b/linux/syscall.h
index c0f955b9..01075649 100644
--- a/linux/syscall.h
+++ b/linux/syscall.h
@@ -373,7 +373,3 @@ int sys_shmsys();
 #define SYS_shmsys_subcall	207
 #define SYS_shmsys_nsubcalls	4
 #endif
-
-#ifdef X32
-int sys_lseek32();
-#endif
diff --git a/linux/x32/syscallent1.h b/linux/x32/syscallent1.h
index 20c65292..e58372ee 100644
--- a/linux/x32/syscallent1.h
+++ b/linux/x32/syscallent1.h
@@ -4,7 +4,6 @@
 #define sys_oldstat printargs
 #define sys_oldfstat printargs
 #define sys_oldlstat printargs
-#define sys_lseek sys_lseek32
 #define sys_lstat64 sys_stat64
 #define sys_truncate64 sys_truncate
 #define sys_ftruncate64 sys_ftruncate
diff --git a/test/x32_lseek.c b/test/x32_lseek.c
new file mode 100644
index 00000000..6faa2faa
--- /dev/null
+++ b/test/x32_lseek.c
@@ -0,0 +1,38 @@
+// Test program which explores whether lseek syscall (not llseek!)
+// on x32 uses 64-bit offset argument.
+// IOW: does _kernel_ truncate it on entry?
+// The answer appears to be "no, full 64-bit offset is used".
+// strace must show it correctly too - tricky if strace itself is x32 one!
+//
+// Build: x86_64-gcc -static -Wall -ox32_lseek x32_lseek.c
+// Run:   $ strace ./x32_lseek 2>&1 | grep lseek | grep 1250999896321
+//        lseek(0, 1250999896321, SEEK_SET) = 1250999896321
+#define _GNU_SOURCE
+#include <sys/types.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/syscall.h>
+// Ensure we are compiling to 64 bits
+struct bug { int t[sizeof(long) > 4 ? 1 : -1]; };
+int main(int argc, char **argv)
+{
+	long ofs = 0x12345678901;
+	errno = 0;
+	close(0);
+	if (open("/etc/passwd", O_RDONLY))
+		return 1;
+	long r = syscall(
+		(long) (__NR_lseek | 0x40000000), // make x32 call
+		(long) (0),
+		(long) (ofs),
+		(long) (SEEK_SET)
+	);
+	printf("pos:%ld(0x%lx) errno:%m\n", r, r);
+	if (!errno)
+		printf((r == ofs) ? "64-bit offset used\n" : "Kernel truncated offset\n");
+	return 0;
+}